Maintenance & Technical > KX500 Original

rattle from motor

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stroke.n.smoke:
A couple years ago I rebuilt my motor because it had a loud rattle at idle.  The bike still has the rattle at idle and its been two years.  It did need a rebuild as the crank bearings were not very smooth and the cylinder plating was peeled.  I got the cylinder replated and rebuilt the crank.  Do these bikes have a rattle at idle normally, once you rev it up slightly the rattle is none existant, but still worries me somewhat.  I am going to tear off the top end in the next couple months and have a look.  I rode with Snoopjon last fall and his bike rattles too, he figured his was louder than mine and I thought mine was louder but whatever, they both rattled.  Mine has a new motor.  Is this gear noise from the primary gears?  Or piston slap or bearing noise.  You can really hear it on video with the helmet cam, but like I said, it goes away quickly once revved up.  I had an old IT 465 that was this way too.  The motor runs strong still after two years and everyone says to not worry about it, but I do somewhat.  Mabye there is too much piston clearance, I used a wiseco and Max power replated the cylinder and fitted the piston.  I never actually measured anything before putting the motor back together, just trusted them...  I have run Amsoil Dominator oil at 40:1 for the last 4-5 years with zero issues but that rattle is annoying me to the point of another rebuild or something.  I have run everything from VP C12 and VP111 to pump gas and even Av gas with blends and octane boost/pump.  I have basically settled with AvGas LL100 octane (cheapest high octane) with 40:1 oil mixture.  Bike has run great.  I guess I will see what it looks like in a couple weeks when I tear it down, but if anyone has any ideas I would like to remedy the rattle while its apart.  I will be measuring up the piston and cylinder and checking the runout and crank clearances.


   

ID KX500:
Mine does it too,,, somebody jump in here with an answer please,,, I don't think anything is wrong however.

stroke.n.smoke:
I just did a quick search about the rattle and it seems that its normal.  I will have to talk with Snoopjon when he gets his back together and some hours on it.  Curious to see what it sounds like after his complete rebuild.

stroke.n.smoke:
Have a listen to the rattle in this motor, I don't think I will even tear into mine to inspect anymore.  Mabye a compression test and look through the exhaust port.  Mabye a new head gasket, but other than that I think mine should be fine.  Mine sounds the same.

http://wolbrinkrace.blogspot.com/

cbxracer30:
Just a guess but what about the clutch basket bearings on a CBX thats where all the motor noise comes from ?, pull the clutch in noise goes away .CBX

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