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Location: Ravenna, MI USA
OK a friend of mine had this issue with his oem piston at I think it was about 27 hrs on the piston. Any ideas how thus could have happened? A little background the bike was stock except fmf exhaust and a Ron Hamp port job and valves. We think we know what may have caused it but looking for others ideas. 
Yes that is the chunk from the piston that I found when I replaced his tranny gears to the updated gears, almost in the tranny area
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Could it be detonation?
Could the piston have been hitting the spark plug?
Wrong base gasket after port job?
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Was it mapped for that gas? 95 oct oxygenated gas with that high of a CR i wouldnt be surprised one bit if it was detonating as others said. Add in the exhaust and youre running lean most likely.
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Could detonation just knock out a solid junk of piston? I always thought it would burn a hole through it not knock out a solid chunk, but I don't know I've never dealt with any issue like that which is why I'm asking here. When I first saw it I would have sworn it hit the plug but he said no it didn't, definitely weird for me to see. Lol The bike is a factory edition and came with the exhaust, I think, like I said it's not my bike, so idk if the factory had a different map for exhaust but it was not mapped for the pro6.
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I would think if theres a split in the crack, it could blow out the center part. Detonation/preignition destroys pistons.
Personally i think it hit the plug even tho your friend says it didnt
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Was the Piston installed backwards, it just seems weird there's so much carbon buildup on the intake valve side. There's also a lot of marks in the top of that piston like something was sucked through the motor , I'm assuming the piece fell down and didn't go up because you found it in the transmission.
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pic of the wrist pin? almost looks like the 06 kx450f wrist pin issues when those bikes first came out.
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Heat caused that. It melted and started the crack from there.
Race Bike: 2018 KTM 350SXF
Other Bikes: 1985 CR80R, 1990 CR250R, 1998 PW80, Yeti SB130LR.
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I don't have a pic of the wrist pin. The piston wasn't installed backwards either. The only thing that was figured out to cause it was a lean issue. After he rubuilt it he took it to Hamp and put it on his dyno and it was 2pts too lean at top rpm and after 15 minutes of run time he would lose 4hp as the motor got hotter. Ron had said that his bike was running way leaner with the stock ecu than what mine ran on his dyno, so he is now ordering a vortex to fix the lean issue. That's what we believe is the problem but also idk if it had anything to do with it but his fuel pump also went out so maybe it wasn't pushing as much fuel as needed either.?.?
