Maintenance & Technical > KX500 Original

86 kx500 resurrection

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harveson1:
Hi all. First time post. I am struggling with a 1986 kx500. I bought the bike non running. I had the cylinder re-plated.  Put in a new wiseco piston and rings. My ring end gap is .45mm. After the new top end, my compression read 60PSI and would not start, so I had the head modified to reduce the squish to 1.5mm from 2.5mm. The compression jumped to 120PSI and I also learned to jump on it with all i got :-). I got it to start once with starting fluid by some act of God. In general all I can get it to do is back fire out the exhaust.  I did check the wood drift key. I rebuilt the stator. I did replace the reed petals with new boysen reeds. Now I am thinking about the crank seal because i have what seems to be an excessive amount of oil in the cylinder, on the underside of the piston, oil in the combustion chamber, and oil leaking out the exhaust. I did a leak down test with the piston at BDC and did not see any leakage from either seal on the crank. My biggest leak was from the intake carb boot cracking. My leak down test read 30% at 8-10PSI. Just seeking advice before split the cases to get to the seals. Thanks in advance

sandblaster:
120lb is not good.. You need to be in the 180-190 for a new cylinder.
It's a common problem for those putting a newer 89-04 piston in a pre 89 cylinder.

harveson1:
thanks for the reply. I guess i will pray, hunt and kill for a stock 1986 piston, since that seems to be my only option.

sandblaster:
Tom Morgan at TMR can cut your head for the correct cc.
Or, you can have your cylinder decked.
Either way will get you the right compression.

harveson1:
Sounds good. Thanks

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