How to troubleshoot inop starter?

[Formerly Steve Wilkinson]

Car is an '83 911SC with a year-old Tilton lightweight starter. Suddenly stopped starting yesterday. Battery is a known-good Optima two years old, indicates a "resting pulse" of 13 volts on a multimeter.

Whether or not the alternator is working correctly is irrelevant right now, since I have a new one on the way.

I originally thought the alternator was the problem, since I was able to restart the car by jumping it the first time the starter didn't work. After that one successful restart, however, jumping has no effect, either from a charged-up Kwikstart or from a running car. (One other odd symptom that may have nothing to do with anything, or may be a key to...well, to something: about five minutes after restarting the car with a jump, it went through a single three-second period of very harsh cutting on and off while I was accelerating. Car has carburetors (PMOs) but this was nothing like a fuel fault, it felt as though the ignition (twin MSDs, twin plugs) was shutting on and off.)

All I'm getting is a click from the solenoid--not a clatter or whirr, just a single click per key turn.

I tried jumping the ignition-wire tab to the starter-winding cable, still just a click, which leads me to believe the ignition switch is good andt he wiring form the switch to the starter is good.

Then I tried jumping directly from the battery cable to the starter-winding cable. Nothing. Shouldn't this make the starter crank, and does that mean the starter motor and not the solenoid is the problem?

[911pcars]

Stephan,
You performed all the inspections I would do. It looks like the starter motor isn't right.

It could be something with the brushes as they provide ingress and egress for current flow through the motor... or a short or open in the armature or field coils. Anyway, it sounds internal rather than anything in the vehicle electrical system.

Bypassing the solenoid as you did should have caused the motor to rotate.

Next step is to remove and bench-test. These are costly enough to motivate me to dissect the starter and see if it's a candidate for a DIY repair. Worst case - take the motor to a rebuilder and have it rewound/repaired.

Sherwood