i have a 2002 450 foreman that starting smoking pretty bad seemed to clear up after it has been running for awhile, so i thought it was the valve seals i bought new valve took the head and found a puddle of oil on the top of the piston, cleaned it all out put the new valve seals in and still smoking bad. any ideas on what else this could be? motor starts first push of the button and runs great seems to have really good compression. if the rings were that bad wouldnt it make it hard to start? and also bad rings wouldnt make a puddle of oil on the top of the cylinder would it?

 

Did you inspect the value guide when you had head off? If guides are worn the value stem will move side to side an not let the seal work... Seal would leak....Try this.. Crank up atv an let run til the smokes clears up then park over night...In the morning take the carb. and exhaust off and look inside of head ports to see if either values is leaking or which is leaking...Would have oil on the back of value...If oily than you will know which one...If not thenvalues,guides,seals,head is okay then look further...Please let us know what you fine then we all will go from there..Good Luck..PS Yes rings and cylinder could be worn and still crank good if the values seats good...And egg shape cylinder could cause oil the get pump over to top of piston...But do the other test first to ease up our minds...! Were waiting to hear what you find out from this test..This test has worked great for me in the 40 years....

 

Ok tried what u said intake port looked clean, exhaust port was dark kinda oily. guess my next step is replacing the rings

 

Prolly miche bore first....May need re-bored...

 

When i had the head off the cylinder looked good still

 

If you want it not to smoke!!! Measure it!! Can't go by looks sorry on this one..An must to make sure...But It is your atv...Just an ideal tho.....Good Luck...

 

I just found out from the guy i bought it from he says it was bored out to a 500 im guessing if thats the case that would be to its limit?

 

Did you ever figure this out? I'm currently working on an exact 4 wheeler as yours with an identical problem, but on mine I noticed the washer below one of the valve springs hits the head on one end and can't seat properly. thanks