Small Engines (Lawn Mowers, etc.): Craftsman riding mower model 917.256490, clutch assembly, cone shape

Question
The mower will crank fine & ran in reverse with no problem.  The second I put it in forward gear it backfired once & sheared the flywheel key.  Any ideas?  

Answer
Hiya Bill
Quick question.
Has the flywheel recently been removed for any reason?
If so.. I am concerned about the following.

There should be a large washer underneath the retaining device for the flywheel, be it a large nut or a clutch assembly.  This washer is bent into a slight cone shape, which gives it a spring quality.  Sometimes folks leave this off, thinking it is damaged, or replace it with a flat washer.  If it is missing or not cone shaped, the flywheel WILL loosen at some point and shear the key (it won't take long).

Other than that- your key could have been partially sheared for some time- a failure waiting to happen.  WHen you replace it- make sure about that washer and torque the flywheel retaining device to roughly 70ftlbs (about all you can muster at the end of a 1/2 standard length ratchet).

Lemme know how it goes!