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300xc still won’t start...do flywheels go bad?

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All I have tried everything I can... please help!!! I have a ride trip this weekend planned!

 

Long story short: bike ran great, started ok after sitting and amazing hot (electric start only, never used kicker in two years). 3 weeks ago I tried going to a ride around the yard, started (after a long time) and idled great, went to take off, stalled it, hasn’t started since. Not with electric or kicker. Kick starter has a hard kick back after a few trys, but maybe that’s normal, as I have never needed to kick it, I do not know.

 

I have the full service manual. I have done every electrical check I can without running, all check out. I have spark per a spark tester, I have brand new plug, gapped correctly. I have checked with kill switch disconnected, I even installed new kill switch.

 

I have a wet plug, I have puffs of smoke out the exhaust, I have compression of 185 psi. I have cleaned carb multiple times. Still nothing.

 

I replaced the coil and plug boot bc it was cheap. I replaced the stator (with a trailtech DC high watt) bc Slavens said it may be that, as the can show correct resistance until complete failure...still nothing.

 

I have checked the flywheel key does not look sheared.

 

Any thoughts? My last thought is a flywheel issue. Do they go bad? Do the lose magnetic force? It looks like a welded two piece unit. The part I think is the “trigger” looks like it is “burnt” or “corroded” a bit. I often see little pieces of something between the two flywheel halves. IMG_1651.JPGIMG_1652.JPG

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Ok well 3 weeks later 30 minutes after this pleading post for help, I found the issue!! I “thought” the flywheel key looked good, bc I took the nut off. Then just now I remembered where the flywheel puller was, pulled it off and yup...the flywheel/crank woodruff key sheared!!! Now the question is...why? And can I hand file/emery cloth the crank, new key, and keep riding?IMG_1653.JPG

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Yes. Polish it up as nice as you can and replace the key.  A few drops of loctite on the shaft will help. Cam.

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Wonder if I caused this as last time I removed flywheel for starter  housing cleaning/maintenance, I greased the shaft taper.  I assumed the key did the holding.

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They usually shear because the flywheel is loose on the shaft.  All the key does is align the flywheel while you are installing it.  torquing the flywheel onto the taper is what provides your holding force (and why you need a puller).  If the key provided enough support, then they could use a (cheaper to manufacture) straight shaft and bore.

I don't think your greasing the shaft caused this, but it didn't help.  My guess is you under-torqued that nut and it backed off, allowing the flywheel to hammer the keyway till it broke.

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This is almost exactly what happened to me, except i was ignorant of Flywheel Keys.

My nut backed off while riding, taking enough tension off the press fit to allow rotation/sheering.  I chased issues and gremlins for months trying to track down the problem.  finally found this, replaced it with a new $0.95 key and the bike started first kick.

Chalking it up to "live and learn" personally.

Glad you found it.

 

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Yea, this one was really troubling me, nothing was solving the problem.  It wasn't until googling about the hard kick back while trying to kick start that led to different forums mentioning the crank key...and there it was!

Now I will be getting some lapping compound on the way home, they make a special Loctite 648 special for tapered shafts, but I am concerned to use it as if I need to take off in the future it will be very difficult without heat which could damage the magnetic force of the flywheel.  

What are thoughts on the Loctite on the shaft?  I know stock they are supposed to go on dry, no Loctite and if I can lap it good together than ideally it would be just like new....

Edited by Ss65supernova

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I did not locktite the shaft.  I DID locktite the nut.  As long as the nut is torqued properly and stays put, that should hold the shaft as its designed to.  

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OK, and did you re-torque after a heat cycle of the engine or anything (and then re Loctite obviously)?  I am very particular on torque, I even send my torque wrenches out to get re certified and triple check everything haha....I must have done something wrong though this time.

Edited by Ss65supernova

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Grease takes up a surprising amount of space and is harder to squeeze out than you would guess, I think as it squished out over time / heat cycles the flywheel got loose.

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"Do the lose magnetic force? "

I had a KTM loose the magnetism in the stator and it had to get re-energized as the fix, so yes, this can happen. Often? I do not think so.

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I would lap the flywheel and crack together with some fine grinding paste. The taper needs to be a very precise fit to not work lose.

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13 hours ago, NZracer said:

I would lap the flywheel and crack together with some fine grinding paste. The taper needs to be a very precise fit to not work lose.

I would only do that to this particular crank, and even then I'd be hesitant.  Do the minimum you can to clean up the damage, then go from there.  You're not making a machining spindle, just locking two parts together.

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So, I have been lapping the flywheel to the crank....what I do not know is how far the flywheel is supposed to sit on the crank.  What I mean is there is the flat face of the flywheel and the flat machined surface where the OD of the crank gets smaller and turns into threads.  The flywheel will not push back flush with the flat front face of the crank, it sits out a very tiny amount.  I measured it to be about .030" (.77mm) But is that correct, I do not know? When the nut is torqued down, it may pull it tight, not sure.

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I think I answered my own question. Flywheel needs to sit somewhat outside of crank or else when you tighten nut down it won’t pull the two tapers and lock them. So I think I’m good!

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