Out for a scratch yesterday,all was going so well until the motor stops while
flat out in fifth gear. I coasted to a stop and tried the kickstart,yes it was locked solid I pulled the lower plug,and it was very "white looking"!Got the bike home and removed the top end,expecting damage,but it all looks fine.The upper plug was in the same condition as the top one.I cannot rotate the crank ! There was nothing suspect came out when I flushed the case.Doesn't look good does it Would a weak mixture break the crankshaft? And not cause cylinder damage?

It could... it's unusual for a crank to go before a piston, but it can happen.

Take the flywheel cover off, make sure you're in neutral, and see if you can turn the flywheel by hand.
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I've tried to rotate the flywheel,no joy!i had the impression that a weak mix would cause top end damage first,in this case it looks like i'll have to pay for my education!

It's certainly more common for the top to go first, but like I say, not impossible for a crank to fail.

I'd take the clutch off next, to isolate the crank, and see if it turns then. It sounds suspiciously like the crank if the pistons look OK but the plugs are white, but you never know!
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Could the gearbox have locked up?
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Well, that's kind of what I was thinking/hoping. A transmission is far less severe to fix than the crank, but white plugs are a bad omen.

The idea of removing the clutch assembly isolates the crank from the transmission. If it turns, then it's likely a transmission fault... if it doesn't, then it looks like the cases need to be split.
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I'll remove the clutch from the equation and see,not hopeful though.

o o


Last edited by DifferentStrokes on Mon Sep 28, 2009 10:43 pm; edited 1 time in total

That's not true is it? It only means the clutch is (or at least should be) disengaged. Removing the driven gear however completely isolates the crank.
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o o


Last edited by DifferentStrokes on Mon Sep 28, 2009 10:43 pm; edited 1 time in total

It may be the hard way, but my point was to isolate the components. There may even be a problem with the clutch mechanism. If the assembly is removed (easy enough if it's wet, but admittedly a bit of a pain if dry) then it eliminates it from the equation. Don't you think I would've thought about just pulling the lever in? Pulling the lever still leaves rotating components in contact with one-another.

It won't cost anything other than a little time.

Maybe I just prefer to be thorough? I imagine he's already tried to roll the bike with the clutch in. I'm sure most would in these circumstances.
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o o


Last edited by DifferentStrokes on Mon Sep 28, 2009 10:43 pm; edited 1 time in total

what you talkin' about willis?

bushman wrote: flat out in fifth gear. I coasted to a stop and tried the kickstart,yes it was locked solid

It rolls with the clutch in, otherwise it'd have locked solid at 100 odd mph and slid to a halt unless you could click it into neutral which'd probably involve using the rear brake to remove the load from the gearbox, no one would think of that whilst skidding at 100mph.

Absolutely clutching at straws but removing the drive from the crank (and I guess you should also remove the flywheel just in case something has got in there) then trying to spin it will totally establish that the problem is inside the cases.
Plus that's all got to come off anyway.
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Andy wrote:It's certainly more common for the top to go first, but like I say, not impossible for a crank to fail.

Quite right Andy, I can speak from experience. When I stripped my motor down, the pistons and cylinders were ok, in respect to not ever having seized, albeit some general running wear. The centre crank bearing however was a slack as a bag of Knackers. The flywheel side bearing also had serious play in it too. If I'd continued to run the bike, one of those bearings would have collapsed / seized for sure way way before a piston grabbing due to running lean. My plugs were a nice dark tan brown.
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