Lawn mowers do tend to be simple but a nagging problem after hitting something like a root or part of a stump is very difficult or failure to start. If this happens make sure you check the key on the shaft for the flywheel as it is made to shear when something hard is hit. It doesn't take much deformation of this key to make it hard or impossible to start. Make sure you replace it with the RIGHT key as putting the wrong one in defeats the safety purpose of the key. They are made of fairly soft metal and are easily damaged. It should go in without the use of tools. Wood can be used to make sure it is seated in the keyway, if necessary. If you don't have a blade balancer, use a a bolt larger than the mounting hole with its end ground to a taper, or used a washer larger than the hole with a piece of string up through the hole to check for balance. The washer should be edge to the hole, not flat. It should be as horizontal as you can get it when sharpening it. Do not make the blade knife sharp as it will dull very fast and get out of balance and cause much vibration in the machine. Just grind enough to get the edge reasonably smooth and get the ruff nicks down to balance it, no knife edge.

It sounds like you're on to something! That would make so much sense, and I don't think Mark knew to check it. I'll have to ask him to peer under there --- I threw a fit after he fixed it when I discovered I still wasn't strong enough to start it.

Thanks you so much for sharing this information vester.

In case anyone out there is curious. A Briggs and Stratton fly wheel key part number for this mower is 222698 and the blade number is 189028. that's for engine number 123K02 series.

Model number for this Craftsman mower is 917.388571

Stay tuned for how the fly wheel puller tool works out in the near future.