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Help! XR600 smoking on new rebuild

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My XR600 has been dumping a very good amount of white smoke and unburnt oil from the exhaust. When I say very good amount, its enough to leave a nice smoke trail when I ride and will fill up my neighborhood with a large cloud. At first I figured it was the valve seals since I left the head off the bike dry for about a year before I re-assembled the motor. I changed out the seals and nothing changed. I just pulled the motor apart today to try and find the problem. The only thing that looked any different from when the motor was built was some scoring on the piston skirt from sand on the front side of the motor. The sand got in from using a foam unifilter in the dunes (never again!). Please also note that the bike was smoking as soo as I started it up after the rebuild before I took it to the dunes. The valve guides feel tight. Here is a breakdown of everything I did to the motor. Any suggestions are appreciated!

XR's only bored/honed the cylinder to 100.5mm New JE 100.5 piston installed with Honda rings from am XL600 (100mm) .5 oversize. Head soda blasted, new Kibblewhite valves, 3 angle valve job, new rocker arms, new cam, new valve springs

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Scouring on the Piston..Doesn't sound good. I spent mega bucks trying to solve a smoking problem..Bad rebore and shoddy workmanship means I had to get everything done twice..Scouring--Smoke.

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Xr's Only used to sell them, I think they were only made for them. It is hand engraved Xr's Only XR600 100.5. I'm pretty sure I bought the last one and they didn't have the matching ring set so they sent Honda rings. I know the scouring on the skirt isn't the greatest thing, but since it was smoking before I ever had it in the sand, I wouldn't think that would be the cause. The cylinder wall doesn't have any grooves I can feel on the scoured side, just some dark lines. I was thinking I should take the cylinder to a local machine shop and have it meausured to check Xr's Only's work.

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Even if you hadn't done the seals I wouldn't expect them to leak. I've got 30 year old engines that still don't smoke. Check the bore for out of round. Could ring end gaps be wrong or all lined up? Check guide to stem clearance. Check for a head gasket that didn't seal properly. Check the carb isn't flooding so badly as to wash the cylinder and score the piston from no oil film. Good Luck.

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