I have a 2002 honda 400ex that is burning oil. The person i bought it from said they rebuilt the engine not to long ago. I asked if they replaced the the piston rings and they said yes. What else could cause the ATV to burn oil? Thanks for your help.

 

Was the cylinder measured for out of round and were the valve stems and guides measured ..

 

he said they bored it out, and he did not say anything about the valve stems. My second thought that it woulb be the valve seals? Any other ideas? Thanks

 

These are just a few off the top of my head.

Out of round bore.
Piston to bore clearance too big.
Ring end gap too big.
Wrong stone used on final pass of jug.
Piston worn beyond spec's.
Ring lands worn beyond spec's.
Wrong oil used for break-in.
Improper break-in.
Out of spec valve stems.
Out of spec guides.
Bad valve seals.

Maybe a half dozen more that I'm not thinking about right now.

 

I think you beat me to the post. I have an 06 400ex that I purchased from someone who did not know much about it's history. Anyway I have to add oil after every 2-4 hours. Anyone riding behind me says they smell oil burning but it does not smoke. It does not leak.. must be burning it. Not sure where to start, but I look at it this way I dont have to change oil so much, as I am always putting fresh oil in it.

 

My oil does not run out that fast, i rode it for 3 hours and only half the oil resevoir was empty. Any help is much appreciated. I will tear the engine apart later in the winter.