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250r builders

2K views 4 replies 3 participants last post by  acecarlos 
#1 ·
what cause this ?



cylinder had 3 .020 base gaskets under it...for what i dont know..piston did not come all the way to top



is this standard size piston....has #50 on top
 

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#2 ·
Looks lean by the looks of the head color and piston damage and With 3 base gaskets there is a strong possibility that it had a sizable leak causing the motor to lean out . You better check the crank real good for damage from all the aluminum that has went thru the bottom end because of the hole melting in the side of the pistonNew bearings and seals would be a good idea when large amounts of aluminum pieces run threw them, very hard to flush it all out.
 
#5 ·
To the OP:



Air leak, detonation, timing to far advanced, ect...your CDI could have gone, or the engine was detonating (bad fuel, octane too low, ect...), air leaks at the left side main seal or just about any other place.



Your piston looks like a 66.50 MM (+.50)cast ProX, ART or Honda. These are very good pistons, you do have options for a Forged piston set from Wiseco or Wossner. Stock bore is 66 MM, 66.25 MM and 66.50 MM are the next two bore sizes...you can go to 69.50MM with standard 250R piston sets. try a 66.75MM if the bore will clean up or a 67 MM.



We stock all these piston sets for Honda 2 strokes.



Carlos
 
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