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Noise from counterbalance shaft?

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A friend has a 2006 WR250F that developed a noise that sounds like piston rattle / slap to us. I put a piston in it when he bought it and changed exhaust cam to YZ timing with shortened decompression pin. Rode it for a few months and it developed what sounds like piston rattle. The cylinder looked pretty good but I figured it had some wear so he bought an Athena 290 kit along with a new crankshaft / main bearings.  The noise is exactly the same as before so I'm thinking it would have changed somehow if it was crank / piston related. We can mainly hear it on deceleration with closed throttle. Haven't heard it on acceleration and quiet as it can be at idle. About all I can think of is either the counterbalance shaft needle bearing or the needle bearing on the clutch basket. Anybody got any other ideas?? Thanks, Clay. 

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In a car a noise that you are describing is a wrist pin. Only knocks on deceleration. Not sure if it is the same in a bike. I would think so.

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I agree but it all got changed - crank, main bearings, rod, cylinder, piston, cam chain and wrist pin and the noise is identical. It should have changed. Playing with it some today it will do it at a steady rpm - guessing around 4000. In gear / clutch in or neutral / clutch out makes no difference so I'm thinking not transmission related and thinking balance shaft bearing. The ball bearing felt good but I don't remember checking for loose motion on the needle bearing end. I can't really think of anything else that would make a cyclical / rattle noise. Just guessing but I'll know in a week or two. Clay. 

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Sorry Clay. I have nothing else. MC,s are kind of new to me and all I have is auto experience. We have a couple of guys in senior dirt-riders blab that are good. Make a post there and see what your response is. Good luck.

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Picked it up and spent some more time on it today. I'm thinking now it's clutch related. Steady rpm where rattle is - clutch out - neutral it's there. Clutch in - in gear - it's there. Barely engage the clutch and it seems to go away. Now I'm thinking needle bearing on clutch basket next. I put a clutch in it maybe 20 - 30 hours ago and it and the basket looked perfect when I did the rebuild. It is a Yamaha clutch so shouldn't be any issues there. If I figure it out I'll post what it was. Clay. 

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Pulled the clutch basket today. There is some rotational clearance between the drive gear and basket. Meaning you can hold the gear and turn the basket some with your hand. Don't know what has happened yet. Not sure if the springs have slightly collapsed or the spring pocket in the aluminum basket is worn, etc. I'll grind the rivets off tomorrow and see what's going on. Clay. 

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Update on this. Ended up replacing the clutch basket. This however wasn't the source of the noise. I pulled both side covers back off and didn't find anything. Noticed the oil looked much dirtier than mine after 5 hours. Dropped it and pulled / cut the filter. Filter shows there is definitely something going on. At least I'm not crazy. Started pulling it back down to go over it with a magnifying glass. Piston has more wear (even though it appears to be just the coating) on the intake side than I expected. Exhaust side is perfect and cylinder is perfect. Piston / cylinder clearance is between 0.002" - 0.0025". Cylinder is around 0.0004" out of round. Piston measures 82.96 at its largest point. It has a lot of rock at tdc but as short as they are I guess that's to be expected. I'll keep digging but this one has me stumped for now. Clay

 

 

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