Stihl String Trimmer Flywheel Slipping

[Skywatcher]

Greetings All

Just had a Stihl FS80 in my shop that wouldn't start, it would pop occasionally out of the muffler but that was it. Turned out the cast in key of the flywheel had sheared and the crankshaft had slipped in the flywheel retarding the ignition timing. This is not the first one of these I've run into, and I'm sure it won't be the last. Does anyone know how the clutch gets loose enough to allow the flywheel to slip (the flywheel is held on by the clutch)?

I simply filed a slot in the aluminum flywheel where the key was, then modified a ⅛" x ¼" woodruff key to fit the flywheel and crankshaft. Would anyone happen to know the correct torque for the clutch onto the crankshaft? I just gave it a quick zap with my ⅜" impact wrench. All the best,

Sky

[KE4AVB]

Probably the previous tech didn't torque it down to 15.5 ft-lbs. I have been working these Stihl trimmers for the last 11 yrs and never seen one with a sheared flywheel key.

[mr-moe]

Same here after 27 years at a Stihl dealer, I've only seen half a dozen keys sheared.
Mostly by shade-tree mechanics, that thought a torque wrench was only for head bolts.
If torqued properly it will never slip.

[38racing]

I think I may have one. Fellow dropped it off last year. Testing it all I got was a backfire. Been sitting since. Also had issue on a ryobi. Iirc I couldn't figure out how to hold things to get it torqued.

[KE4AVB]

If the Ryobi clutch is like this.

You make you own tool out of a large flange head from a MTD spindle. I got two these modified nuts as there is a large and small version of this clutch. And usually a deep well socket gets things torqued along with a piston stop.