YOUR BEARINGS
Ever stop to count up how many bearings there are about your car? If
you haven’t, you are likely to lose your bearings while you hunt for
the several hundred bearing points of the modern automobile.
A bearing is a support for a moving member, so designed as to minimize
friction and receive wear, and to permit of fine adjustment.
There are many types of bearings, some in which the metals are selected
with the idea of obtaining strength rather than non-friction qualities;
others have strong metal shells lined with a comparatively soft
non-friction metal. In these bearings moving members slide over each
other.
In addition to this we have the so-called anti-friction bearings, in
which balls, or straight, taper, or helical rollers are used, giving a
rolling rather than a sliding contact.
On the engine alone there are 102 bearings. This is figured on the
average six-cylinder motor; some of them have more than double the
number. There are, for instance, the following:
Six cylinders, 6 wrist-pin bearings, 6 crank-pin bearings, 4 main, 3
cam shaft, 12 cam, 12 push rod, 12 valve stem, 2 fan, 2 water pump, 8
ignition, 6 spark control, 6 carburetor control, 6 carburetor, 3 oil
pump, 4 self-starter, and 4 self-starter linkage bearings; total, 102.
The first named, cylinder and piston, not generally termed bearings,
are usually of cast iron, which gives comparatively long wear and in
which the friction is not great if well lubricated. When wear does
occur at this point it is necessary to rebore and have larger pistons
fitted.
The wrist-pin bearings usually are in the form of a bronze shell,
called a bushing, surrounding the wrist pin; when wear occurs it is
necessary to drive out the bushing and replace with a new one which
fits.
The crank-pin bearings are usually in halves, the metal babbitt or
bronze, surrounded by a steel strap or casing. When wear occurs,
the adjustment is made by taking out thin sheets of metal, called
shims, which allow the halves to be brought closer together. The main
crank-shaft bearings are of the same type.
The cam-shaft bearings are usually in bushing form, which must be
replaced with new ones when they become worn. The cam-follower bearings
may be just flat plates resting directly upon the cam, or rollers
running on a pin in the valve push rod. Wear in these parts would
usually be compensated for by adjusting screws on the valve push rods.
The push-rod guides are sometimes made of cast iron or other metal,
with babbitt or bronze shell in bushing form, and would require
replacement when worn.
The oil-pump bearings consist of a plunger working in a small cylinder,
with one end bearing against a cam, or a pair of gears driven from the
cam shaft. These bearings, being perfectly lubricated, seldom or never
require adjustment.
All of the bearings considered so far are cared for by the lubricating
system of the engine, which starts when the engine starts to run, and
as long as oil is kept in the engine they are quite certain to be taken
care of, barring accidental stoppage of the oil lead.
The fan usually runs on ball bearings which are lubricated with a
squirt can; being usually of the cup and cone type, they are adjusted
by tightening the cone. The water-pump bearings are lubricated by
compression grease cups; when the bearings become badly worn it is
necessary to drive out the bushings and replace them; generally the
shaft also will need replacing. When this shaft becomes worn out of
round, no amount of tightening of the stuffing box will prevent water
from leaking out.
The valve-stem guides are sometimes bushings, but more usually are
holes bored through the cylinder casting. In the former case, when
wear occurs the bushing may be driven out and a new one, with new
valve, installed; in the latter case, the holes must be reamed true and
larger, and valves with larger stems be inserted.
In the ignition system ball bearings usually are employed, with or
without means of adjustment. These are lubricated with an oil can or
packed in grease. There is one bearing of the ignition system which is
unique in that some manufacturers advise keeping it free of lubricating
substance of any kind. This is the rocker arm of the interrupter
on certain makes of magnetos. Other forms of interrupters are so
constructed that lubrication is advisable.
The carburetor air-valve bearing operates better if not lubricated,
but does wear and need replacing at times. The throttle bearings may
be lubricated and would certainly wear longer if this were done. When
they do wear air is admitted which is noticeable at low engine speed,
causing skipping and irregular running. Then the holes in the casting
must be enlarged and larger shaft inserted.
The throttle and spark-control linkage have a number of bearings, which
may be of the steel ball and socket type, or a wire bent to fit in an
eye. These pins should be frequently lubricated with a squirt can.
Usually they are not adjustable, so that parts must be replaced when
they become badly worn.
The self-starter motor and generator are usually equipped with ball
bearings and are lubricated with a squirt can. Both the motor and
generator have a copper commutator on which carbon brushes bear. These
are not bearings, strictly speaking, but they do require a very slight
trace of oil if the brushes have not been soaked in oil. The commutator
becomes worn occasionally and must be smoothed up with fine sand paper,
or, if badly worn, must be removed and trued in a lathe.
The other principal bearings throughout the car are usually of
ball or roller type, which may or may not be adjustable. Usually
the directions for the care and replacement are given in the
manufacturer’s instruction book.
In the steering gear there is a plain bronze bearing or bushing in
which the shaft is set out of center, so that when wear occurs by
twisting the bushing, the sector of the steering gear may be thrown
deeper into mesh with the worm and take up the play.
In the transmission gear, in which all other bearings are of the
ball or roller type, there will be found often a plain bearing on
the forward end of the square or fluted shaft called the pilot-shaft
bearing. This is one weak point in many otherwise satisfactory
transmissions. When this bearing wears, the operation becomes noisy
and the gears are difficult to shift. The transmission must be
disassembled, the bushing withdrawn and a new one pressed in.
The steering-gear linkage bearings are usually of the ball and socket
type, self-adjusting by means of springs. Steering knuckle bearings are
usually bushings which may be driven out and replaced when wear occurs.
It usually is necessary to replace the pins at the same time.
The universal joints of the propeller shaft become very noisy when
the bearings are worn. In modern construction these bearings are in
the form of bushings which may be replaced at small expense. The
brake linkage has many bearings, which are clevis and pin. These are
non-adjustable, and unfortunately are not often lubricated. When wear
occurs the holes may be drilled larger and larger pins be inserted, or
the parts may be replaced entirely.
Of course there are scores of other bearings in other parts of
the chassis, that with ordinary care last the life of the car.
The lubrication and adjustment are usually given in detail in the
manufacturer’s book of instructions and need no special caution other
than to advise following what is there printed.