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It says you put new rings and valve seals. Says nothing about bore and hone. Did you have the cylinder spec'd out and honed before you put it back togeather? 99.999% of the time just slapping new rings in dosnt fix the actual problem. The cylinder needs an over bore in almost every case. Did you see cross hatching in the cylinder or did it look like a mirror?
 

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You would be 100% right but thermo expansion causes things to do weird things. Alot of forged pistons will actually slap and sometimes smoke alittle on start up until it expands to fit the cylinder. Your cylinder being a steel sleeve wrapped in aluminum for cooling purpose would make it expand very little but the piston being forged aluminum would expand at a very different rate. This is why piston clearances are very very important. A out of round cylinder can also cause similar issues. It says you put new valve seals in so as long as they were put in right you are down to very few possibilities. Valve guides(very very unlikely) or something to do with piston to cylinder clearance. My .02
 

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New piston rings require a fresh hone in the bore. Being able to see the original honed cross-hatch pattern in the bore doesn't count as having a fresh hone. :) You have to lightly hone the bore each time you replace the rings. Also important is the assembly... the rings have to be installed on the piston with the mark near the ends facing up. Ring gaps must fall within specs and those gaps need to be placed around the piston properly. If you are putting in a three-piece oil ring, special care must be taken assembling those correctly as well. I've seen those put together wrong many times...

Also, just for informational purposes... if the valve guides are worn out, installing new valve seals on those loose guides won't fix them.

There are too many factors that can contribute to your issue, so I won't attempt to hazard a guess.
 

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SlammedRanger explained some very good points. The bore has to be very good and straight and must have the proper fresh hone finish. The piston has to fit it very good. A used piston has wear on the skirts and thrust side of the crown. The ring lands are worn (and possibly hammered out a bit if the combustion chamber ever experienced any pre-ignition or detonation) so both new compression rings and the new oil ring will fit more loosely.

Sometimes the oil ring groove in the piston is found to be worn so much, that while assembling the oil ring one of the scraper rails (the top rail usually, because that one gets installed first) can get jammed in between the expander and the ring land, rather than on top of the expander where it belongs. I have seen many like that... extra care has to be taken when assembling a used piston. I don't mess around with used pistons... they are cheap so they get replaced along with the rings every time.
 
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