Flywheel key sheared, ms250

[tilenick]

I have had my stihl ms250 for about 10 years, bought it new. it started over-revving one day and I figured the impulse line, the intake boot, or the fuel line had rotted a hole in it. It has never missed beat until this fall, and when I took it apart to fix/look at the rubbers I noticed the flywheel looked out of place. I removed it and saw the key was sheared off the flywheel. I was wondering why this might happen, I have never had It apart before today.
Thanks,
Nick.

 

[Sameoldclifford]

My MS250 flywheel sheared because I forgot to tighten the nut after a teardown (after 25 years of reliable service). Needing a quick solution, I chiseled out a keyway on the flywheel, ground a key from a scrap of brass, placed the flywheel on the shaft and tapped the key in from the top. Seems to work fine, maybe better than stock. The cast-in-place key seems like a weak element in an otherwise brilliantly designed machine. Then again, it wasn't a problem until I stuck my nose in it.