sizing piston kit/top end rebuild

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pne
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Joined: 06:48 pm Mar 21 2015
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sizing piston kit/top end rebuild

Post by pne »

Hi guys, I just bought a 96 kdx and started tearing into it. It wasn't revving out properly and I spent the last day rebuilding the KIPS valve. I remember how painful this was from my 98 kx250 I owned a few years ago. Unfortunately the o-ring on the one rod that actuates the subvalve got caught and torn. Does anyone know if this is important? I wonder if it would cause an air leak if run without, although without it the KIPS is butter smooth.

My second question is regarding the piston sizing. I mic'd the bore and got the following figures, not sure how to size a piston based on them, how much piston to wall clearance is required? I took 3 measurements at the top, middle and bottom of the cylinder. The bike has an unknown history I'm not sure if the cylinder was ever recoated. It might be worth noting that the engine is very noisy at idle, sounds like knocking or piston slap.

A) 2.6237 x 2.6216
B) 2.6248 x 2.6250
C) 2.6215 x 2.6215
canamfan
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Location: butler mo USA

sizing piston kit/top end rebuild

Post by canamfan »

according to the manual you should have .079-.089 mm piston to cylinder clearance or .003-.0035 in thousands of an inch. It says to measure at the bottom of the cylinder. You measure the piston on the skirt about level with the bottom of the piston pin hole. You measured 2.6215 at the bottom which is 66.59 mm, standard piston is 66mm So you would have .59mm clearance or .023 which is to much clearance. There were slightly oversize pistons available. I looked and wiseco shows a .5mm oversize piston which would give you .09mm clearance which is right at the top of the max clearance so if the plating looks good you could go that way. Good luck, I'm going riding to nice a day to miss out on that.
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