I just picked up a '73 ford 3550 that wouldn't start. Got her home and pulled the starter and found she had a relatively new starter and a slightly (?) chewed up gear ring. I know the usual advice is to split her and replace the gear ring, but I'm thinking this one is not that bad.
Full disclosure: the only time I've ever repaired a gear ring is when I threw out the flywheel in my M551 Sheridan tank, which coincidentally was also a '70's era machine. So I have no idea if the 3550's gear ring is still serviceable.
Ive attached some photos of the gear ring and starter motor. If you look at the gear ring it looks like the starter motor is failing to engage fully into the gear ring. I'm wondering if the burrs on the gears are causing the bendix gear to kick back and fail to fully engage? Maybe I could file down the gear ring? Or is the bendix gear spins up too high while trying to fully engage?
I bench tested the starter and saw that the bendix gear does fully deploy.
I wonder if there is a different style of starter motor that will throw the bendix gear to it's fully extended position before applying power to the motor? Seems like this should allow the gears to fully mesh before the starter starts spinning up.
So, when it was assembled, and you tried to start it, what happened? Did the starter go at a high speed, and sound like it ground on that flywheel a bit, but the engine didn't turn over at all (or just a little)?
I would first measure how deep the flywheel gear is from the mounting surface, and compare it with the starter. Maybe somebody put the wrong starter on it, so it just barely catches the edge of the flywheel when extended, instead of being centered on it.
You could also try just cleaning & lubing the starter drive gear mechanism, as it may not move freely enough for the solenoid to reliably move it into place.