Starter woes

[adam912]

Hi All-

I've been driving a 66 Porsche 912 since the 70s. In around 2001 I converted to a 2.2 liter Type 4 motor. It's been a great source of fun!
3 years ago I parked the car, intending to do some head work on it and get the car back on the road, but got side tracked by rust worm repairs. With the engine rebuilt as of this Spring, I decided to spin up the motor before I reinstalled it, so I bolted engine and transmission together on my garage floor.

When I applied battery power to the starter, I got this horrible clacking sound, much like the sound of an impact wrench. It does turn the engine over, but this noise sounds like destruction in action. I've tried to attach an MP4 or WAV file, but this board doesn't seem to want to accept either type.
I've torn the starter and solenoid apart, cleaned everything thoroughly, gotten the solenoid contactor pieces and the commutator nice and shiny, but no joy.
I've made sure the battery was charged, and even tried to supply power from my wife's Volvo. Made no difference.

Anyone got an idea of what's gone south here? The starter is at least 20 years old, but it never let me down previously, and it looked pretty clean inside.
The starter is a vanilla Bosch SR-17.
Any ideas much appreciated!
cheers
Adam912. Out.

[Bahman]

MY want to remove the starter and plugs and manually spin the engine. If the noise still present, the problem may be caused by the top end engine work. If the noise is not present, I’d get a new/ hood used starter.

[ejboyd5]

Does the drive gear on the starter extend enough to make full contact with the gear teeth on the flywheel?

[adam912]

Starter on the bench seems to extend the pinion plenty. The spec is around 0.400 inch, and my calibrated eyeball says it's in the ballpark.
One thing I noticed--while I had the starter out, I powered it up and held the starter so that I could press the spinning pinion gear down on a piece of wood.
I was able to push the pinion gear in pretty easily. Shouldn't the solenoid be pushing the bendix and pinion gear a little harder than this?
I never tried this with a working starter, just wondering?

[adam912]

BTW, this is all with plugs out. I verified that the motor turns nice and easy when rotated by hand.

[Theunz]

If you replaced the flywheel it might not have the proper number of teeth. I don’t know if this is possible on the 911 engine but it is on other engines.

[adam912]

No flywheel replacement, nothing but reinstalling parts that sat for a few years. I think I got to the root cause, though:
I removed the solenoid, then used vise grips to hold the Bendix actuating rod so the pinion gear stayed extended.
Reinstalled the starter, hit the juice. Starter goes like a rocket! Engine spins as it should.
I suspect that the solenoid had been marginal for some time, and perhaps moisture got into it.
At any rate, a new solenoid is on the way, and I'll report in when I have it installed and tested.
Thanks to all for the great suggestions!
Adam912.Out.