After Piston change smoking problem

[2qk4u]

I just installed a new 11:1 piston in my 2002 400ex. Bike runs awesome and everything went together fine. for some reason when the bike has set for a few hours and the engine has cooled down or the bike has set overnight, it wants to smoke when you first start it up, but after about 20-30 seconds of running it quits. it cant be the valve seals cause the bike id like new and didnt do this at all before the piston change. What I want to know is has this happened to anyone else before on there bike? do you think it will quit after more time has been put on the bike. i only have about 2 hours on it right now. All the rings were fine when installed. any help is appreciated.

[Ex'rMike]

Did you hone the cylinder before the new piston installation? Standard bore? New valve seals and or guides?
If you answer yes to all these, then I would put some more time on it before I tore back into it. Get back with me with some more info and I will see what I can tell you. Good Luck!
Michael

[dhines]

Oil smoke on startup is usually a valve issue. If the vavles aren't seating right or the seals are leaking, oil drips down into the cylinder and that is what you see when you start it up.

[MoparTrav]

What color is the smoke?

[quadman21]

I had the same problem. I had LRD do a 416 for me and when I put it back together it wouldn't stop smoking. It ran awsome just as you described but it still smoked. Come to find out the bore was out of round just enough to let oil by the rings. I had that fixed but then later on when I replaced my cam chain I replaced my rings because I already had it apart. It started to smoke again. I finally reallized that I did not have my ring gaps on my oil ring spaced properly. But I slso would give it a little while to see if it will clear up. That's just my sob story.

well, if u replaced ur piston and rings, ther will be oil in top end, it will burn out, dont worry, if it keeps smokin for a long time, check into it

[2qk4u]

well got my smoking problem fixed. had to take it back apart and found that the oil rings were really close together. got it back together and took it to the dunes yesterday and ran great. no more smoke on start up or anything.

[400exRacerX]

You meen compression rings??:huh

[2qk4u]

I mean oil rings.