Batteries that are capable of being oper_Practical Hand Book of Gas, Oil and Steam Engines Stationary, Marine, Traction; Gas Burners, Oil Burners, Etc.; Farm, Traction, Automobile, Locomotive; A simple, practical and comprehensive book on the construction, operation and repair of all kinds of engines. Dealing with the various parts in detail and the various types of engines and also the use of different kinds of fuel.

account of polarization, are called open circuit batteries. Open circuit

batteries are cheaper and more simple than closed circuit batteries. For

ignition purposes, a battery is made that is a compromise between the

closed and open circuit cells, this being a battery in which the

polarization is only partially suppressed. As the demand for current on

an ignition battery is small with comparatively long rests between

contacts, the compromise battery answers the purpose and is fairly

cheap.

All primary batteries are in reality wet batteries, for the reason that

it would be impossible to cause a chemical reaction and a current with a

dry electrolyte. The action of dry and wet batteries is identical.

There are many types of wet battery in use for various purposes, but few

of them are adapted for gas engine ignition because of a tendency to

polarize or because of the cost of maintenance.

All wet batteries are not suitable for portable or automobile engines

because of the slopping of the liquid electrolyte and the danger of

breaking the containing jars. Their weight and bulk is also a drawback.

If the electrolyte or the electrodes be made of impure material local

currents will be generated. These currents decrease the life of the cell

without producing any useful current in the ignition circuit. Due to the

deteriorating effects of the local currents, batteries standing idle for

several months will often be found to be completely discharged and

worthless without having done any useful work. In the better grade of

cells this loss is reduced to a minimum.

A type of wet battery using a solution of caustic soda for an

electrolyte, and having zinc and copper oxide electrodes, is extensively

used for stationary ignition purposes, and is the most satisfactory type

of wet cell for continuous work with this class of engine. The caustic

soda battery is of the =CLOSED= circuit type, and is capable of

furnishing a strong uniform current without danger of polarization.

The hydrogen bubbles which cause polarization are oxidized or eliminated

by the copper oxide electrode as soon as they are formed. The hydrogen

combines with the oxygen of the copper oxide forming water.

The copper oxide is gradually reduced to metallic copper by the reaction

with the hydrogen, and in the course of time requires renewal. The

copper oxide element is rather expensive and cannot be obtained as

readily as the electrodes used in other cells.

It will be noted that both electrodes are consumed in the caustic

battery, the consumption of the zinc furnishing the current, and the

reducing of the oxide furnishing the chemical energy for depolarizing

the cell.

(81) Dry Batteries.

Dry batteries are by far, the most convenient and economical form of

primary battery to use, for there is no fluid to slop and leak, the

first cost is low, the output is large for the weight, and last but not

least, the cell can be thrown away when exhausted without great monetary

loss. This does away with the expense and annoyance of changing wet

cells, a factor that will be appreciated by those that are far from a

source of chemical supplies. Since the advent of the automobile the use

of dry cells has extended so that they may be obtained in almost any

country town or village.

While the cell is not dry, strictly speaking, the solution is held in

such a way that it cannot slop around in the cell nor leak out of the

seal. The only fault of a dry cell is its tendency to deteriorate with

age because of the constant contact of the electrolyte with the

electrodes.

The negative electrode of the dry cell (zinc) is in the form of a cup

which serves as a containing vessel for the electrolyte and the

depolarizer.

The electrolyte is usually composed of a solution of ammonium chloride,

with a small percentage of zinc sulphate, this fluid being held by some

absorbent material such as blotting paper, or paper pulp.

The electrolyte is applied to the electrodes by means of the saturated

blotting paper, which is also used to line the zinc container, thus

providing insulation between the electrodes.

A rod of solid carbon which forms the positive electrode is placed in

the center of the container, and the space between the rod and the zinc

is packed solidly with granulated carbon, the blotting paper lining

preventing contact of the zinc with the carbon.

Pulverized manganese dioxide is mixed with the granulated carbon for a

depolarizer.

[Illustration:

Brookes Four Cylinder Gasoline Engine Direct Connected to Dynamo.

]

After the zinc container is filled with the electrolyte and pulverized

carbon, the top of the container is closed hermetically by means of

sealing wax. Granulated carbon is used for it presents a large surface

to the electrolyte, reduces the internal resistance of the cell, and

therefore increases the current output of the battery.

As soon as the battery starts generating current, polarization begins,

with the liberation of hydrogen gas. If the cell is discharged at a high

rate, the manganese dioxide will be unable to absorb all of the gas, and

consequently pressure will be erected within the cell. The greater the

rate of discharge, the greater will be the amount of hydrogen set free,

and the higher the pressure.

If a short circuit exists for any length of time, the pressure of the

excess hydrogen will speedily ruin it, as the cell will puff up, or even

burst under the pressure. If the rate of discharge be kept so low that

all of the gas will be absorbed by the manganese, as soon as generated,

the cell will furnish a steady current until the elements of the cell or

the electrolyte are exhausted.

The steady current limit, or non-polarizing limit is about one-half

ampere and if long life of the cell is expected, the current drain

should be less than this amount. A good spark coil will develop a

satisfactory spark on a quarter to one-half ampere, so that the demand

of a good coil is well within the safe limits of battery capacity. The

voltage of the average dry cell when in good condition is 1.5 volts on

open circuit. When the cell is old or exhausted, the voltage falls

rapidly when any demand for current is made on the cell, and the voltage

also varies with the rate of current flow, the voltage decreasing with

an increase of current.

As there is not much difference in voltage between a new and old cell

when on open circuit, it will be seen that the ammeter giving the

current output will give a more accurate determination of the condition

of the battery. The voltage is independent of the size of cell.

The battery showing the greatest amperage is not necessarily the best

for general use, as cells having an unusually high current capacity are

generally short lived. The strong electrolyte used in high ampere

batteries causes them to burn out or deteriorate rapidly when not in

use.

Under ordinary conditions, a correctly proportioned No. 6 ignition cell

should show a current of from fifteen to twenty amperes on short circuit

when the cell is new, although higher results may be obtained safely

with some makes of cells.

While the voltage is the same for all sizes of batteries, and depends on

the material used in the construction, the amperes increase with the

size of the cell, and the area of the electrodes.

If a cell does not show more than ten amperes on short circuit, it

should be thrown out and another substituted for it, as the cell is

liable to go out of commission at any minute when reaching this point of

exhaustion.

A small battery testing voltmeter or ammeter should be in the kit of

every gas engine operator using a battery for ignition, as the exact

condition of a vital part of the power plant can be determined quickly

and with accuracy. For dry batteries an ammeter is preferable; for

storage batteries a voltmeter must be used.

When buying dry batteries insist on having new, fresh cells, as any

battery depreciates in value with age. Never take a cell without testing

it, as it is the practice of dealers to work off their old stock on

unsuspecting customers. Examine the battery closely for the makers’

dates, and if the battery is several months old, it is probable that the

electrolyte is dried up or that the electrodes are wasted through long

continued local action. As heat stimulates chemical action in the cell,

they should be stored in a cool place to retard the wasting action as

much as possible. Under all conditions, the cell should be kept dry,

since the moisture that is deposited on the cell forms a closed circuit

for the current which soon exhausts the battery. Cold retards chemical

action in the cell and consequently reduces the output in zero weather

to such an extent that starting is frequently impossible.

Multiple cylinder engines exhaust a battery quicker than those with a

single cylinder, as there are more current impulses in a given time and

consequently more current is used. A battery may be compared with a

bottle that holds a certain quantity of fluid. If the water is allowed

to drip out slowly it will last for a long time, but if allowed to flow

in a continuous stream will soon be exhausted.

With badly designed or poorly adjusted spark coil, the demand on the

batteries is greater than with one that is in proper condition. An

engine that runs continuously exhausts a battery faster than one that is

run at long intervals. Always open the battery switch when the engine is

to be idle for any length of time, as the engine may have stopped with

the igniter in contact, allowing the battery to expend its energy

uselessly.

Test batteries immediately after a run, as the batteries will recover

after standing a while, and will show a fictitious value.

A weak, partially exhausted battery will cause a poor spark that will

result in misfiring or a loss of power. It is poor economy to attempt

running an engine on a weak battery. An engine may run on a weak battery

for a short time, and then gradually decrease in speed until it comes to

a full stop. Misfiring is generally in evidence as the engine dies down.

In case of an emergency, weak batteries may be made to run an engine of

an automobile or boat to its destination, by stopping the engine

frequently and allowing the batteries to recuperate during the idle

periods. A battery that is temporarily weakened by hard service or by a

temporary short circuit will usually revive or partially recover its

strength if allowed to “rest” for a short time until the hydrogen is

absorbed by the depolarizing material. The life of a dry cell can be

extended for a few hours by punching a hole in the sealing wax on the

top of the battery, and pouring water, or a solution of water and

sal-ammoniac into the cell. This will reduce the internal resistance and

increase the current. The batteries will run under these conditions for

a short time only, and new cells should be procured at the earliest

possible moment. No old cell can be made as good as new by any method.

Never drop the cells on the floor nor subject them to hard usage

mechanically, for if the active material is loosened, the current output

will be reduced. A short circuit through a closed switch with the engine

stopped or a loose dangling wire will put the cells beyond repair.

If the binding screw on the carbon electrode does not make good contact

with the carbon, tighten it to decrease the resistance. Fasten the

connecting wires firmly under the binding screws and keep the

connections clean.

In the absence of an ammeter, a rough estimate of the condition of the

cell may be made by fastening a short wire tightly in the zinc binding

post, and touching the carbon surface lightly and intermittently with

the free end of the wire. When contact is made with the free end of the

wire, a small puff of smoke will arise and a red spark will be seen if

the cell is in good condition.

Sometimes the contact made on the carbon will produce only a small black

ring on the surface of the electrode. This indicates a battery that is

nearly exhausted, and one which is good for only a few more hours of

service.

When a number of cells are connected together in such a way that they

collectively form a single source of current, the group is called a

battery, and the resulting voltage and amperes of the group depends on

the way in which the cells are interconnected.

It is possible to connect the cells of a battery in such a way that

total voltage of the group or battery is equal to the sum of the

voltages of the individual cells. A battery connected in this manner is

said to be connected in series. While the voltage of a battery is

increased, by series connection, the number of amperes is the same as

that given by a single cell, the same current flowing through the set.

(82) Series and Multiple Connections.

Fig. 86 shows the cells connected in series, the carbon terminal of one

cell being connected to the zinc terminal of the second. The carbon of

the second cell is connected to the zinc of the third, and so on

throughout the series, the two remaining terminals of the battery being

connected with the ignition circuit. The number of watts or power

developed by the group is equal to the sum of the outputs of the

separate cells. If the voltage of each cell shown in diagram is 1.5

volts, the total voltage of the group of five cells will be 1.5 × 5 =

7.5 volts, and if the current of a single cell is 15 amperes, the

current output of the group will be 15 amperes, or the same as that of a

single cell. Almost all ignition apparatus now on the market requires

six volts for its operation, so with cells having a voltage of 1.5 volts

such apparatus would call for four cells in series, as 6 ÷ 1.5 = 4.

[Illustration:

Fig. 86. Five Cells in Series.

]

Owing to the increase of internal resistance caused by series

connections it is usual to add one more cell than is theoretically

required, making a group of five cells to supply the six volts required.

A large number of cells will give a hotter spark than a smaller, but the

excessive current causes the contact points of the igniter or vibrator

to burn off rapidly and also hastens the destruction of the cells

themselves.

Batteries connected in such a way that the total amperes of the group is

increased without increased voltage are said to be connected in multiple

or parallel. When batteries are connected in multiple, the total current

in amperes is equal to the sum of the amperes delivered by the separate

cells; and, while the current in amperes is increased by multiple

connection, the voltage of the group remains equal to that of a single

cell.

If each cell connected in multiple has an electromotive force of 1.5

volts, and can deliver 15 amperes, the total current delivered by this

system of connection will be 15 × 5 = 75 amperes with five cells, and

the electromotive force will be 1.5 volts as in the case of the single

cell. By connecting batteries in multiple, the resistance is reduced,

allowing a maximum flow of current. The demand on the individual cells

is reduced by multiple connection, as each cell only furnishes a small

part of the total current. The greater the number of cells, the less

will be the current required per cell, with a given total current. As

the life of a battery depends entirely upon the rate at which it is

discharged, it is necessary, for economical reasons, to keep the current

per cell as small as possible, therefore the multiple system would prove

of value as it reduces the load to the smallest possible limit. Enough

cells should be placed in multiple to reduce the current to less than a

quarter of an ampere per cell. The cells shown will not have sufficient

voltage to operate ordinary ignition apparatus requiring a potential of

six volts, hence the multiple system must be modified in order to have

an increased voltage, and at the same time secure the advantages of

multiple connections.

(83) Multiple-Series Connections.

A compromise is affected by the multiple series system of connections in

which are combined the advantages of both the series and multiple

systems of connection.

This arrangement allows sufficient voltage to operate 6 volt apparatus

and at the same time reduces the rate of discharge on the individual

cells. The series-multiple battery shown in the diagram 88 consists of

four groups of batteries connected in multiple, each group of which

consists of five cells that are connected in series. The current and

voltage in the various branches is shown in the diagram. The

series-multiple system is adapted for use with multiple cylinder

engines, as engines with more than one cylinder cause a severe drain on

the ignition system. Arranging the series groups in parallel increases

the life and efficiency of the cells. If an efficient coil is used, the

drain of a single cylinder is not too great to be met with a single set

of series cells. If possible the set should be provided with a

duplicate, so that the load could be transferred from one set to the

other at proper intervals by means of a double throw switch.

With a single set of batteries in series the working life of the cells

will be approximately twenty hours under ordinary conditions. With four

groups of four cells in series, the life of the cell will be

approximately 160 hours, or eight times the life of the single set under

similar conditions.

While the cost of the cells will be only four times that of the single

set, it will be seen that the cost of battery upkeep is halved by

reducing the demand on the cells.

Sometimes duplicate sets of series multiple connected batteries are used

for heavy duty engines, the engine running on one set for a while and

then on the other, allowing the first set to thoroughly recuperate

before it is again thrown in service, by means of the double throw

switch.

When batteries are multiple or series-multiple connected they should be

of the same size and make and of the same voltage. If the cells are of

different voltages useless local currents will circulate among the

cross-connections, shortening the life of the battery and reducing the

output.

[Illustration:

Fig. 88. Cells in Multiple Series.

]

In connecting a dry cell use a good grade of rubber insulated wire,

preferably wire with a stranded conductor, as it is less liable to break

or loosen at the binding screw of the battery. Carefully remove the

insulation from the end of the wire that is to be fastened under the

binding screw of the battery. Scrape it until it is bright and perfectly

free from dirt before fastening it in the battery terminal. Never allow

a dirty or corroded connection or a loose wire to exist. An open battery

circuit or loose connection will stop engine suddenly, or will prevent

starting.

The battery connections should be screwed down tight with the pliers,

care being taken that the screws are not broken by the tightening

process. See that frayed ends of the wire do not project beyond the

binding screw to which they are connected and make contact with other

cells or metal objects. Be sure that no insulation gets between the

contact braces of the binding screw.

(84) Operation of Dry Cells.

The following hints should be observed to obtain the best results with

dry cells.

(1) Never remove the paper jackets from the cells.

(2) Never lay tools or other metallic objects on top of the cells for

this will cause a “short” that will quickly exhaust them.

(3) Do not connect old and new cells together, especially with the

multiple-series system of connections, for the old cells will limit the

output of the new, or else will cause cross-currents that will exhaust

all of them.

(4) When trouble develops in the battery, test each cell separately and

remove the faulty cells. Do not reject all of the battery because of one

or two dead cells.

(5) Place the cells in a wooden box that will protect them from dirt or

moisture, and if possible divide the box off into pigeon holes with a

cell in each hole. For the best protection against moisture, the box

should be boiled in paraffine.

(6) Provide a battery switch on the box that will cut both leads from

the cells completely out of circuit when the engine is stopped.

(7) Never place a dry cell in a box that has contained storage cells

unless the box has been thoroughly washed out, for the residual acid of

the battery will destroy the zinc elements.

(8) Make all connections firmly with well insulated wire and take care

that the wire does not make contact with any part of the battery except

that to which it is connected.

(9) Keep the battery dry.

(85) Storage Batteries.

The purpose of the storage battery is to store or accumulate the current

generated by a dynamo until so that the current will be available when

the dynamo is not running. A storage cell does not “store” current in

the same way that water is held in a tank, but returns the energy

expended on it through the chemical changes caused in the cell by the

current.

When the charging current passes through the storage battery chemical

changes are produced in the electrodes and electrolyte, and the energy

expended on the cell is in the form of latent chemical energy, in which

state it remains until the electrodes are connected with one another by

a wire or some other conducting medium. When the electrodes are

connected through an external circuit, the electrolyte acts on the

electrodes causing them to assume their original composition. As they

pass into their previous chemical condition the latent chemical energy

is converted into electrical energy. The current thus produced may be

used in the same way as in a primary cell.

When discharging, the action of a storage battery is similar to that of

a primary battery, the current being produced by the action of a fluid

on two dissimilar electrodes. Instead of supplying new elements when the

battery is discharged, as in the case of the primary cell, the elements

are brought back to their original state by passing a current through

the cell in the opposite direction to that of the discharge.

There are several combinations of materials which may be used in the

making of storage battery electrodes and electrolytes, but with the

exception of the lead sulphuric battery and the new Edison battery none

have proven a commercial success.

The most common type of storage or secondary cell is the lead-sulphuric

type in which the electrolyte is dilute sulphuric acid and the

electrodes are lead plates, covered with a chemical composition known as

the active material. These plates usually consist of a lead grid, or

lattice frame in the pockets of which is pasted the active material. The

pockets or lattice bars of the plates are for the purpose of supporting

the active material which is of a weak and spongy nature. The active

material on the positive plate is usually litharge, while that on the

negative plate is red lead.

After charging, the active material on the positive plate is changed to

lead peroxide by the action of the current, and the active material on

the negative plate is changed into spongy metallic peroxide. The

composition of the active material on the plates determines the

direction of flow of the discharge, or secondary current. The current

flows from the positive plate to the negative through the external

circuit.

When fully charged, and in good condition, the positive and negative

plates may be readily distinguished by their colors, the positive plate

being a dark brown or chocolate color, and the negative a slate or grey

color.

The positive active material is hard, while the negative may be easily

cut into by the finger nail. The density of the material changes

slightly with the charge, as the material expands during the discharge.

The problem of holding the active material securely to the plates during

expansion and contraction has been a hard one to solve, each

manufacturer having some favorite form of grid or material plug to which

he pins his faith. While great improvements have been made in this

direction, it is certain that we have not yet reached perfection. Loose

active material will cause short circuits and will reduce the output of

the cell; loose active material frequently ruins a cell.

The current capacity of a storage battery depends on the area of the

plates or electrodes, and in order to increase the capacity of a

battery, and consequently the area, it is usual to use a number of

plates connected in parallel. A number of small plates of a given area

are to be preferred to two large plates of the same area, as the battery

will be of a more convenient size.

Customarily there is one more negative plate than positive, so that the

extreme end plates in a cell are negative, as the positive and negative

plates alternate with each other when assembled.

An ignition battery usually consists of two negative plates and one

positive. Cells used for power purposes have as high as sixty plates.

A single cell of storage battery should show about two volts when fairly

well charged. If more than two volts are desired more cells should be

connected in series. The total voltage will be equal to the number of

cells, in series, multiplied by the voltage per cell. The voltage per

cell should never be allowed to drop below 1.7 volts, as the cell is

likely to be destroyed when operated with a low voltage. Recharge as

soon as the voltage drops to 1.8 volts.

The ordinary six volt ignition battery consists of three separate cells

connected in series, which are encased in one protecting box.

The plates are prevented from touching each other within the cell by

means of a perforated sheet of hard rubber that is inserted in the space

between the plates. The perforations allow the liquid to circulate

between the plates.

The storage battery is furnished as standard equipment with several well

known gas engine builders, and its use is advocated by nearly all. When

used in connection with a low tension direct current magneto two

independent sources of current are at hand, either of which will ignite

the engine in an emergency.

With the magneto-storage battery combination, it is possible to obtain a

few small lights at any time, whether the engine is running or not, and

the engine is always ready to start on the first “over” with the storage

battery and a good mixture.

If a magneto is not used, difficulty is sometimes experienced in

obtaining a suitable source of charging current, as many localities do

not possess direct current plants. Batteries may be charged from the

direct current exciter in an alternating current station, or may be

charged by an alternating current rectifier such as is used by

automobile garages.

The principal objections to the storage cell are: inconvenience of

charging; sulphating of cell when standing without a charge; ease with

which the cell is ruined by short circuits; the damage caused by the

spilling of the electrolyte; and the fact that the cell gives no warning

of failing or discharged condition.

Since the composition of the plates depends on the direction in which

the current flows through the cell, it is obvious, that an alternating

current which periodically changes its direction of flow will first

charge the plates and then discharge them alternately. The result of an

attempt at charging with alternating current would be that the plates

would be in the same or a worse condition in a short space of time than

they were at the beginning. In charging a storage cell care should be

taken to determine the character of the current, especially when the

cell is to be charged from a magneto. When under charge, the cell is

connected to the charging circuit in such a way that the current flows

backwards through the cell or in a direction opposite to that when the

cell is discharging.

(86) Care of the Storage Cell.

The storage battery should never be left in an uncharged condition with

the acid electrolyte in the cell, for the solution will quickly attack

the uncharged plates and combine with them to form lead sulphate. As

lead sulphate has a high electrical resistance and is insoluble in the

electrolyte the sulphate coating will reduce the output or if present in

excess, ruin the cell. The sulphate appears as a white coating on the

surface of the plates. The only remedy for this condition at the hands

of the average engine operator is a prolonged charge, or over charge, at

a slow rate. There are several chemical processes but they are too

complicated for the average man.

As sediment collects on the bottom of the battery jars, and is liable to

cause a short circuit, the plates should be held about half an inch from

the bottom of the jar. Care should be taken that the cells of the

stationary type of battery are kept dry and clean. Do not allow dirt to

drop into the solution as it is liable to destroy the cell.

A volt meter should be used to determine the condition of the battery,

and should be used frequently. An ammeter should never be used on a

storage battery, as it is of very low resistance, and would probably

cause a rush of current that would destroy both the battery and the

instrument.

Never short circuit a storage battery, even for an instant, as excessive

current will cause the plates to buckle, or will loosen the active

material on the plates.

The plates are immersed in the electrolyte, which should cover the

entire plate or active surface. If the solution does not cover the

plate, the capacity of the cell will be reduced. Plates that are

partially covered with solution deteriorate rapidly from “sulphating.”

This is caused by the air and acid acting on the damp inactive portion

of the plate.

Usually the electrolyte consists of a dilute solution of sulphuric acid

and water, but in some ignition cells the solution is “solidified” by

some substance to about the consistency of table jelly. The object of

this thickened solution is to prevent the solution from slopping and

leaking when the battery is being transported.

The solution used in a storage battery is exceedingly corrosive in its

action, and if spilled on metal or wood will destroy it immediately.

Care should be taken in handling the electrolyte.

A cell should never be discharged below 1.7 volts for below this point,

the plates are likely sulphate. When the solution is replaced by fresh,

or water is added for the purpose of restoring the electrolyte to its

original level, use only distilled water, free from metallic salts and

suspended matter.

Many people “test” their cells by snapping a wire across the terminals

to “see if there is a good spark.” Nothing could be more injurious to

the battery, and as this test indicates nothing, the practice should be

discontinued. Make all your tests either with a hydrometer or a

voltmeter, the latter is preferable in the average case.

The electrolyte is a solution containing approximately 10% of chemically

pure sulphuric acid and 90% of distilled water. The specific gravity of

the fluid should be from 1,210 to 1,212 in all cases. A standard battery

hydrometer should be used by all storage battery users to ascertain the

exact density of the solution as the specific gravity is a direct index

to the condition of the cell. A gasoline hydrometer is useless for a

storage battery.

When mixing the electrolyte it should be placed in a glass or porcelain

jar, and the process should never be performed in the battery jar in the

presence of the plates. The solution is very active chemically and

should not be brought into contact with metallic or organic substances

because of the danger of contaminating the fluid. The acid should always

be poured into the water in a thin stream while the mixture is being

stirred with a glass or porcelain rod. Pouring the water into the acid

is likely to produce an explosion and should therefore be carefully

avoided.

As the acid heats the water during the mixing the hydrometer reading

should not be taken until the heat caused by the first addition of acid

has been reduced to that of the room. Taking a reading with a hot

solution will give inaccurate results, unless, of course, the reading is

reduced to normal by the method described in a previous chapter. When

the reading has been taken and found to be correct and the solution has

been reduced to the temperature of the room, the electrolyte may be

poured into the cell through the filler openings in the top of the cell.

Pour into each cell sufficient fluid to cover the plates but avoid

filling the cell to the top, or flooding it.

At the end of the charging time given by the maker, withdraw a sample of

the electrolyte by means of a syringe and test the specific gravity.

This should not be over 1,290 for a fully charged cell, and if the

solution exceeds this amount, pure water should be added until the

proper point is reached. Always correct the specific gravity in this way

every time the battery is charged as evaporation and internal chemical

changes cause the density to change from time to time. The voltage of a

good storage battery will be about 2.1 volts when fully charged.

Overcharging is wasteful and finally destroys the cell, the effects

being similar to those caused by excessive discharges, that is, buckled

plates and loosened active material. Overcharging a sulphated battery

may cure the trouble, a little overcharging at intervals being better

than a long continued overcharge.

An increase in the specific gravity of the electrolyte of from 30 to 50

degrees, with a corresponding rise of voltage, shows that the cell is

fully charged.

After the charging is completed remove all of the solution spilled on

the battery, preferably by washing, and wipe bone dry. If the solution

is higher in the air, remove the excess with the syringe.

(87) Make and Break System (Low Tension).

When a circuit carrying a current is opened or broken at any place in

its length, an electric spark will occur at the point at which the wires

or contacts are separated. This is due to what might be termed the

“momentum” of the current which causes it to persist in its course even

to the extent of jumping over a short distance of the highly resistant

air in the gap. The size and heat of the spark may be increased by

placing a coil of copper wire in series with the circuit that has an

iron core in the center of the turns. This coil increases the tendency

of the current to jump the gap, or in other words increases the momentum

of the circuit.

Each separation of the terminals of the circuit causes but a single

spark, so that in order to obtain another the terminals must be again

brought into contact and the current reestablished in the circuit before

the circuit is again opened. Thus the function of the make and break

igniter is to alternately make and break the circuit in the presence of

the combustible mixture. To obtain the greatest spark and most certain

ignition, the contact points should be opened with the greatest possible

speed, an action that is accomplished in the actual engine by springs

and triggers.

A typical cylindrical make and break coil consisting of an iron wire

core surrounded by a coarse copper wire core is shown by Fig. 91. At one

end of the coil will be seen the two terminal screws by which it is

connected with the circuit. Another make and break coil is shown by Fig.

92, which has the same type of winding, but differs in having the core

wire coil extended beyond the winding and heads. By closely examining

the cut, the iron wires will be seen in the projecting core tube at the

left end of the coil. A flat base is also provided for fastening it to a

stationary foundation.

A typical make and break igniter is shown by Fig. 93, together with the

usual circuit consisting of a primary coil and battery. In this figure,

A and C are the two electrodes provided with platinum contact points N

and O respectively. The electrode A is stationary and is insulated from

the iron casing K by the insulating washer H, and the insulating bushing

or tube I. The electrode C is oscillated intermittently by the engine

through its shaft E, and the trigger G, the springs S serving to snap

the platinum contact O away from N at the proper moment. This electrode

at all times, and is provided with a brass bushing F for a bearing

surface. The outer containing casing K is bolted to the combustion

chamber of the engine by the bolts LL, so that the electrodes A and C

project into the combustion chamber.

[Illustration:

Fig. 91. Kingston Cylindrical Make and Break Coil.

]

[Illustration:

Fig. 92. Kingston Make and Break Coil. Short Type.

]

Current from the battery R passes through the coil winding P to the coil

terminal U from which it passes from V to the igniter binding post J.

From J it flows along the rod D to the stationary electrode A. Since the

rod D is surrounded by the insulating washers and tube H, T and I, the

current cannot escape directly to the casing K. With the two platinum

points N and O in contact, the current flows through C to the shell K

from which point it flows back to the battery R through the conducting

path V, completing the circuit. The greater portion of the path V

consists of the engine frame. When the electrode is moved in the

direction of arrow B, the current is opened and a spark occurs at the

point of separation M, in contact with the gas in the combustion

chamber. The electrode C being connected with the engine frame is said

to be “grounded.” If the stationary electrode A were not insulated from

the casting K, the current would pass directly from the terminal J back

to the battery R without passing through the contact points at all, and

consequently no spark would be produced on the separation of the points.

[Illustration:

Fig. 93. Diagram of Igniter and Connections.

]

A push rod which is actuated by a cam on the engine, engages with the

trigger G, and causes the spark to occur when the piston is on the end

of the compression stroke. In nearly all engines, the relation between

the time of the spark and the piston position can be regulated to suit

the requirements for advance and retard. This adjustment is necessary in

order that the spark may be varied to meet the difference between the

starting and running requirements.

While the ignition should be considerably advanced while running, it is

necessary to retard it when starting, as the engine is liable to “kick

back” with an advanced spark.

This advance and retard device should be accessible while the engine is

running, and the operator should be able to control the point of

ignition at all times. Many men have been seriously injured by the lack

of this device or by neglecting to use it.

The contact points make contact only for a short time before the spark

is required in order to reduce the amount of current to the minimum, and

therefore increase the life of the batteries.

The duration of the “make” or contact should be as short as possible.

Prolonged contact weakens the batteries and causes them to run down

rapidly. For the same reason the electrodes should remain separated

until the make is actually required.

A certain period of contact is necessary, however, to allow the spark

coil to “build up,” but with a properly designed coil the time required

is very short.

Some engines provide a device that cuts out the ignition current

altogether during the idle strokes. This adds materially to the life of

the batteries.

The igniter should be located near the inlet valve, as the cold incoming

gases tend to keep it cool and clean, besides insuring the presence of

combustible gas around the igniter electrodes. Improper placing of the

igniter will greatly reduce the efficiency of the engine. Avoid placing

the igniter in a pocket, or in the path of the exhaust gases.

The make and break ignition system has many good features, but cannot

successfully be applied to engines running over 500 revolutions per

minute, nor can it be applied to engines of less than 3 H. P. as the

parts would be too small and delicate to be durable.

The make and break igniter produces the largest and “hottest” spark of

any type of ignition, and is especially desirable for large or slow

running engines. Being operated at a low voltage, it is not as easily

affected by moisture, poor insulation, or dirt as the high tension or

jump spark system, nor is it liable to give the operator such a violent

“shock.”

Engines governing by the “hit and miss” system have a device that cuts

out the current during the “missed” power strokes. This effects a

considerable saving in battery current, especially on light loads when

the engine misses a great number of strokes.

While possessing many points of merit, the make and break system is open

to several serious objections:

1. Due to the high combustion temperature there is excessive wear of the

working parts in the cylinder, this wear causes a change in the ignition

timing.

2. The low voltage used in the make and break system calls for perfect

contact of the electrodes in the cylinder. This contact is often

interfered with or entirely prevented by the accumulation of carbonized

oil and soot deposited on the surfaces.

3. The wear of the operating spindle or shaft, which passes through the

cylinder wall causes leakage, which in turn causes a loss of compression

in the cylinder.

4. The wear of the external operating mechanism produces a change in the

timing. The edge of the fingers, wiper blades, etc., tend to cause an

advance in the ignition as a general rule, with the attendant danger of

broken crank shafts.

5. The system is mechanically complicated, correct operation calling for

constant care as to adjustment.

All ignition apparatus wears in the course of time and changes the

timing of the engine. The electrodes and push-rods wear and require

readjustment. Generally the tendency of worn parts is to advance the

ignition. This change in timing occurs so gradually that the operator

does not notice it until the engine begins to pound, or until the

efficiency has been considerably reduced.

When the engine is new it is well to mark the ignition mechanism in such

a way that the relative positions of the crank and igniter will be shown

at the time when the igniter trips. It will then be possible for the

operator to refer to the marks at any time to tell whether his ignition

is occurring at the proper time. Always mark the half-time gears when

taking the engine apart for the difference of one tooth when

reassembling will be sufficient to throw the engine out of time.

The usual method of marking the gears, is to center punch, or scratch

one tooth on the small gear, and then mark the two teeth of the large

gear that lie on either side of it. With these marks it is possible to

replace the gears in their original and proper positions.

The igniter should trip, causing the electrodes to separate just before

the end of the compression stroke is reached, or just before the crank

reaches the inner dead center. The distance lacking the exact dead

center represents the instant of time between the time of ignition and

the actual pressure established by the combustion.

As most engines have the ignition considerably retarded when starting,

the igniter will trip later with the lever in the “start” position than

when in the “running” position. Never fail to retard spark when starting

nor forget to advance it when engine is up to speed.

The actual advance given to an engine depends on the character of the

fuel and on the speed.

An engine is said to have an advance of 10°, if the crank lacks 10° of

having made the inner dead center at the time of ignition.

The most economical point of ignition is easily determined when the

engine is running on a steady load, by varying the point of ignition and

noting the position assumed by the governor.

(88) Operation of the Make and Break Igniter.

To keep the igniter in order, and to obtain the best results with the

least trouble, the following hints should be observed:

(1) Clean the igniter frequently, and remove all deposits of oil and

carbon. For cleaning, the igniter must be removed from the cylinder,

care being taken to avoid injury to the packing or gasket. Graphite

dusted on the gasket will prevent it from sticking to either the igniter

or cylinder.

(2) If the contact points are rough, pitted, or covered with a carbon

deposit, the scale should be removed, and the points smoothed down with

a fine file, taking care that the two faces are filed parallel with one

another.

(3) Insulating washers and tubes should be removed and washed in

gasoline. The hole through which the igniter rod passes should be

scraped free from any deposit for much trouble can be caused by a tight

working shaft.

(4) Examine the hole or bushing through which operating spindle passes,

for wear. A worn spindle or bushing may cause a serious loss of

compression; replace worn bushing at once.

See that the insulation of the stationary electrode is not broken. If it

is injured in the slightest degree, replace it with new.

(5) Often the sparking points may be cleaned temporarily without

removing the igniter from the cylinder by pulling upon the outside

finger or trigger until the points come together, and then pushing in

towards the cylinder several times on the movable electrode, which

slides them one on the other, scraping off the deposit. This method is

only a make shift.

(6) After removing igniter, replace all wires, screwing them firmly into

place. The ends of wires and connecting screws should be perfectly clean

when the connection is made; to insure perfect contact, the surfaces

should be scraped or sand-papered until bright and shining. See that no

foreign matter of any kind gets between the wires and the metal of the

binding screws. Wherever possible connections should be soldered.

(7) A small coil of the wire should be made at the point of connection;

i. e., the wire should be a trifle longer than necessary to reach the

binding screw, the excess wire being coiled up on a pencil. This coil

allows of removing igniter, allows for broken wire ends and reduces the

tendency to loosen the connection.

(8) Ground wires, or wires connected with the frame of the engine should

receive careful attention. They are generally fastened under some screw

or bolt on the engine which may become loose or fail to make contact,

thus opening the entire circuit and causing the engine to stop. The

ground wires are generally connected in inaccessible places, and require

all the more attention for this reason.

(9) For the primary of low tension wiring, use only the best grade of

stranded rubber covered wire. A special wire for ignition purposes is on

the market. It is rather expensive but is just the thing for the

service.

Never use cotton covered or waxed wire. This covering affords absolutely

no protection against moisture or abrasion.

(10) As the voltage of a primary circuit, or circuit for make and break

is very low, and the current comparatively high, it is well to have the

copper as large as possible. It should never be less than number 14

gauge. Don’t use solid wire if you can obtain stranded conductor.

(Stranded wire is made up of a number of fine wires which are twisted

into a cable or rope of the desired size.)

(11) Oil destroys rubber insulation and should be kept off the wiring.

Try to locate the conductors so that they will be out of range of oil

thrown by the moving parts.

(89) Jump Spark System (High Tension System).

Due to its simplicity and the light weight of its moving parts, the high

tension ignition system is applied to practically all small, high speed

engines running 500 R.P.M. or over. The high tension system is also

desirable from the fact that it has no moving parts in the cylinder of

the engine.

The principal objection to the high tension system is the ease with

which the high voltage current leaks or short circuits, moisture being

fatal to the operation of a jump spark engine.

Instead of producing the spark by breaking the circuit of a low tension

current, the spark is produced by increasing the voltage to such a point

that the current will jump directly across a fixed gap. To cause the

current to jump through the air requires an extremely high voltage, and

as the battery current is very low it is necessary to introduce a device

known as a “transformer” to stop the current up to the required tension.

In addition to the voltage required at atmospheric pressure (about

50,000 volt per inch of spark) we must also furnish sufficient pressure

to overcome the increased resistance due to the compression in the

cylinder.

Unlike the spark coil used on the low tension make and break system, the

induction coil or transformer coil has two separate and distinct coils,

that are thoroughly insulated from each other. One coil has a few turns

of heavy copper wire which is called the primary. The other consists of

many thousands of turns of very fine copper wire, and is called the

secondary. Both coils are wound around a bundle of soft iron wire called

the core, from which they are carefully insulated. When a battery or

magneto current flows through the primary coil, the core is magnetized,

and throws its magnetic influence through the turns of the secondary

coil.

In Fig. 94 the primary coil and the low tension battery and magneto

circuit are represented by heavy lines. The secondary coil, and high

tension circuit are represented by light lines.

In order to obtain a continuous discharge of sparks it is necessary to

make and break the current in the primary coil very rapidly. This is

done by means of the interrupter or vibrator, which is indicated in the

diagram by V. The interrupter consists ordinarily of a spring A on which

is fastened a soft iron disc D and a platinum contact point B. When the

core is magnetized it attracts the iron disc D which is pulled toward

the core, bending the spring A and breaking the contact between the

platinum point B and C. When the contact points are separated, and the

current broken, the core loses its magnetism, and the spring assumes its

normal position, which brings the platinum points B and C into contact

once more, and reestablishes the current through the primary. The core

is again magnetized and the primary current is again broken, and so on.

This make and break of the current is thus accomplished automatically,

the current being broken many thousands of times per minute, the

vibrator moving so fast as to cause a continuous hum.

As soon as the current starts flowing, the magnetic force spreads out

through the secondary coil and threads through the turns of which it is

composed. The instant that the current ceases, the magnetic force

decreases and the turns are again threaded by the magnetic field on its

return to the core.

Thus two magnetic waves are sent through the secondary coil, one when

the circuit is “made,” and one when the circuit is “broken.”

[Illustration:

Fig. 94. Diagram of High Tension Coil.

]

When a magnetic wave threads or spreads through the turns of a coil of

wire, a current of electricity is generated in the coil, the quantity

and pressure or voltage of which is proportional to the intensity of the

magnetism, and to the number of turns of wire in the secondary coil.

Thus it will be seen that at every make and break of the low tension

current in the primary coil, a current is generated in the secondary. As

the voltage generated in the secondary is roughly proportional to the

number of turns in the secondary, and as there are many thousands of

turns, it is evident that the voltage in the secondary will be very

high. Thus by the use of the induction coil, the low tension battery

current is transformed into a high tension current of sufficient voltage

to break down the high resistance of the spark gap.

The condenser is shown at L which has one wire leading to the vibrator

spring A, and one wire to the contact screw M. The function of the

condenser is to absorb the spark produced at the vibrator points so that

the break is made quickly, producing a maximum spark. The intensity of

the spark depends upon the quickness with which the primary current is

broken, and if it were not for the condenser the length and intensity of

the spark would be greatly reduced. This device consists of alternate

layers of paper and tin foil, every other leaf of foil being alternately

connected to the vibrator spring and to the contact screw.

A method of using two independent sets of battery is shown in the

diagram, so that either set may be thrown into circuit by means of the

double throw switch O. When handle J is in contact with E, the current

of battery set H flows through the coil as shown by the arrows. When J

is in contact with F, the battery C is thrown into circuit. The spark

gap is shown by X, which represents the spark plug in the cylinder.

In practice, the portion of the circuit shown by I-U is generally formed

by the frame of the engine, or is grounded. The terminal P of the high

tension circuit is always grounded through the threaded shell of the

spark plug, the grounded circuit being shown by the dotted lines.

Grounding saves wire and many connections, for with P and U connected to

ground it follows that one binding post will serve the place of one high

tension and one primary post, making three coil connections instead of

four.

In order that the spark will occur in the cylinder of the engine at the

proper time, a switch must be placed in the primary circuit of the coil,

that will open and close the circuit at proper intervals. Such a switch

is called a timer, and is always driven by the engine. The timer is

connected to the engine shaft in such a way that contact is made at, or

slightly before, the time at which the explosion is required, and as

soon as possible after spark occurs the current is cut off.

For multiple cylinder engines it is usual to provide one coil for each

cylinder, the primaries of which are controlled by a single timer and

battery. A high tension wire from each coil runs to the corresponding

cylinder. Instead of having a number of coils with a battery system,

there are two or three makes that operate with one coil in combination

with a special device known as a distributor which controls the high

tension current. The high tension distributor directs the current to the

proper cylinder that is in the order of firing, the timing being

performed by a timer similar to that used with multiple coils except

that a single contact sequent is supplied.

(90) Vibrator Construction.

Since the efficiency of the high tension coil depends largely on the

construction and efficiency of the vibrator, the different coil makers

have developed various types of vibrators that differ greatly from the

simple device shown in the coil diagram in details.

[Illustration:

Fig. 95. Kingston Vibrator.

]

The main objects in view in the construction of a successful vibrator

are:

1. To reduce the weight of the moving part as much as possible in order

to increase the speed of vibration, and to make the trembler instantly

responsive to the timer.

2. To cause the contact points to separate as rapidly as possible in

order to cause the maximum spark.

3. To have the contacts as hard and infusible as possible to resist wear

and the action of the spark between the contacts.

4. To make any adjustments that may be required, due to wear, as simple

and accessible as possible.

The types of vibrators are legion, and we have not the space to go into

the details of all the prominent makes, but will illustrate and describe

two well known types.

The Kingston vibrator made by the Kokomo Electric Company, is a good

example of a modern vibrator and is shown in detail by Fig. 95. All

adjustments between the contact points are made by means of the contact

screw A which carries a platinum point at its inner end. The retaining

spring D keeps the contact screw from being jarred out of place by the

engine vibration, without the use of lock nuts. Turning A against the

vibrator, the tension of the spring B is increased, raising the screw

decreases the tension. Increasing the tension screw increases the length

and heat of the spark, and also increases the current consumption. At N

is a separate thin iron plate which is acted on by the magnetized core,

a rivet fastening the plate to the main vibrator spring is shown at the

end of the spring. The current enters through the lug C, and from this

point the circuit is the same as shown in the coil diagram.

(91) Operation of the Jump Spark Coil.

The spark produced by a coil in good condition should be blue-white with

a small pinkish flame surrounding it, when the gap is ¼ of an inch or

less. The sparks should pass in a continuous stream with this length of

gap without irregular stopping and starting of the vibrator. Coils

giving a sputtering, weak discharge that causes sparks to fly in all

directions are broken down and should be remedied.

The secondary windings of coils are often punctured or broken down by

operating the coil with the high tension circuit open, or by trying to

cause long sparks by increasing the spark gap over ⅜ of an inch in the

open air. Coils are also broken down by allowing excessive currents to

flow in the primary coil. Never cause a spark to jump over ⅜ of an inch.

High compression in the cylinder shortens the jumping distance of a high

tension spark. Coils that will cause a stream of sparks to flow across a

gap of ½ an inch in the open air are often unable to cause a single

spark to jump a gap of 1/32 of an inch under a compression of 80 pounds

per square inch in the cylinder.

Remember that a hot spark causes rapid combustion, and will fire a

greater range of mixtures and “leaner” charges, than a straggling, thin,

weak spark. Spark coils that give poor results with a long spark gap

under high compression are often benefited by the shortening of the

spark gap. Shortening the gap will increase the heat of the spark, and

will insure the passing of a spark each time that the timer makes

contact. A good coil should have no difficulty in igniting a piece of

paper inserted between the wires forming the spark gap in the open air.

[Illustration:

Fig. 96. Kingston Dash Coil.

]

The adjusting screw affords a means of increasing or decreasing the

tension of the vibrator spring, and the amount of battery or magneto

current flowing through the primary coil. Increasing the tension of the

spring requires stronger magnetization of the core to break the circuit

of the contact points. This in turn calls for more current from the

battery; hence in order to lessen the demand for current on the battery,

the tension should be as little as possible to obtain the necessary

spark. An increased tension produces more spark as the magnetization of

the core is increased, but for the sake of your batteries decrease the

tension as much as possible with a satisfactory spark.

Almost all operators have a tendency to run with too stiff a vibrator,

and hence use too much current. An efficient coil should develop a

satisfactory spark with ¼ to ½ of an ampere of current in the primary

coil. I have often found coils that would work well with ½ ampere, that

were screwed up so tight that the coils were consuming 4 to 5 amperes or

8 to 10 times as much as they should.

A battery ammeter used for testing the current consumed by coil will

save its cost many times over in batteries and burnt points if used at

frequent intervals in the primary circuit.

An automobile or marine engine should be tested for vibrator adjustment

in the following way:

Adjust vibrator so that spring is rather stiff. Start engine and get it

thoroughly warmed up and running at full speed, then slowly and

gradually decrease the tension of the spring until misfiring starts in;

then slowly increase tension until misfiring stops. Increase the tension

no farther; this is the correct adjustment.

Poor vibrator adjustment is the cause of much trouble and expense as it

uses up the batteries and wastes fuel. The principles of correct

adjustment are simple, the adjustment easily made, and there is no

possible excuse for the high current consumption and rapid battery

deterioration met in every day practice. The usual practice of the

average operator is to tighten the vibrator until the spark (observed in

the open air) is at its maximum. This is commonly known as “adjusting

the coil;” shortly after you hear of him throwing out his batteries as

no good. After once getting the vibrator in proper trim the ear will

give much information as to the adjustment.

A vibrator adjusted too lightly will cause “skipping” or misfiring with

the consequent loss of power.

Never attempt to operate a coil that is damp; the coil will be ruined

beyond repair. Above all, do not place the coil in a hot oven to dry, as

the box is filled with wax, and if this is melted it will run out and

reduce the insulation of the coil. Dry coil gradually.

If the batteries are new or too strong the vibrator may be held against

the core of the coil so that the vibrator will not buzz. If this is the

case loosen the screw until it works at the proper speed. If the

batteries are weak, the coil may not be magnetized sufficiently to draw

the vibrator and break the circuit. If this is the case tighten the

screw. If the vibrator refuses to work with the battery and wiring in

good condition, and if you are sure that the current reaches the coil,

look for dirty or pitted contacts on the vibrator.

Should the contact points be dirty, clean them thoroughly by scraping

with a knife or sandpaper. Water on the points will stop the vibrator,

as will oil or grease.

If contact points are of a uniform gray color on their contact surfaces,

and are smooth and flat without holes, pits or raised points, they are

in good condition. If pits, discolorations or projections are noted, the

contact surfaces should be brought to a square, even bearing by means of

a small, fine file. The point should not come into contact on an edge,

but should bear on each other over their entire surface. Do not use sand

paper to remove pitting, as it is almost impossible to secure an even,

flat surface by this means.

It is best to remove the contact screw and vibrator blade for

examination and cleaning, as it is much easier to file the points square

and straight when removed from the coil.

Be careful not to bend the vibrator spring when cleaning, as the

adjustment will be impaired. When replacing contact screw and vibrator

blade in coil, be careful that they are in exactly the same relative

position as they were before removing. Also be sure that the contacts

meet and bear uniformly on their surfaces.

(92) Primary Timer.

The duty of the primary timer is to close the primary circuit of the

spark coil at, or a little before the time at which the explosive of the

charge is required. The exact time at which the timer closes the circuit

depends on the load, the speed, and the nature of the fuel. The lapse of

time between the instant that the timer closes the circuit and the

instant at which the piston reaches the end of the compression stroke is

called the “advance” of the timer. When the timer closes the circuit

after the piston reaches the end of the stroke, the timer is said to be

“retarded.” The timer is constructed so that the time of ignition or the

advance and retard can be varied between wide limits. Advancing the

spark too far will cause hammering and power loss as the piston will

work against the pressure of the explosion.

Retarding the spark will cause a loss of power, as the compression will

be less when the piston starts on the outward stroke; and also for the

reason that more of the heat will be given up to the cylinder walls as

the combustion will be slower. The pressure in the cylinder is less with

retarded ignition. Greatly retarded ignition often causes overheating of

the cylinder walls, especially with air cooled engines, and also

overheats and destroys the seat and valve stem of the exhaust valve. Do

not expect the engine to develop its rated horse-power or run

efficiently with a late, or retarded spark.

When the engine is installed, and before the timer wears or has a chance

to get out of adjustment, look it over carefully and see whether the

maker has left any marks relating to the timing of the spark. If there

are no marks, it is well to determine the relation between the position

of the piston and the timer, as the efficiency of the engine depends to

a great degree upon the firing point.

Timers are advanced and retarded by partially rotating the housing

either in one direction or the other. When the timer is mounted directly

on the cam shaft with the cam shaft traveling in a direction opposite to

that of the crank shaft, the timer will be retarded by moving it in the

same direction as the cam shaft travels, moving it against cam shaft

rotation advances the spark.

Timers for two stroke cycle engines rotate at crank shaft speed, and the

direction of advance and retard varies with the methods adopted for

driving the timer.

(93) Timer Construction.

Fig. 97 shows a typical timer and circuit arranged for a four cylinder

engine. The device can be arranged for any number of cylinders, however,

by changing the number of sectors, the sectors being equal to the number

of cylinders. There are timers on the market that differ from the one

shown in the diagram but the principle of operation is the same with

all. The shaft E is usually connected to the cam shaft and is

electrically grounded to the engine frame at L by means of the bearing

in which the shaft rotates.

The lever F mounted on the shaft E carries the pivoted arm H which is

free to move on the pivot to a limited extent to allow for wear on the

walls W-W-W-W. At one extremity of H is the roller I which rotates on

the pin J, as the roller runs around W-W-W-W. At the other extremity of

H is fastened the spring S, which forces I into contact with the walls.

A-B-C-D are metallic contact sectors whose connections lead to the four

spark coils.

When the metal roller I comes into contact with one of the sectors as at

B, the sector is grounded to the engine frame by the roller, the current

traveling through the roller and its pin, through lever H and its pin,

through the lever F and shaft E to ground at L, the course of the

current being indicated by the arrows.

[Illustration:

Fig. 97. Timer Diagram.

]

As the shaft E rotates and carries with it roller I, the roller makes

contact with the sectors in order B-C-D-A, if rotated in the direction

shown by arrow, which rotation grounds the primary coils of the spark

coils R^3-R^4-R^1-R^2 in succession; the connection from the timer to

the primary being to the primary binding posts P^3-P^4-P^1-P^2. A high

tension spark occurs at each contact of the roller with the sectors, as

the contact allows current to flow through the primary of the coils. The

high tension binding posts S^1-S^2-S^3-S^4 are connected with the spark

plugs or spark gaps U^1-U^2-U^3-U^4 by means of high tension cables. As

soon as the timer grounds a coil, the coil produces a high tension spark

in its corresponding spark plug.

It is evident from the foregoing that the timer not only determines the

time at which a spark will take place, but it also determines the

cylinder in which the spark will be produced, providing of course that a

spark coil is provided for each cylinder.

The contact sectors A-B-C-D are insulated from each other by the

insulating walls W-W-W-W, the inner surface of which provides a path on

which the contact roller I revolves.

The contact sectors and insulating walls are encased by the protective

housing Z, to which they are rigidly fastened.

The housing Z can be moved back and forth on the shaft E for advance and

retard, by means of the lever K.

The current flows from the battery terminal V (with the roller in the

position shown) through the switch M, through coil R^3, post P^3 to

sector B, from which it passes through the roller I, levers H and F to

ground. From the ground on the engine frame the current flows back to

its source, the battery O, thus completing the circuit. When the roller

makes contact with sector C, the coil R^4 is energized, contact with D

energizes R^1, and so on. No two coils can be thrown on simultaneously

as only one coil is grounded at a time. The high tension current flows

from each coil to its plug as soon as the current passes through the

primary of that coil.

In some timers, the current is taken from the revolving arm through a

separate connection to ground instead of grounding the shaft through the

bearings. With these timers, the connection is not affected by worn

bearings or an oil film that tends to insulate the shaft from the

bearings.

(94) Operation of Timers.

Timers frequently cause misfiring which is generally due to dirt or oil

getting between the contacts, or to the wear of the insulating walls

W-W-W-W, or to the wear of the moving parts.

Dirt or gummy oil will prevent the contact coming together and

completing the circuit, or will clog up the rollers or levers so that

they cannot perform their functions properly. This will of course

interfere with production of the spark.

The contacts and moving parts of the timer should be kept as clean as

possible, all dirt and heavy oil being removed by means of gasoline at

regular periods. Make a practice of cleaning out the timer at intervals

not greater than one month; oftener if possible.

Parts subject to wear, such as the roller pin J and the bearings should

be well lubricated, none but the lightest oil being employed for this

purpose. Heavy grease will gum the contacts and cause trouble. There

should be no rough places or shoulders on the contact sectors or on the

walls W-W-W-W as roughness will cause the roller to jump over the high

places which in turn result in misfiring. The remedy is to machine the

surfaces of the sectors and walls by grinding or turning in the lathe.

Care should be taken in this operation to have the interior perfectly

smooth and the sectors perfectly flush with the walls. Repair black or

burnt sectors immediately by grinding or sand paper.

Burnt spots or blackened surface on the contact sectors prevent good

contact between roller and sector, sectors should show a bright, shining

metallic surface.

Sometimes the insulation warps or swells above the contacts so that the

roller jumps over the contacts without touching them, or if for any

reason that contact is made under these conditions, it is of a short

period and results in a poor spark.

Timers often make good contact when starting, or at low speed, and

misfire badly at high speed. This will be caused generally by the

contact sectors or insulation projecting beyond one another, the roller

has time to make good contact at low speed but jumps over the sector at

high.

The roller I may become rough or develop a flat stop which will cause it

to jump over the contact occasionally, or it may become loose on its

bearing pin J, causing intermittent misfiring.

The wearing or loosening of pins J and X result in poor contact. Should

pin J fall out of the lever H, the roller would drop out of the fork and

cause serious damage. This has happened in two cases to my knowledge.

Should the spring G weaken or break, contact will be made intermittently

at high speed, and no contact at low. In this case it would probably be

impossible to start the engine. In case the spring breaks, a rubber band

may be used temporarily. Wire connections to the timer should be

examined frequently as the continual back and forth movement tends to

twist and loosen the wire. Use stranded or flexible wire for these

connections, if possible.

Before removing the timer mark the hub and the shaft so that the hub can

be properly replaced. If this is not done the engine will be out of time

with the usual results of hammering or power loss.

Should the gears which drive timer shaft be removed, be sure and mark

the teeth of both gears in such a manner that there will be no mistake

possible in reassembling them. Mark a tooth on the small gear by

scratching or with a center punch (the tooth selected should be in mesh

with the large gear). Then mark the two teeth of the large gear that lay

on either side of the marked tooth of the small gear. Thus it will be

easy to locate the proper relative position of the two gears at any

time.

(95) High Tension Spark Plug.

The high tension spark plug is a device that introduces the spark gap

and spark into the combustion chamber, and at the same time insulates

the current carrying conductor from the cylinder walls. Since the

voltage of the jump spark current is very high it is evident that the

insulation of the plugs must be of a very high order and that this

insulation must be capable of withstanding the high temperature of the

combustion chamber. A cross-section of a typical plug is shown by Fig.

98, together with its connections and the course of the current, the

latter being shown by the arrow heads.

The electrode B through which the current enters the cylinder is

thoroughly insulated from the walls by the porcelain rod C.

The porcelain forms a gas tight joint with the threaded metal bushing F

at the point P, the tension caused by the electrode B and the nut I

holds the porcelain firmly on its seat at P.

The nut is supported by the porcelain shell H which rests in the top of

the metal bushing F. A washer L is inserted between H and F to insure

against the leakage of gas from the plug should a leak develop at P. L

being a soft washer (usually asbestos) allows the porcelains C and H to

expand and contract without breaking. A packing washer or gasket is also

placed at the point where the electrode B passes through the porcelain

H. This is the washer Q, held in position by the nut I. This washer is

elastic and reduces strain on porcelain caused by the expansion.

The cylinder wall G has a threaded opening R into which the plug is

screwed, the threads of the opening corresponding with the threads on

the metal sleeve E. The plug may be removed from the cylinder for

examination without disturbing the adjustment of the electrode and

porcelains by unscrewing it at R.

Allowing the current to jump from the electrode to the cylinder wall via

the metal sleeve saves one wire and connection, the cylinder and the

frame of the engine serving as a return path for the current. This

simplifies the wiring and minimizes the danger of high tension short

circuits.

[Illustration:

Fig. 98. Cross-Section of Typical Spark Plug.

]

By unscrewing the threaded metal bushing F it is possible to examine the

condition of the porcelain rod C at the point where it is exposed to the

heat of the cylinder. This inspection can be made without disturbing the

packed joints at L or Q.

In the high tension, or jump spark system, the spark gap D-K is of fixed

length, hence there are no moving parts or contacts within the cylinder

to wear, to cause leakage of gas, or to cause a change in the timing.

This advantage is offset to some degree by the difficulty experienced in

maintaining the insulation of the high tension current.

The high tension current leaves the spark coil M at the binding screw N,

flows along the wire J, and enters the spark plug at the binding screw

A. From the binding post the current follows the central electrode B to

its terminal at D. At D a break in the circuit occurs which is called

the spark gap. It is at this point that the spark occurs, the current

jumping from D to point K through the air. Point K is fastened in the

threaded metal sleeve E which is in turn screwed into the cylinder wall

G or ground. From the ground the current returns to its source through

binding post O to the coil. The spark therefore occurs inside of the

cylinder wall and in contact with the combustible charge, at the point

marked “spark” in the cut.

[Illustration:

Fig. 99. Bosch Spark Plugs.

]

If the fuel, lubricating oil, and air are not supplied in proper

proportions, soot will be deposited on the lower surface of the

porcelain, and as soot is an excellent conductor of high tension

current, the current will follow the soot rather than the high

resistance of the spark gap, a condition that will result in misfiring

or a complete stoppage of the motor. Carbonized lubricating oil or

moisture have the same effect.

Preventing the deposits of soot, moisture and carbonized oil is the

chief object of plug manufacturers, many of whom have brought out

designs of merit. In fact the problem of elimination of soot is the

principal cause of the many types of plugs now on the market.

While many plugs differ in minor refinement of detail from the typical

plug shown, the connections and general construction are the same in all

types, the spark being produced in a gap of fixed length which is

insulated from the cylinder.

A well known form of plug, the Bosch, is shown by Fig. 99 a-b. In this

plug a special material known as Steatite is used instead of the usual

porcelain. The three external electrodes surrounding the center

electrode is a particularly efficient arrangement, especially for

magnetos. A peculiar form of pocket minimizes the soot problem.

As porcelain is brittle and is easily broken by the effects of heat or

blows, mica insulation is often used in place of the porcelain. The

central core of a mica plug is formed by a stack of mica washers, which

are held in place by the central electrode and the upper lock nuts.

A poorly constructed mica plug is easily destroyed by a weak,

stretching, electrode, or by an overheated cylinder. The latter causing

the washers to shrink and admit oil between the layers of mica washers

causes a short circuit. As soon as the mica washers loosen and separate,

they should be forced together by means of the mica lock nuts on the top

of the plug.

If by any reason the mica core becomes saturated with oil, it is best to

obtain a new one, as it is almost impossible to remove the oil by simple

means open to the average operator.

The chief value of a mica plug lies in its toughness and mechanical

strength, a good mica plug being practically indestructible.

When heated, porcelain does not expand at the same rate as the metal

sleeves, hence in poorly designed or imperfect plugs, heavy strains are

thrown on the delicate porcelains which causes them to crack. When a

crack develops it provides a lodging place for soot and carbon which of

course causes a short circuit. Should a compression leak occur through

faulty packing between the porcelain and sleeve, it should be

immediately tightened up for eventually it will leak enough to destroy

the plug or reduce the output of the engine.

When ordering a plug be sure that you know the size and type required by

your engine. Some engines require a longer plug to reach the combustion

chamber than others. Never install a shorter plug than that originally

furnished with the engine. Be sure that the plug is not too long as it

may interfere with the action of the valves or may be damaged by them.

Plugs are furnished with several threads and taps, i. e.:

½ inch pipe thread (Generally used on stationary engines).

Metric Thread (Generally used on imported autos).

⅞ inch A. L. A. M. Standard (Used on Domestic automobiles).

Using a plug in a hole tapped with the wrong thread will destroy the

thread in the cylinder casting and cause compression leaks.

(96) Care of Spark Plug.

Porcelains are often broken by screwing the plug too tightly in a cold

cylinder, as the cylinder expands when heated and crushes the frail

plug. A plug installed in this manner is difficult to remove as the

expanded walls grip the thread. The plug should be screwed in just

enough to prevent the leakage of gas. A short thin wrench should be used

in screwing the plug home such as a bicycle wrench. A wrench of this

type is so short that it will be almost impossible to exert too much

force, and will be thin enough to avoid any possible injury to the

packing nut. Bad leaks may be detected by a hissing sound that is in

step with the speed of the engine, small leaks may be detected by

pouring a few drops of water around the joint. If a leak exists bubbles

will pass up through the water and show its location.

Plugs are more easily removed from a cold cylinder than a hot. If the

plug sticks when the engine is cold and is impossible to remove with a

moderate pressure on the wrench squirt a few drops of kerosene around

the threads. Never exert any force on the porcelain or insulation. The

high tension cables should be connected to the plugs by means of some

type of “Snap Terminal,” such terminals may be had from automobile

dealers.

These terminals make a firm contact with the plug and do not jar loose

from the plug by the vibration of the engine. They are easily

disconnected when the inspection of the plug becomes necessary, and are

generally a most desirable attachment.

The high tension cable should be firmly connected to the plug terminal

under all circumstances. A loose connection will cause misfiring or will

bring the engine to an abrupt halt. If snap terminals are not used the

plug binding screw should be screwed down tightly on the wire. When

making connections see that the wire is bright and clean, and that

frayed ends of the wire do not project beyond the plug and make contact

with other parts of the engine.

A large percentage of high tension ignition troubles are due to short

circuits in the spark plug which are generally caused by deposits on the

surface of the plug insulation. Soot or oil may be removed from the plug

by scrubbing the porcelain and the interior of the chamber with gasoline

applied by a tooth brush. Examine the plug for cracks, and if any are

found, replace the porcelain or throw the plug away. A cracked porcelain

is always a cause of trouble.

To test a plug for short circuits, remove it from the cylinder,

reconnect the wire, and lay the sleeve of the plug on some bright metal

part of the engine in such a way that only the threaded portion is in

contact with the metal of the engine. Close the switch and see if sparks

pass through the gap. If no sparks appear, and if the coil is operating

properly, clean the plug. As an additional test for the condition of the

coil, hold the end of the high tension cable about ¼ inch from the metal

of the engine while the coil is operating. If a heavy discharge of

sparks takes place between the end of the cable and the metal of the

engine, the coil is in good condition.

If a partial short circuit exists, the spark at the gap will be weak and

without heat; the result will be intermittent, or misfiring with a loss

of power. Moisture in the cylinder is a common cause of plug short

circuits, the moisture coming from leaks in the water jacket or from the

condensation of gases in a cold cylinder. A drop of water may bridge the

spark gap, allowing the current to flow from one electrode to the other

without causing a spark.

If a cloud of bluish white smoke has been issuing from the exhaust pipe

before the misfiring started, you will probably find that the trouble is

due to sooted or short circuited plug.

The remedy is to decrease the amount of lubricating oil fed to the

cylinder.

When a magneto is used the intense heat of the spark causes minute

particles of metal to be torn from the electrodes and deposited on the

insulation as a fine metallic dust. This will of course cause a short

circuit and must be removed. Short circuits are sometimes caused by the

magneto current melting the electrodes and dropping small beads of the

metal between the conductors. All metallic particles should be removed

from the plug.

While a spark plug may show a fair spark in the open air test, it will

not always produce a satisfactory spark in the cylinder on account of

the increased resistance of the spark gap due to compression.

Compression increases the resistance of the spark gap enormously and

thin, highly resisting carbon films that would cause very little leakage

in the open air will entirely short circuit the gap under high pressure,

the current taking the easiest path which in the latter case is the

carbon deposit.

In order to produce conditions in the open air test similar to those in

the cylinder we must devise some method of increasing the resistance of

the spark gap in the open air above any possible resistance that could

be offered by the carbon film.

Placing a sheet of mica or hard rubber between the electrodes, or in the

spark gap, will increase the resistance to the required degree. If the

spark plug is in good condition the spark will jump from the insulated

terminal to the shell when the mica is in the spark gap, but if a short

circuit exists the current will go through it without causing a spark.

It is assumed that the battery and coil are in good condition when

making the above test.

If the electrodes or spark points are dirty they should be cleaned with

fine sand paper, special attention being paid to the surfaces from which

the spark issues. When reassembling the plug, see that all of the

washers and gaskets are replaced and that the length of the spark gap is

unchanged. A little change in the spark gap may make a great change in

the spark. A good spark is blue white with a faint reddish flame

surrounding it. When the discharge is intermittent or sputters in all

directions, either the coil or the plug are partially short circuited.

Always have a spare plug on hand.

Ordinarily the length of the gap or the distance between the electrodes

should be about 1/32 inch for batteries, and a trifle less for magnetos.

A silver dime is a good gauge for the gap. If the engine misfires with

the coil and batteries in good condition, try the effects of shortening

the gap a trifle, usually this will remedy the difficulty. Exhausted

batteries may be made operative temporarily by closing up the plug gap

to 1/64 inch or even less. Shortening the gap increases the heat of the

spark and nothing is gained by having it over 1/32 inch.

Almost all high tension magnetos have visible safety spark gaps that

show instantly the presence of an open circuit in the secondary or high

tension circuit. If an open circuit exists, a stream of sparks will flow

across the safety spark gap at low speed.

To determine the cylinder that is misfiring in a four cylinder engine

proceed as follows:

Remove cover on spark coil, and hold down one vibrator spring firmly

against the core while the engine is running.

If the engine speed is not decreased by cutting this coil out of action,

it is probable that this is the coil connected to the misfiring

cylinder. Now release this vibrator and proceed to the next coil, and

hold its vibrator down. If this decreases the speed of the engine you

may be sure that the first coil is in the defective circuit. If the

vibrator buzzes on the coil under inspection the trouble will be found

in the plug.

Cutting out a coil connected to an active cylinder decreases the speed

of the engine. Cutting out the coil connected with a dead cylinder makes

no difference.

(97) Magnetos.

A magneto is a device that converts the mechanical energy received from

the engine into electrical energy, the electricity thus produced being

used to ignite the charge in the engine. This appliance does away with

all of the troubles incident to a rapidly deteriorating chemical battery

and produces a much hotter and uniform spark. A magneto is especially

desirable with multiple cylinder engines where the demand for current is

almost continuous, as the amount of current delivered by the magneto has

no effect on its life or upon the quality of the spark.

The principal parts of the generating system of the magneto are the

magnets, the armature, the armature winding, and the current collecting

device, of which the armature and its windings are the rotating parts.

The production of current in the magneto is the result of moving or

rotating the armature coil in the magnetic field of force of the

magnets. When any conductor is moved in a space that is under the

influence of a magnet a current is generated in the conductor which

flows in a direction perpendicular to the direction of motion. The value

of the current thus generated depends on the strength of the magnetic

field, the speed with which it is cut, and the number of conductors

cutting it that are connected in series. Roughly, the voltage is

doubled, with an increase of twice the former speed, and with all other

things equal, the voltage is doubled by doubling the number of

conductors connected in series.

By employing powerful magnets, and a large number of conductors (turns

of wire) on the armature it is possible to obtain sufficient voltage for

the ignition system at a comparatively low speed. The number of amperes

delivered depends principally upon the internal resistance of the

armature and the external circuit, and not on the number of conductors,

nor directly upon the strength of the field. For this reason, low

voltage machines that are intended to deliver a great amperage have only

a few conductors of large cross section, while high tension machines

have a great number of conductors of small size. In all cases the

magneto, or ignition dynamo must be considered simply as a generator of

current in the same way that a battery is a source of current since the

current generated by them is utilized in precisely the same way.

The class of ignition system on which the magneto is used determines the

class of the magneto. The low tension magneto is used principally for

the make and break system, although it is sometimes used in connection

with a high tension spark coil or transformed in the same way that a

battery is used with a vibrator coil. The high tension magneto is used

exclusively with the jump spark system and high tension spark plug.

These classes are again subdivided into the direct and alternating

current divisions, depending on the character of the current furnished

by the magneto. Briefly a continuous current is one that flows

continually in one direction while an alternating current periodically

reverses its direction of flow. As the alternating current magneto is

the most commonly used type, we will confine our description to this

class of magneto. The alternating current magneto is much the simplest

form of machine as it has no commutator, complicated armature winding,

nor field magnet coils, and in some types the brushes and revolving wire

are eliminated.

As the magnetic flux of an alternating magneto is changed in value, that

is increased and decreased, twice per revolution, it follows that the

current changes its direction twice for every revolution of the

armature. Each change in the direction of current flow is called an

alternation.

The voltage developed in each alternation or period of flow is not

uniform, the voltage being low at the start of the alternation, rapidly

increasing in voltage until it is a maximum at the middle, and then

rapidly decreasing to zero, from which point the current reverses in

direction. As we have two such alternations, in a shuttle type magneto,

per revolution we have two points at which the maximum voltage occurs;

that is in the center of each alternation. These high voltage points are

called the peak of the wave and consequently the sparking devices should

operate at the peak of the wave or at the point of highest voltage. The

spark therefore should occur when the shuttle or inductors are at a

certain fixed point in the revolution at which point the peak of the

wave occurs. The peak of the wave occurs when the shuttle is being

pulled or turned away from the magnets.

In what is known as the “shuttle type” alternating current magneto, the

generating coil is wound in the opening of an “H” type armature. This

iron armature core is fastened rigidly to the driving shaft and revolves

with it. As the armature revolves, it is necessary to collect the

current that is generated by means of a brush that slides on a contact

button B, the button being connected to one end of the winding.

(98) Low Tension Magneto.

The winding of the low tension magneto consists of a few turns of very

heavy wire or copper strip, one end of which is grounded to the armature

shaft and the other passing through the hollow shaft from which it is

insulated. The end of the insulated wire is connected to the contact

button (B) on which the current collecting brush presses. As one end of

the winding is grounded, one brush, and one connecting wire is saved as

the current returns to the magneto through the frame of the magneto. As

the shuttle revolves between the magnet poles the magnetism is caused to

alternate through the iron of the armature, thus causing the current to

alternate in direction and fluctuate in value.

Since there are only two points at which the maximum current can be

collected during a revolution with the alternating current magneto, it

is necessary to drive it positively through gears, or a direct

connection to the shaft so that this maximum point of voltage will

always occur at the same point in regard to the piston position. If it

is driven by belt without regard to the position of the piston, it is

likely that there will be many times that the voltage is zero or too low

in value when the spark is required in the cylinder. Alternating current

magnetos must be positively driven, and the armature must be connected

to the engine so that the peak of the wave occurs at, or a little before

the end of the compression stroke.

With this type of magneto the only point that is likely to give trouble

is the point at which the brush makes contact with the contact button.

If the brush should stick or not make contact, or if the button is dirty

or rusty, the current will not flow; this point should always be given

attention. Outside of this the only attention necessary is to keep the

bearings oiled.

[Illustration:

Fig. 101. Sumter Magneto Advanced.

]

[Illustration:

Fig. 102. Sumter Magneto Retarded.

]

[Illustration:

Fig. 103. Sumter Magneto on Horizontal Engine.

]

Fig. 101 and Fig. 102 show the Sumter low tension magneto as arranged

for make and break ignition. The armature and its connections are of

exactly the same type as that shown in the previous diagram. The magnets

and frame are arranged to tilt back and forth so that the peak of the

wave will occur at the advanced and retarded positions of the igniter.

This arrangement allows the full voltage of the magneto to be obtained

at any point within the range of the ignitor, an important item when

starting the engine or running at low speed. When mounted on the engine,

as shown by Fig. 103, the magnets are provided with an operating rod

that is marked “start” and “run.” When the pin on the engine bed is

engaged under “start,” the magneto is retarded, when the pin is under

“run” it is advanced. A number of intermediate points are provided at

which the operating arm is held fast by tooth engagements as shown in

the slotted handle. As shown in the illustration the magneto is fully

advanced. The gears by which the magneto is driven are clearly shown in

the cut, the ratio between the gear on the crank shaft and that on the

magneto shaft being exactly 2 to 1. One lead is carried to the make and

break igniter in the cylinder head, the current being returned through

the bed of the engine. The same make of magneto is shown mounted on a

vertical engine in Fig. 104. In this case the magneto is positively

driven from the crank shaft of the engine by a chain. The single

conductor running from the magneto to the cylinder heads is clearly

shown. To start the engine, the igniter is set in the usual manner and

the magneto tilted to starting position, as shown in the illustration.

The engine is then started in the usual manner and, when running, the

igniter is changed to running position, and the magneto is tilted

outwardly. It is not important which is changed first, the magneto or

the igniter. It is easy to remember the “starting” and running

“position” of the magneto, the running position always being that in

which the magnetos are tilted in the direction opposite to that in which

the engine runs.

(99) Care of Low Tension Magnetos.

(1) Avoid setting a magneto on an iron or steel plate, unless stated

otherwise in the manufacturer’s directions, as in some makes the

magnetism will be short circuit by iron or steel and will reduce the

output.

(2) Do not jar magnets or magneto unnecessarily, for this tends to

weaken the magnets.

(3) Never remove the magnets if it can possibly be avoided. If this must

be done, mark the magnets and gears so that they may be replaced in

exactly the same position. If your magneto refuses to generate after

reassembling it is probable that they are reversed in position or that

the magnetism has been knocked out of them while off of the magneto.

(4) As soon as the magnets are removed, or better before, place a plate

of iron or steel across both ends of the magnet. Don’t leave the magnets

without this keeper for any length of time or they will lose their

magnetism. The best plan is to leave the magnets alone.

(5) Remember that the running clearance between the magnets and armature

is very small, only a few thousandths of an inch, and that any error in

replacing the bearings in their proper position will cause the armature

to bind in the tunnel. Handle armature carefully and do not lay it in a

dirty place as a bent shaft or grit in the armature tunnel will fix it

permanently.

(6) Most all magnetos are practically water proof, but don’t experiment

with the hose.

(7) Make all connections firmly and have the wire clean under the

binding posts.

(8) Only a few drops of oil are needed at long intervals, don’t neglect

to oil them, but above all do not drown them with oil.

(9) Examine the brush occasionally and clean off all oil and dirt.

(10) When replacing the magneto on the engine after its removal see that

the gears are meshed in the former position. Best to mark the teeth

before removal.

(100) High Tension Magnetos.

The “true” high tension type magneto is complete in itself, requiring no

jump spark coil nor timer, the high tension current being generated

directly in the coils carried by the armature. This arrangement reduces

the wiring problem to a minimum, as the only wires required are those

leading directly to the spark plugs, and one low tension wire connecting

the cutout switch used for stopping the engine.

[Illustration:

Fig. 105. Single Cylinder High Tension Bosch Magneto.

]

The armature of this type of magneto carries two independent windings,

one of a few turns of coarse wire called the primary coil, and the other

consisting of thousands of turns of extremely fine wire called the

secondary coil. It is in the latter coil that the high tension current

is generated. The timer is connected directly to the armature shaft, and

is an integral part of the magneto. All primary connections are

therefore made within the magneto.

Belts or friction drives cannot be used with this type of magneto.

As there are no vibrators or independent coils used, the spark occurs

exactly at the instant that the timer operates or breaks the primary

circuit. It will be noted that the spark is produced with this magneto

when the primary circuit is broken by the timer, instead of made as is

the case with battery coils, or coils used with low tension magnetos.

There is no lag and consequently the time of ignition is not affected by

variations in the engine speed, which requires an advance and retard of

the spark with batteries and vibrator coils.

When used with multiple cylinder engines the high tension magneto is

provided with a distributor, which connects the high tension current

with the different cylinders in their proper firing order. The timer

determines the time at which the spark is to occur and the distributor

determines the cylinder in which the spark is to take place.

[Illustration:

Fig. 106. Connecticut High Tension Magneto.

]

The sparks delivered by the high tension magneto are true flames or arcs

of intense heat, and exist in the spark gap for an appreciable length of

time. It is evident that such flames possess a much greater igniting

value than instantaneous static spark delivered by the high tension

spark coil used with the battery or operated by the low tension magneto,

and are capable of firing much weaker mixtures.

Like low tension magnetos, the true high tension type may be of either

the inductor or shuttle wound class. All high tension magnetos are

positively connected or geared to the engine in such a manner that there

is a fixed relation between time of the current impulse produced by the

magneto and the firing position of the engine piston.

The current is generated on the same principle as in the low tension

shuttle type; that is, by a coil of wire revolving in the magnetic field

established by permanent magnets.

During each revolution of the armature, two sparks are produced at an

angle of 180° from each other.

The advance and retard of the spark is obtained by means of the timing

lever which shifts the timer housing back and forth which results in the

primary current being interrupted earlier or later in the revolution of

the armature.

[Illustration:

Fig. 107. Longitudinal Section Through Bosch High Tension Magneto.

]

The timing lever can turn through an angle of 40° measured on the

armature spindle, and the angle of advance for multiple engines is as

follows:

Advance for 1 cylinder 40°

Advance for 2 cylinders 40°

Advance for 3 cylinders 50°

Advance for 4 cylinders 40°

Advance for 6 cylinders 27°

A timer is used with the magneto on a “jump spark” system in the same

way as with a battery, providing a vibrating coil is used.

In one type of magneto the Connecticut, the coil is part of the magneto,

and is fastened to the magneto frame. This type of magneto uses a

non-vibrating coil, and produces but a single spark each time the

primary circuit is broken by the magneto timer. As the timer on this

type is driven by the magneto shaft, it is evident that the magneto must

be “timed” with the engine, or must have its armature shaft connected to

the shaft of the engine in such a manner that the timer contact is

broken, and the single spark produced at the instant that ignition is

required in the cylinder.

Unlike the dynamo, the alternating current magneto cannot be used with a

storage battery, the alternating current producing no chemical change in

the electrodes of the battery.

[Illustration:

Four Cylinder “D4” High Tension Bosch Magneto Showing Distributor.

]

The Bosch high tension magneto is a typical high tension magneto having

the primary and secondary windings wound directly on the armature shaft,

there being no external secondary coil. The end of the primary winding

is connected to the plate (1) Fig. 107, which conducts the current to

the platinum screw of the circuit breaker (3). Parts (2) and (3) are

insulated from the breaker disc (4), which is in electrical contact with

the armature core and frame. When the circuit breaker contacts are

together the primary winding is short circuited, and when they are

separated the current is broken and the spark occurs. The breaker

contacts are simply two platinum pointed levers that are separated and

brought together by the action of a cam as they revolve. A condenser (8)

is provided for the circuit breaker to suppress the spark and to

increase the rapidity of the “break.”

The secondary winding of fine wire is a continuation of the primary

winding, and the secondary is wound directly over the primary. The outer

end of the secondary connects with the slip ring (9) on which slides the

carbon brush (10), which conducts the high tension current from the

armature. This brush is insulated from the frame by the insulation (11).

From (10) the current is led through the bridge (12) through the carbon

brush (13) to the distributor brush (15). Metal segments are imbedded in

the distributor (16), the number of which corresponds to the number of

cylinders. As the brush rotates, it makes consecutive contact with each

of the segments in turn and therefore leads the current to the cylinders

in their firing order. Wires from the cylinders are connected to sockets

that in turn connect with the segments. The disc driving the distributor

brush (15) is geared from the armature shaft in such a way that the

armature turns twice for every revolution of the distributor, when four

cylinders are fired, and three times for the distributors once when six

cylinders are fired.

[Illustration:

Fig. 108. Bosch High Tension Circuit.

]

The voltage of the current generated in the secondary coil by the

rotation of the armature is increased by the interruption of the primary

circuit caused by the opening of the contact breaker.

At the instant of interruption of the primary circuit the high tension

spark is produced at the spark plug.

As the spark must occur in the cylinder of the engine at a certain

position of the piston, it is necessary that the interrupter act at a

point corresponding to a definite position of the piston, consequently

this type of magneto must be driven positively from the motor by means

of gears, or directly from the shaft.

These magnetos run in only one direction. This running direction should

be given when magneto is ordered, as being “clockwise” or

“counter-clockwise” when looking at the driving end of the magneto.

The magneto for the single and double cylinder engines has no

distributor, the high tension current being led directly from the

armature.

The circuit diagram of the Bosch four cylinder magneto is shown by Fig.

108, the winding and plug connections being clearly shown. When

connecting the magneto care should be taken to have the distributor and

plug connections arranged so that the cylinders will fire in the proper

order.

(101) Bosch Oscillating High Tension Magneto.

The oscillating type of magneto is used on slow speed heavy duty engines

that move too slowly for the ordinary type of magneto. In the

oscillating type the armature is given a short angular swing by the

action of a tripping device operated by the engine which results in an

intense spark at the lowest speeds.

Magneto type “29” is constructed with two powerful steel magnets, while

magneto type “30” is provided with three; an armature of the shuttle

type is arranged to oscillate between their pole-shoes.

The magneto is actuated by a rotating cam or other suitable device,

which moves the armature 30° from its normal position whenever ignition

is required. To permit this movement, a trip lever is mounted upon the

tapered end of the armature shaft, this trip lever being held in a

definite position by the tension of the spring or springs 1. The trip

lever is only supplied when specially ordered, but each magneto is

provided with the necessary springs and spring bolts.

When the trip lever is moved from its normal position by the operating

mechanism, the springs are extended, and when the operating mechanism

releases the trip lever, the later returns the trip lever and armature

to their normal position, this movement resulting in the production of a

sparking current in the armature winding.

The winding of the armature is composed of two parts, one being the

primary winding, which consists of a few turns of heavy wire, and the

other the secondary winding, which consists of many turns of fine wire.

The tension of the current produced by the oscillation of the armature

is increased by closing the primary circuit at a certain position in its

movement, and then interrupting it by means of the breaker. At the

moment of the interruption, an arc-like spark is formed at the spark

plug and ignition occurs.

[Illustration:

Fig. 109. Elevation of Bosch Oscillating Magneto for Slow Speed

Engines. High Tension Type.

]

On cam shaft (c) two cams are mounted side by side. One of these cams

(a) is to be used for starting the motor, or for the retarded spark

position, while the second (b) is to be used for operation, or for the

full advance position. These cams are mounted on a sleeve, which may be

moved longitudinally on the shaft, so that the trip lever may be

operated by cam (a) or cam (b) as desired. The sleeve is caused to

rotate with the shaft by a key. Between the cam (b) and a fixed collar

(f) a spiral spring is arranged, which tends to maintain the sleeves in

the position when the cam (b) is in operation. A stop collar is also

provided to limit the movement of the sleeve beyond this full advance

position. Over this collar is fitted a hand wheel, which, in the

position illustrated in the diagram, acts together with the collar as a

stop. Around the collar is a circular key-way, and a brass bolt is

located in the hand wheel to lock into this key-way when the hand wheel

is pushed into the position indicated by the dotted lines. This movement

of the wheel forces the cam sleeve forward, and brings the retarded cam

(a) into the operating position to permit the engine to be started.

(102) The Mea High Tension Magneto.

[Illustration:

Fig. 110. Diagram of Oscillating Magneto, Showing Cam and Trigger

Arrangement.

]

The low tension winding of the ordinary type of magneto is

short-circuited by a breaker which opens at certain points of each

revolution with the result that a high voltage is generated across the

high tension winding at the moment of the break, and a spark produced

across the spark gap in the cylinder to which it is connected. The

quality of this spark, or in other words the heat value, depends among

other factors upon the particular position of the armature in relation

to the magnetic field at the moment the spark is produced. As the

armature in this type of magneto is in a favorable position for

obtaining a spark twice every revolution, two sparks can be obtained per

revolution. The timing of the spark is accomplished by opening the

breaker earlier or later, by shifting the breaker housing naturally with

the unavoidable result that if the position of the magnetic field

remains stationary, the relative position between armature and field at

the moment of the break must vary. Since, however, as explained above,

the quality of the spark depends upon this relative position, it is

apparent that a good spark, can, with a stationary magnetic field, be

produced only at one particular timing.

[Illustration:

Fig. 111. Side Elevation of “Mea” Magneto, Showing the Magnets, and

Cradle in Which the Magneto Swings When Advanced and Retarded.

]

[Illustration:

Fig. 112. Longitudinal Section of “Mea” High Tension Magneto.

]

The result of these conditions are known to everybody familiar with

automobiles. They are the difficulty of cranking a motor on one of the

average high tension magnetos, if the spark is fully retarded, and of

operating the motor on the magneto at very low speed, particularly when

it is overloaded, as for example, in hill climbing. Attempts have

therefore been made to obtain the spark, independent of the timing,

always at the same favorable position of the armature.

The distinct innovation and improvement incorporated in the Mea magneto

consists in bell shaped magnets (Fig. 111) placed horizontally and in

the same axis with the armature, instead of the customary horse-shoe

magnets placed at right angle to the armature.

This at once makes possible and practicable the simultaneous advance and

retard of magnets and breaker instead of the advance and retard of the

breaker alone as the magnets may be moved to and fro with the breaker

housing. It will be seen that as a result of this new departure the

relative position of armature and field at the moment of sparking is

absolutely maintained, and the same quality of spark is therefore

produced, no matter what the timing may be. Furthermore, the range of

timing, which with the horse-shoe type of magneto is limited to 10° or

15° at low speeds (i. e. at speeds at which a retarded spark is of

value) becomes limited only by the necessity of supplying a suitable

support for the magnets. With the standard types of Mea magnetos

described in the following, this range varies from about 45° to 70°, but

if necessary this range can be increased to any amount desired.

The bell-shaped magnets are fixed to the casing which is mounted on a

base supplied with the magneto. The timing is altered by turning the

casing and magnets together on the base.

Fig. 112 shows a longitudinal section of a four cylinder Mea magneto.

The armature F with the ball bearings 17–18 rotates in the bell-shaped

magnets 100, the poles of the magnets being on a horizontal line

opposite the armature 1. The armature is of the ordinary H type iron

core wound with a double winding of heavy primary and fine secondary

wire. On the armature are mounted the condenser 12, the high tension

collector ring 4, and the low tension circuit breaker 26–39.

The circuit breaker consists of a disc 27 on which are mounted the short

platinum 33, the other contact point 34 is movable and is supported by a

spring 30 which is fastened to the insulated plate 28 mounted on disc

27. Fiber roller 31 in connection with cam disc 40 which is provided

with two cams is located inside the breaker. Revolving with the armature

the roller presses against the spring supported part of the breaker

whenever it rolls over the two cams which of course is twice per

revolution.

[Illustration:

Magneto of Roberts Motor in Advanced Position.

]

[Illustration:

112-a. Advance and Retard Mechanism Used in the Roberts Motors. The

Magneto is Driven by a Helical Gear from the Small Pinion. By

Shifting the Gear Back and Forth on the Pinion, the Armature of the

Magneto is Advanced or Retarded in Regard to the Piston Position.

The Reason for this Change Will be Seen from the Cuts by Noting the

Position of the Lower Helix.

]

Inspection of the breaker points is made easy by an opening in the side

of the breaker box. The box is closed by a cover 74 supporting at its

centre the carbon holder 47 by means of which the carbon 46 is pressed

against screw 24. This latter screw connects with one end of the low

tension winding while the other end is connected to the core of the

armature. It will, therefore, be seen that the breaker ordinarily

short-circuits the low tension winding and that this short-circuit is

broken only when the breaker opens; it will also be apparent that when

the screw 24 is grounded through terminal 50 and the low-tension switch

to which it is connected, the low-tension winding remains permanently

short-circuited, so that the magneto will not spark. The entire breaker

can be removed by loosening screw 24.

The high tension current is collected from collector ring 4 by means of

brush 77 and brush holder 76, which are supported by a removable cover

91 which also supports the low tension grounding brush 78 provided to

relieve the ball bearings of all current which might be injurious. Cover

91 also carries the safety gap 89 which protects the armature from

excessive voltages in case the magneto becomes disconnected from the

spark plugs.

The distributor consists of the stationary part 70 and the rotating part

60 which is driven from the armature shaft through steel and bronze

gears 7 and 72. The current reaches this distributor from carbon 77

through bridge 84 and carbon 69. It is conducted to brushes 68 placed at

right angles to each other and making contact alternately with four

contact plates embedded in part 70. These plates are connected to

contact holes in the top of the distributor, into which the terminals of

cables leading to the different cylinders are placed.

In the front plate of the magneto is provided a small window, behind

which appear numbers engraved on the distributor gear which correspond

to the number of the cylinder the magneto is firing. This indicator is

of great value as it allows a setting or resetting after taking out,

without the necessity of opening up the magneto to find out where the

distributor makes contact.

The magneto proper is mounted in the base 53 which is bolted to the

motor frame and the arrangement is such that the magneto can be removed

from its base by removing the top parts 60a and 60b of the two bearings.

The variation in timing is affected by turning the magneto proper in the

stationary base which is accomplished by the spark lever connections

attached to one of the side lugs 88. The spark is advanced by turning

the magneto opposite to rotation and is retarded by turning it with

rotation. One cylinder magnetos are similar to the four cylinder except

that the distributor and gears are omitted.

(103) The Wico High Tension Igniter.

Practical Hand Book of Gas, Oil and Steam Engines Stationary, Marine, Traction; Gas Burners, Oil Burners, Etc.; Farm, Traction, Automobile, Locomotive; A simple, practical and comprehensive book on the construction, operation and repair of all kinds of engines. Dealing with the various parts in detail and the various types of engines and also the use of different kinds of fuel. · 第 18 / 20 章

Batteries that are capable of being operated only for short periods, on