I did something stupid on my Sears Ride On with Seafoam...

[mcfarmall]

Solved: It was the flywheel key. How it broke I don't know, never hit anything. I'd like to thank all of you for you saved me from getting a new ride on. Thank You Thank You!!!!

A strong backfire can compromise the integrity of the flywheel key.

 

[whitepine2]

Hitting a fixed object,stone,wood etc.can bend or break a key ask me how I know.

 

[crazyal]

I can't count the number of sheer pins I went through as a kid. It seamed like I always had at least one go-cart with a horizontal 5hp Briggs engine that was cobbed together. More than one got replaced with a steel bolt filed into a square shape because I didn't have a spare. Having the correct washer and the nut torqued correctly also makes a big difference. Being 10 years old and trying to hold a flywheel by hand while a friend tightens the nut (which wasn't a typical nut since the pull starter connected to the nut) down doesn't really get it tight enough. Putting a screwdriver between cooling fins on the flywheel sort of works but sooner or later you will break off a fin or two.

 

[JRobyn]

I've always been able to remove small engine flywheel nuts by removing the spark plug and stuffing about 1/2 cylinder worth of soft rope (cotton is best) in it. Don't go too crazy with the torque, or you may wind up with a bent rod.

 

[Joebklyn]

The flywheel key was broken. I first had to get a gear puller thing to pull the flywheel off. Key was in 2 pieces. Got replacement and it started right up.