ElMariachi

Thanks for the ideas. I'll tear it apart this winter and figure out what's going on.

I finished the modification and it's a success, pictures attached. There is definitely something screwy with the flywheel/bell housing configuration. As I was installing it I pulled the spark plugs and rotated the crank shaft to listen for interference. I heard a little scraping and I painted part of the motor housing. There is about 3mm where the ring gear was grinding on the enclosure. I suspect the engine and transmission are not stock for a '76 since it has a four speed transmission and the block/head stamps match those of a '77. Regardless, I'm happy it's working again, thanks for everyone's input.

I am constrained to working on it part time on some weekends, real life gets on the way. I tried a couple different starters and they all have the exact same dimensions, including one with gear reduction. So, this is not going to be solved easily by replacing the starter. I think the long term fix is to drop the transmission and replace the ring gear and possibly the flywheel (and definitely the clutch while I'm in there). In the short term, I'm modifying one of the extra starter motors with a custom made bracket that would mount the starter and ~8mm deeper into the bell housing. This means cutting off the cast aluminum mounting tabs and attaching my bracket in the same orientation but recessed from the original. It's going to be super ugly but a chance to practice welds. I'll post pictures if I have any success.

Pictures of the ring gear and old starter motor pinion attached. There is some wear on the ring gear but just on the tooth tips. The starter had hardly and wear. I did some measurements. From the outside of the bell housing cover plate to the nearest edge of the ring gear is about 18mm. On the starter motor the pinion gear starts at about 8mm from the cover plate interface so the gear has about 10mm travel before it could begin to interface with the ring gear. The pinion gear appears to have 13 mm travel leaving only 3mm to of gear teeth mesh. Since the pinion gear is rounded and the ring gear front tooth edge is worn there is probably little to no contact between the gear tooth faces. Can anyone recommend a starter motor that is ~8mm longer or a source for drawings of motors that I could search through?

It's worked great for the last year since I bought it. I've been doing a lot of work on it and have been using it a lot more now that it's running well.

I just replaced the starter motor in my '76 280z. The original symptom was that the starter would spin fast but not engage the flywheel. The ring gear has some wear on the teeth edges but no broken teeth. The new starter does the same. I pulled the plugs and put a hand switch on the solenoid. When I trigger the solenoid the motor will turn the engine a little bit and then the starter motor will spin but not rotate the crankshaft. Any help would be greatly appreciated. Thanks.