Lesson 2
The Autolite starting motor, model MCZ 4005UT, is a typical
starter motor in use today on military vehicles. It is a sealed type (waterproof) starter and is used
on the 1/4-ton truck M151.
The motor operates on 24 volts and is a four-pole, four-brush unit. It is designed for underwater
operation but is not completely waterproof unless it is used with a waterproof flywheel housing. A
gasket is used to seal the starter to the flywheel housing. The starter is mounted on two flywheel
housing studs and held in place by two nuts and two lock washers.
Three bushing-type bearings which require no lubrication are used to support the armature shaft.
There is one bearing in each end plate, and one in the flywheel housing of the engine. The starter
drive is the Bendix Folo-Thru type.
The end play of the armature shaft is held within allowable limits by the use of thrust washers of
various thicknesses. The pole pieces (soft iron shoes) are attached to the starter frame by
countersunk screws. The field winding or coils are positioned around two of the pole pieces,
opposite to each other. This gives a four-pole action with only two field windings. The internal
resistance is kept low because there are only two windings.
When the starter switch is closed, current is passed through the two grounded brushes to the
commutator, which is located on the armature shaft. The armature has a number of heavy wires
wound around it in such a manner as to produce a magnetic field. After flowing through the
armature windings, the current is directed through two insulated brushes to the two field windings
and the pole pieces become magnetized. The magnetic fields of the pole pieces oppose the
magnetic field of the armature, causing the armature to rotate. The direction of rotation is
counterclockwise as viewed from the drive end of the starter. This direction of rotation is opposite
to that of most starters, but this starter is mounted over the transmission instead of being mounted
on the engine.
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