starter problems

[Lasalle_mh]

have 87 generac gn 410 np50g generator and starter bendex will engage at time w/o problems other is goes up then drops down like it lost power or jams under the fly wheel, have tried using different shims but still same problem, starter has been replaced last spring

[azrving]

You say new starter but I have seen new starters with old drives. If the drive /gear is weak it will keep kicking out. The gear drive acts as a one way clutch so it can drive yet it has to be able to slip when the engine fires up and the drive drops out. If this friction is not right it will too easily drop out. As mentioned check the ring gear for any worn areas.

[mabynack]

You might also try putting a little grease on the starter shaft where the bendix rides. Check the bendix gears to make sure they aren't broken or chipped and check the ring gear on the flywheel while you have the starter off. You also can check for loose connections at the battery and starter. Sometimes low voltage at the starter can cause the starter to not engage fully.

It's also not unheard of to get a bad new starter. I worked on a crane once and we had to partially pull the engine to get the starter out. I spent more than half a day replacing the starter and when we went to start it, the new starter was bad.

[gatorcq]

see if you can spin the flywheel. If it works then bad spot.
If it is flywheel, either replacing it or remove and rotate it