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Alright folks, my 89 Big bear backfired and died. Got spark, got gas, seems to have compression, (but haven't tested it yet...next). She rolls over good, maybe too good...seems soft. Have spark and enough compression to blow gas mist out the plug hole when cranking. Suggestions, Been running great since we got it. Now, she just rolls and rolls....Please help!

99463
 

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Some of these older machines were known to shear their flywheel key. This would cause a no start situation even though you have spark and fuel
 

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Everything is rolling over. If the flywheel key was sheered the flywheel wouldn't move, correct?
 

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Everything is rolling over. If the flywheel key was sheered the flywheel wouldn't move, correct?
If your flywheel key is sheared the flywheel will still be tight on the crankshaft as pressure is maintained by the nut, but your ignition trigger will be out of phaze, witch means your spark plug will not fire at the correct time.

Just a thought as this has been brought up multiple times on these older style air cooled machines. I'm not very knowledgable on this Gen of atv
 

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If your flywheel key is sheared the flywheel will still be tight on the crankshaft as pressure is maintained by the nut, but your ignition trigger will be out of phaze, witch means your spark plug will not fire at the correct time.

Just a thought as this has been brought up multiple times on these older style air cooled machines. I'm not very knowledgable on this Gen of atv
Everything is rolling over. If the flywheel key was sheered the flywheel wouldn't move, correct?
 

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First, tried to reply threw e-mail, apparently I have to be on forum to reply. Thanks Vincent. That makes sense. I'd like to check this. Is there a way w/o tearing it down? How about trying to hold flywheel through the sight hole, and seeing if it will turn when I roll it over? Just a thought. Or do I have to crack the case?
 

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Not sure what is required to check the flywheel on those models. My experience is all on the later 550 - 700 grizzlies.

YouTube would be your best bet
 

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Not sure what is required to check the flywheel on those models. My experience is all on the later 550 - 700 grizzlies.

YouTube would be your best bet
Just a guess here, but is there a sight window to check timing on this machine? With piston at TDC would you not be able to see if flywheel is out of time?
 

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Looking at the timing Mark's through the sight hole will not matter any. The timing marks will still line up because they are held in time by the chain.

The only true 100% foolproof way to inspect the flywheel woodruff key is to remove the flywheel.

Btw, your Big Bear is giving you classic signs of a sheared flywheel woodruff key. I would bet its sheared.
 
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