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Old 12-07-2016, 04:35 AM
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Predator 500/560 JE Piston

Hi everyone,this is my first post and I have been following the forum for a while now.

Now my problem is this,I know my way around a predator engine but I am currently stuck,I build my son a really nice/fast quad with some mods that I personally did on the bike,engine and suspension,I am currently building a JE 560 BBK for myself,but this kit I bought from another guy that never finished this project before he past away,the Piston is brand new ,the cylinder is already correctly rebore to the size,I installed it and started it no problem,but as soon as the engine starting to heat up I can hear a knocking sound and becomes louder the more it heats up ,I suspect it is coming from the piston kissing the valves as it start to expand, I used the original OEM gasket ,was I suposed to get a thicker gasket with the JE Piston or do you use the Standard gasket?

The only way is to open up and measure or look for contact on the piston and valves,but maybe someone else already had this problem,I don't know if they previous owner decked the cylinder,my son's bike read 850 kPa/123 PSI with the 12,5 to 1 wiseco high compression piston standard 99,2mm bore ,running 95 Unleaded pump gas.

My 560 JE read 995kPa/144 PSI with decompression still installed,which I think is way to high and just for the the record ,I calibrate my compression gauge with a dead weight tester so it is 100%.

I did remove the decom. valve today to rule out noise from there, still the same,rechecked valve clearance ,Inlet:0.15mm ,Outlet :0.27mm, swapped cams with my son's bike ,the head is standard 126,4mm.

Thanks for the help
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Old 12-16-2016, 08:00 AM
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Just a thought here what is the clearance of the piston to cylinder wall, you may be getting piston slap also has the cylinder been sleeved or is it an aluminum cylinder that has been plated. I ask because sometimes guys will overbore an aluminum cylinder and think it is fine and end up destroying the cylinder as it wasn't plated.
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Old 12-19-2016, 01:28 AM
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Thanks for the reply,I think that is exactly what happened,the cylinder was cracked at 2 places.
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