TRACTOR ARRANGEMENT
The uneven ground over which tractors must work requires the weight to
be kept low, to prevent capsizing, and they are also built wide, for
the narrower they are the more easily they tip over. They cannot be
broad in front, however, for if they are the steering wheels cannot
be swung enough to permit them to turn in the small circle that is
desirable.
To give a small turning circle some tractors are built with the front
of the frame raised enough to permit the wheels to cut under. Others
use small steering wheels, but this is not desirable because small
wheels will not run over rough ground as readily as large ones, and
steering is difficult.
[Illustration]
[Illustration: FIG. 68.—TRACTOR ARRANGEMENT]
[Illustration]
[Illustration: FIG. 69.—TRACTOR ARRANGEMENT]
Types of tractors are indicated in Figures 68 and 69. A has a
4-cylinder vertical engine in front, driving both wheels by bull gears,
while B is a 2-cylinder horizontal engine in the center, driving both
wheels by chains. C has a 4-cylinder vertical engine set across the
frame. These three types have riveted steel frames, to which the parts
are attached.
In D, the drive is entirely enclosed within the rear axle housing,
and the rear part of the frame is formed by the axle housing and the
housing of the change speed gear.
E has a 1-cylinder horizontal engine with a single chain drive, while F
has a similar engine but drives to both wheels.
G has no frame, its place being taken by the crank case of the engine
and the housings of the parts of the transmission. G and H have
4-cylinder vertical engines, G driving through an enclosed rear axle
and H through bull gears.
[Illustration: FIG. 70.—“GRAY” TRACTOR]
Figure 70 has one broad wheel instead of two narrower ones, this being
placed inside of the frame instead of outside. It has a 4-cylinder
vertical engine placed across the frame, and drives through two chains.
[Illustration]
[Illustration: FIG. 71.—TYPES OF FRONT AXLES]
The front axle of a tractor is almost always attached to the frame by
a pivot, so that the wheels will follow uneven ground. Some of the
forms of front axles are shown in Figure 71.
[Illustration: FIG. 72.—SPRING SUPPORT]
The first is a plain bar, while the second is arched to raise the front
of the frame in order to permit the steering wheels to cut under. In
the third the wheel axles are mounted on springs, which take up some of
the vibration and act as shock absorbers.
The fourth axle shown is built of steel bars riveted together to form
a truss, and the fifth is similar, with the frame pivot carried on
springs. The sketches at the bottom indicate the extent to which the
pivoted front axle may swing.
Figure 72 shows a spring support for the axles, front and rear.
The axle bearing is in a block sliding in guides, the weight being
supported by a heavy spring.