I'm not sure that I have a 158 tooth I've read here that's usually 153 (?), anyway I have a 350 1 piece rear main seal from a 1987 chevyvan , bolt are not staggered.

I've buy a 1987 Camaro starter.. even with shims nothing .... seems the spur gear jamming in the flywheel and the starter spin really slowly


Help... it's the 6 month I'm on this build and I have no idea of the problem at the moment

 

The 153 tooth flywheel is a smaller diameter flywheel, and is generally found on 305 engines. It's used to fit into the smaller tunnel of cars like F-bodies. It also fits into the small bellhousing of the T10 for example.
The 168 tooth flywheel is a larger diameter (over 1" larger), and is generally on 350 and larger engines.

If your starter will kick out the bendix and will engage the teeth of the flywheel, it's the correct match. If you use a 168 tooth starter with a 153 tooth flywheel, the teeth won't even touch, and if you use a 153 tooth starter, and a 168 tooth flywheel, the starter won't even bolt up.

You can post a picture of the jamming if you want, that might help clear it up. I'd guess you just have the starter wired up incorrectly. Is the engine on a stand right now?