Starter motors

We started off by our normal safety procedure, overalls etc.
we needed our tools, mainly screwdrivers and sockets, then we got started.

We were given a starter motor and was told to find a problem (later revealed it had no problem, but to teach us how to find out it didnt).it was tested on a test bench where the operator made it look like it had a problem so then we could investigate.

We started by taking the starter completly apart so then we could test and examine all the individual parts.
from solenoid to commemtator and brush plate, etc.
to disassemble we removed the M terminal wire from the solenoid, removed screws from the commutator housing, removed the commutator housing, removed the brushes aswell as the brush plate, removed the armature, etc.

First was the visual inspection on the armature, there was no overheating, no burning, no physical damage and a little it of poling...by little i mean tiny suface scratches.

next test was ground testing the windings with a multi meter, the reading must read (infinity) as there is no circuit between the winding and the ground, if there is a connection to earth, the winding needs to be replaced or re-wound.

next test, continuity circuit test.
using the multi meter set to ohms, check each commutator segment with 1 probe on 1 segment and dragging the other probe around the rest of the segments. test result was 0.0001Ohms - serviceable.

next test, measuring commutator diameter.
taking a vernier caliper to measure, we measured the diameter of the commutator, result: 31mm.
26.8-31mm being the manufacturer'a specs.

next test, the growler test
placing the armature onto the growler machine and rotating the armature 360degrees whilst lightly balancing  a hacksaw blade upon the top. If the hacksaw blade starts to chatter along the armature during rotation on the growler, there is a short circuit along the armature segments. Result: no chatter-serviceable

next the brushes were examined.
The brushes was measured and were at a serviceable length.
a quick visual examination shows they were also in good condition.

next the solenoid magnetic switch was tested.
Terminals: B-battery power, S-ignition/starter switch supply and M-Starter motor supply.
A 9V power supply was hooked up to its terminals, it drew a current of 25Amps and the solenoid plunger pulled in...operated as it should.

after a long session of testing, i come to the last test of the starter, checking the pinion gear and clutch.
the pinion gear has little to no wear and tear, the bushes are in good condition and has little "play" and the one-way clutch operates as it should.

Q and A

1.To turn the engine enabling it to start.

2. 1-Armature
    2-Field coils and pole shoes
    3-Housing
    4-Brushes
    5-Bushes
    6-starter drive

3.clockwise

4. 1-inertia
    2-pre-engaged
    3-gear-reduction

5.

6. Front view of a starter motor clutch.

 

7. The pinion is turning in direction of the arrow 

at a speed higher than it should go when the engine has started.

the clutch allows it co compensate briefly and safely pull away.

8. Series wound starter internal circuit.

9. Designed for low compression motors, produces high torque on low revs and low torque on high revs (vice versa).

10.