Onan P216 Blows oil

Discussion in 'Mechanic and Repair' started by 01duse, Sep 26, 2004.

  1. 01duse

    01duse LawnSite Member
    Messages: 5

    Good day, eh, from Canada. I am having some serious issues with the P216 Onan in my garden tractor and I was wondering if any of you could provide a little insight into my problem. It all started earlier this year when I mentioned to the local Onan shop that my engine seemed to lacking power. I was told to pull the heads and de-carbon the valvetrain, etc. I did as was suggested and also lapped and reset the valves to factory spec. Since then, the engine will blow so much oil/vapor out the vent tube that it accumulates in the air cleaner then spills out all over the engine. I pulled the valve covers several more times to ensure the vent was working and the valves were set properly but the problem seems to be getting progressively worse. This weekend as I was cutting grass, I pulled the dipstck and hot oil shot out like it had 20lbs pressure behind it. Yes, the vent is working properly....yes, the valves are set correctly....yes, there seems to be adequate compression(85lbs approx). The engines starts perfectly and runs/accellerates perfectly, but I cannot come up with a reason for the excessive crankcase pressure. I've never had one of these Onans apart before so I don't know if there is a pressure regulator screw on the oil pump or what all else is in there. Any bit of advice as to what to check or where would be greatly apprecited.Thanks.

    UNISCAPER LawnSite Bronze Member
    Messages: 1,426

    We run an Onan on our brick saw. From the sounds of things, compression is a tad low. You should be at 110-125lbs with no trouble at all.

    When ever someone tells me they "lapped" valves, that was a fix used way back when, the model T and A age. I'm not sure it was a figure of speach, or you actually lapped the valves by sticking compound in the seat and spinning the valves. If you did that, you may well have caused a gap between the valve and the seat unless you ground the stem to accomodate the lost materials from lapping.

    You are always best off to run new valves and grind the seats then check clearance.

    I would run a leak down test and check to see if, and where any air is passing to find the source of the oil consumption. Being that the Onan is opposed firing, all the valves are closer to the crankcase than a V or siamese engine, and, if any vaccum is produced in the case at all, the problems you describe become more noticable faster than the other designs.
  3. 01duse

    01duse LawnSite Member
    Messages: 5

    Thanks for the reply, uniscaper. I was wondering about the compression myself. I think I will pull the heads and check the valves and seats again. I will update in a day or two.
  4. allseasonturf

    allseasonturf LawnSite Member
    from ohio
    Messages: 15

    when an eng. builds crankcase pressure in excess of its "specs" its usually due to operater error. you removed the heads for the purpose of removing carbon and to lap the valves, Now depending on how much "lapping" you did, and if you polished the heads clean without cracking them,you very well could have miss alligned a head gasket or have blown one. In order for a crankcase to build this pressure it has to have access to incomming air. A blown head gasket will allow this. Way too often will someone remove heads and replace them with the old/used gaskets and not get a good seal.
  5. 01duse

    01duse LawnSite Member
    Messages: 5

    Thank you for the input, Allseasonturf. I was planning to pull the heads to check the valves anyway so pair of new gaskets will be in order. I guess I had falsely assumed that if the gasket was bad/leaking, then it would blow-by and vent to atmosphere, not back into the crankcase. I've been pulling my hair out on this one and any new ideas are appreciated. What are you thoughts on the compression? The Onan spec sheet says 75-115 as the range. Mine is sitting at 80-85 approx. Thanks again.
  6. tcruse2

    tcruse2 LawnSite Member
    Messages: 1

    :walking:it sounds like you may have compression leaking by the rings. if you have a valve problem it will miss or leak compression from the carb or exhaust, when it goes past the rings viola, crankcase pressure. hope you have good luck with the repair,

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