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Discussion Starter · #1 ·
Today my motor started making a bad grinding sound and it had alot more vibration then it has ever had. It only makes the noise when letting off the throtte, or while there is no load on the back wheel, like in the air. First i though it made have been the chain becuase it was a little loose (but not anywhere near as looose as ive had it before) but it was doing it in netruel (but not as loud as when in gear) to so i doubt its the chain (i even held the chain while it was in netruel so the chain couldnt move at all. I coudlnt tell if it was coming from the cylinder or around the flywheel, but im pretty sure the sound was coming from the sprocket side of the motor. The sound went away for a while and then came back, then went a way angain and cam back. It just wouldnt stay long enough to find out what it was, but it was consistenly (sp?) there. I have never heard it make this sound ever before. What could be causing this sound and vibration?



Oh and by the way, the only mods to my motor are a 88 S-stage.
 

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Discussion Starter · #3 ·
I dont have a skid plate on my bike, It didnt sound like it was coming from the head, but like i said it was hard to tell. I held anything that could shake (platic, carb, cables etc.) Im almost a 100% sure its the motor or front sprocket/chain, but i doubt the sprocket or chain would cause vibration. Or could it?
 

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You may also have a weak or broken valve spring. That would explain the noise with no load and when you gas it in the air. Valve float. I've had them go soft(before they break) and produce the sound you describe. Usually it's the intake valve spring.
 

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I had the same type of thing happen to me. When i stopped the motor i tried to kick it back into life umteen times.... hardly firing but making a horrible grinding type noise. It turns out the woodruff key had sheared and naffed my fly wheel with scores. how it carried on running until i actually stopped it i'll never know.... i doubt yours is the same problem as you can still kick yours into life but its deffo worth a look.
 
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