Motorcycle Repair: yamaha, crankcase breather, piston ring

Question
I have a older yamaha bike  i am getting oil into the air cleaner box the bike does not smoke like a busted ring ,thanks 4 your help

Answer
John, the specific model would have been helpful, but oil in the air box is coming from the crankcase breather tube. Oil solids will collect in the air box system when the engine is run hard, is overfilled with oil or is just getting tired.

Run a compression check to see how the cylinder pressure is, then look at the spark plugs you removed to do the test and see what they look like. If they are pretty clean and not caked with burnt oil solids, then the oil accumulation may be somewhat normal for that bike and just needs to be cleaned periodically.

Hondas have a specific drain hose from the bottom of the air filter chamber to drain out oil build-up. A small amount is normal. Larger amounts accumulating regularly are signs of piston ring wear or they might have gotten stuck in the piston grooves from long storage or infrequent oil changes that caused varnish to form in the ring lands. This can cause the rings to stick in place, rather than expand/contract and you will develop some blow-by past the rings and pistons into the crankcase, which is expelled out the breather hose.

The mileage on the engine, size of engine and type of use all play into the bigger picture of what is normal and what is wearing out.

Bill Silver