Small Engines (Lawn Mowers, etc.): starter gear, craftsman model, flywheel

Question
-Marc, I changed the starter gear last week,it was totally stripped out, it ran for a few days then the gear snapped so I looked at the bendix and it was wore too so I changed the whole thing, called the starter drive. Ran one day and it snapped another gear, acts like it isn't disengaging from the flywheel or maybe the flywheel is not turning fast enough or something...any idea why the starter gear doesn't disengage with all new parts....Thanks alot  Wanda----------------------
Followup To
Question -
I have a sears riding lawnmower, it broke the starter gear, I replaced it, broke again so I replaced the starter drive and gear. Now it has broke again, it is breaking the plastic gear,so I think maybe the flywheel may be stiff not turning freely, I can turn it with my hand. This is a 19 H.P. craftsman model 917.270770. Do you have any ideas what might be happening. This tractor is about 5 years old, hasn't had alot of trouble with it until now.
Answer -
It is more likely the starter gear is getting broken because it isn't properly disengaging from the flywheel when the engine starts.  Make sure the bendix is properly engaging the starter gear with the flywheel and is allowing it to retract properly once the engine starts.  This problem is usually caused by either the bendix being dirty or worn badly.  You can usually get an entire bendix drive and starter gear kit, depending on the engine model.  Hope this helps.

Answer
The only other things I can think of are that the flywheel ring gear is contaminated (dried grease, oil & dirt, etc) that is causing it to hold the starter gear or there is a problem with the starter mounting location.  The problem with the mounting location may be due to a loose fastener, wear or some type of misalignment that may require the starter mounting bracket be shimmed to correct it.  If you remove the shroud and engage the starter gear into the flywheel ring gear by hand, it shouldn't be binding and should have a slight amount of clearance (and backlash), should be level with the ring gear and the teeth should be parallel.  Hope this helps.