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Piston readers here..

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This is the previous piston from my 01 kx 125 (didnt blow) and was sitting here wondering if anyone has a good eye for diagnosing my piston and if they could tell if its lean or rich. thanks.. had 42 hours on it.

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DSC01046.JPG

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Looks like compression was getting past the ring, but I have no idea what caused that gouge in the first pic though

yea thats what i was trying to find out, but to me all the different signs all look the same :/

Edited by NzJohny

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Just had a closer look, seems to be still there :)

Okay, so the engine ate something at one point or another. Seems you got off lucky. Make sure to have a good look at the cylinder wall.

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this bike had 35 hours on this piston when i brought it, i did the top end at 42 hours and had the cylinder re plated aswell.... cylinder 3.jpg im just trying to get my head around how it could get like that. 15.JPG  this is a picture of the air filter when i brought it. can dirt dirt really do such damage??

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The plug is a much better indicator of mixture.  It looks like there are cracks above the ring land in the crown, which indicates significantly excessive piston crown temperature.  The exhaust side of the piston also looks like it was getting particularly hot.  This could be due to a lean mixture, incorrect ignition timing or even excessive carbon buildup in the pipe.  After 42 hours the piston should not look that bad.

 

I don't see any signs of dirt getting in there.  You'll usually see vertical scoring where the particles get between the piston and bore.  That wouldn't cause this kind of problem anyway.  Dirt will kill the main and rod bearings first and foremost. 

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