084 flywheel key problems

[nba123]

I keep breaking the key on my 084. The saw is built and I race it and work with it I used to run the timeing advanced all the time with red locktight but started haveing trouble with it spining when working with it. I then stuck a key back in it and ran stock timeing but have broken 3 keys in the last year, the third being today. Any suggestions are welcome. Thanks James

 

[blsnelling]

Have you tried removing the key and lapping the flywheel onto the crank for a perfect fit? Perhaps your flywheel is damaged in the taper.

 

[nba123]

Have you tried removing the key and lapping the flywheel onto the crank for a perfect fit? Perhaps your flywheel is damaged in the taper.

It does have some scaring from the key fragments. R u talking about a coumpond of some kind.

 

[blsnelling]

It does have some scaring from the key fragments. R u talking about a coumpond of some kind.

I was thinking of something like valve grinding compound. I would think you may want to replace it with a new flywheel though. Each groove in it is that much less surface area to grip the crank. I'd also make sure to torque it to factory specs.

 

[nba123]

I was thinking of something like valve grinding compound. I would think you may want to replace it with a new flywheel though. Each groove in it is that much less surface area to grip the crank. I'd also make sure to torque it to factory specs.

I would really like to run advanced all the time with no key, also my flywheel is shaved a little but I dont know if it really helps. So to run advanced all the time what do u suggest. Thanks James. I will get a new flywheel.

 

[pioneerguy600]

Brad is right, you can use valve grinding compound to lapp the flywheel to the crank taper. I have done 3 that way and it works really well. Turning the flywheel by hand was a chore so I hooked up an adapter and turned it with a 1/2" electric drill. Once all the marks are removed and a good fit is felt then you need to clean the inside of the flywheel bore and the crank stub of all gunk and leave both surfaces absolutely clean and dry, brake cleaner for the last bout of cleanup and dry with comp air.
Pioneerguy600

 

[a. palmer jr.]

I'm wondering if those are set from the factory with an "interference fit", that is a slightly different angle on the flywheel as is on the crank. Of course when you turn it or lap it you are removing the interference fit and making it easier to loosen the next time. Just a thought.

 

[blsnelling]

You can thin the protruding part of the key about half and get an easy 10° of advance. It makes it far easier to index correctly too.

 

[pioneerguy600]

I'm wondering if those are set from the factory with an "interference fit", that is a slightly different angle on the flywheel as is on the crank. Of course when you turn it or lap it you are removing the interference fit and making it easier to loosen the next time. Just a thought.

Great thought but no the tapers are the same, the pressure from the nut forces the two tapers together with great force and it needs both surfaces to be in contact for the full length of the taper in the flywheel to keep it in place. The key plays very little with keeping the flywheel in position, it is there to position the flywheel and that is about all it does, once the nut is tightened down to spec then friction is what holds the two pieces in place. Lapping the flywheel to the crank provides the best mating surfaces, smooth and equal take along the taper = the best friction fit.
Pioneerguy600