Oil in Air Filter


Old 04-26-09, 07:14 AM
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Join Date: Apr 2009
Location: Michigan
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Oil in Air Filter

I have a Gravely rider with a Briggs 16hp Vanguard OHV M/N 303777 Type 1142-E1. I recently purchased this mower from my neighber who used it about three seasons. The last time it was used the engine suddenly started to idle rough and it appeared to be burning oil. The mower sat for about three years before I purchased it. I drained the old gas, replaced the fuel filter and charged the battery and the engine started up with no problem. What I have noticed is the engine runs fine until it warms up and is under a load (blades engaged). This is when it starts to smoke and idle rough. I pulled the air filter off and noticed oil was present. I have read on other threads it could be the head gasket. How can I check for a bad head gasket. I have read conflicting opinions on doing a compression check.

Any help would be appreciated,
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Old 04-26-09, 08:09 AM
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The compression check will tell you if you have a problem with the head gasket, rings, or the valves. Since it runs Ok then acts up, you could rule out the rings and valves. The oil in the breather is a good sign of too much crankcase pressure or an overfill of oil; or an overly high level of oil in the crankcase because of a leaking carb which funnels gasoline into the crankcase = overfill.

The conflicting posts here that I have seen have to do with the adding of oil to the cylinder to determine ring/cylinder wear. If you only add an ounce of oil (like 10w40) to the cylinder of a lawnmower engine (four stroke), then turn the engine over maybe five times, the oil will distribute itself into the piston gap in the cylinder and seal the rings temporarily.

That sealing at the rings will jump the compression significantly and will point to the ring/cylinder seal as being the problem.

That method of compression testing has been around for the last forty years that I'm aware of and it always worked.

In your case, in my opinion, if the oil level in your engine is right and you don't have it diluted with gasoline, I would just replace the head gaskets if you can do the work yourself. If not I'd get a tester and check the compression.
Old 04-26-09, 08:50 AM
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Join Date: Apr 2009
Location: Michigan
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Oil in Air Filter

Thanks for your advice.

Checked the oil and it was right at the full mark. When I drained the oil it did not appear diluted with gas but was very dark.

I am an engineer and have a fair amount of automotive knowledge, but the days of working on small engines goes way back.

I think Ill look for a manual for this engine and look into replacing the head gaskets. If I do a compression check what what would you expect for a reading?
Old 04-27-09, 12:45 AM
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A leakdown test would give you more information. A good compression reading would be over 90 psi, preferrably 110-130.
Old 05-04-09, 05:42 PM
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Join Date: Apr 2009
Location: Michigan
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Thanks Cheese and Marbobj.

Sorry for the late update but finally got time to change the head gaskets. Fixed, runs like new. Torqued everything to spec, no more oil in carb.

I just mowed 2.5 acres of grass with no problems.

Thanks again,

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