Cracked shaft on flywheel

[rsm]

what would cause this

 

[ILENGINE]

Most common is use of a steel key instead of the aluminum key on Briggs, Could of also been cause from the flywheel over torqued causing cracks to form in the taper.

 

[PTmowerMech]

I had of these a few months ago. It actually wideneed the gap in the crankshaft keyway. I wrapped the new flywheel key a couple of rounds with tin foil. Customer hasn't called me back. So I guess it's still good.

His key was stretched and bent out of shape, instead of breaking.

 

[tom3]

There are magnets under that flywheel that maybe came loose and jammed under there, locked the motor and the flywheel inertia created the mess. Just guessing.

 

[bertsmobile1]

Most common is use of a steel key instead of the aluminum key on Briggs, Could of also been cause from the flywheel over torqued causing cracks to form in the taper.

Or some one hammering the wrong key into the slot .
To answer the exact question, why it happened is because the boss was subjected to a higher tensile strength than the gray cast iron can cope with.
What were the circumstances preceeding the breakage ?

 

[StarTech]

Actually I just replaced a flywheel with the same damage on a 31C707-3346-G6. It is old style with tapered keyway. NO one has touched the flywheel area since new and I have been the only tech to work on it.

Since Briggs already has service bulletin out of these key ways and have redesign both the flywheel and crankshaft key ways. I suspect the flywheel was under torqued since Briggs change from 100 ft-lbs with aluminum key to 110 ft-lbs with a steel key. The engine I was working on had an ACR failure cause metal to get in the gear teeth and also damaged the oil slinger / governor assembly.

Kinda a hassle to replace since the flywheel for the above engine is NLA but I was able to use an older 31C707 flywheel and fan to effect the repairs.