Small Engines (Lawn Mowers, etc.): Onan crankcase breather blowing oil, crankcase breather, piston ring

Question
Onan B43M GA016 (intake #170-2968).  Engine seems to run strong and smooth until the air cleaner box gets saturated with oil spitting up through the two crankcase breather hoses.  One breather hose comes through 5/16"?? hose from the top of the block.  Second is a 1.5"?? hose tapering down to 3/8"?? at the air cleaner.  It comes from the valve cover/breather.  The force of the hot air/oil mix being blown is very strong.  I plugged the larger hose to see what would happen and it just blew off the other end.  What do you recommend I check next?


Answer
Possible causes:

  1. Too much oil in crankcase.
  2. Engine speed is excessive.
  3. Oil fill cap or gasket is damaged or missing.
  4. Breather mechanism is dirty or defective.
  5. Piston ring gaps are aligned.
  6. Piston rings are worn.