hi all. i am not an 2 stroke expert. i heard a knocking noise in my engine - i assumed engine because the bike makes this noise while in neutral, and while in gear. it is like something is loose, so i had the piston and rings replaced - not an easy task in australia on an imported bike, but i got the parts... while the bike was there, i got a heap of work done - front and rear suspension stiffened/rebuilt, new brakes, tyres then as soon as i rode the bike home, the noise was still there. i had the mechanic check the big end bearing tolerances and they were well within. i have spent too much on the bike now to give up - any advice on where to go now? could it be a counterbalancer problem? is this common on crm's?
the bike still runs fine - all but this annoying noise. i'm still clearing tabletops, wheelieing over rivers and keeping up with / occasionally passing friends on yz250f's and wr and xr 400's
thankyou, and great work on the site paul. more pictures/stories etc... coming.

I have 3 words for you...

Balancer shaft wear.

I hope it's not that, but that's what it sounds like.

Chris

Mine makes a knocking noise if I dont warm it up first (probably not a prob in oz) but once warm it sounds lovely. its been like this since I got it 17months ago and never got any worse.

balancer shaft wear... that sounds pretty scary. the bike only has 12000km on it - about 6000 miles - but who knows if they're legitimate.
i might take a look at it one rainy day.
thanks, graham.

I thought it might have been just me that had had balance shaft problems.
My Mk 3 is on its third and has only done about 15,000 kms, mostly off-road.
I knew it had had a replacement shaft fitted before I bought it, and it went again shortly after I bought it. (I believe that the replacement was a used shaft so it may have been on its way out already.)
You will know when the shaft is starting to wear, the bike sounds like a bag of nails particularly on the over-run.
You have to take out the clutch to get at the nut on the end of the shaft and then slide it out from the other side of the engine.
I am right out in the wilds here and so the only time I have done this job on my bike I had the engineering department of the company I work for grind the bearing down, hard chrome it to oversize and then grind it back to the correct size. It was a damn sight cheaper than buying a new one and several thousand kms later it is still going OK.

If it knocks intermittently, my does the same. I have replaced the mains, the balance shaft and bearings, all the gear box bearings recently as the mains went, however the intermittent metallic knocking still occurs! Mine has been doing it for 18 months, and no doubt it will carry on doing it!
If you feel the need to change the balance shaft as is being suggested, its not all that bad (well if you can get the bits over in sunny oz). Over here the balance shaft is about 70 quid, and the 2 bearings add up to about 25, theres also a seal that you need for about a tenner. It is possibel to fit the lot without removing or splitting the engine, but I will warn you the needle roller in teh left hand side of the engine is a bastard to get out. On a mates bike, we resorted to a dremil to grind it out! Oh you will need a clutch case gasket as well.
Hope this helps

Who's there ??

Sorry, i'l get me coat

Those pesky kids......................










Knock - run, oh never mind!

*cough* *cough* although i dont admit it, im still regarded as a kid

thanks. i think i will eventually end up buying a new yamaha. as much as i love to ride the crm, it's just a headf*#k trying to find parts and someone who knows how it all goes back together. Still, i don't think i will sell the bike...

I dont think the noise in my bike is the power valve, i cant see any wear patterns indicating contact.
Is it the gear teeth or the bearings that wear on the balance shaft, because the shaft itself should not be in contact with anything? I havent taken the shaft out, but i would presume that the gears and bearings can be removed from the shaft, which would reduce the costs getting rid of this rattle as only the faulty part need be replaced.

If the 'knock' gets any worse in my bike i will try upgrade the faulty parts.
Has anyone out there tried this?

The balancer shaft itself wears at the journal nearest the balance weight. The shaft has been made out of a steel grade too soft for the job and as the balance shaft is (by definition) running out of balance, it is causing wear on one side of the shaft.
If you look at the shaft you will see wear lines forming on the side of the shaft that has the eccentric weight. It doesn't take much wear to make it sound like a bag of nails.
You are correct that all of the starter and clutch bits can be removed and replaced, and you only need the balancer shaft repaired or replaced, but you had better check that the bearing that the shaft runs in hasn't been damaged. You should also not re-use the clutch crush nut according to the manual but you will get away with it if you remove it carefully.

Cheers