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post #1 of 5 Old 11-27-2009 Thread Starter
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Crankcase overfull

In August, on a Gulf of Maine transit to Nova Scotia, running @ 2800 RPM, we had knocking & blue/white smoke in a couple of incidents that were first suspected of air in the lines. We tightened up the fuel lines, replaced some banjo washers, and had repeat incidents on the same and subsequent days. First time was after running ~2 hours. Then subsequent was ~an hour later. If we ran at 2200 on the level it was OK. Motorsailing @ 2100 heeled a little in 5k breeze would knock & smoke.

Later investigation found the crankcase with an extra 1.25 qts of oil in a 2.75 qt. capacity which was pulled out ounce by ounce with a turkey basting syringe from a hardware store. The symptoms fit with Calder's troubleshooting guide as an overfull crankcase. The balance of the trip proceeded holding the oil level. Looking at last year's yard bill, they had put in a gallon instead of 2.75 qts., so I'm pretty confident that it was not fuel washdown.

So, a couple of questions.
What was happening? I can see from the engine crossection that this amount of overfill would bring the level up, probably, to the bottom of the pistons. Most likely there was excess pressure building in the crankcase that then what? Forced oil up past the rings? Or just the backpressure under the pistons?
Damage likely? We ran back across the Gulf 2 weeks later on an unfortunately windless day/night @ 2800 for 21 hours purring like a kitten (knock on wood). Oil analysis came back good and close to values from two years ago.
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post #2 of 5 Old 11-27-2009
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You're probably OK. Overfilling results in the churning and foaming of the oil by the crank and piston rods and can result in poor lubrication due to the aerated oil. Doesn't sound like you did any damage.
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post #3 of 5 Old 12-01-2009
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The biggest danger with a seriously over-filled crank case is the possibilty that the breather can push oil spray into the manifold (depending of course upon the layout) and in rare cases the engine can "run away", being fueled uncontrollably by the by-passing oil.

You have clearly escaped that so I reckon you will have no damage.


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post #4 of 5 Old 12-01-2009
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I think the oil testing would have showed any fuel in the oil.

Always check you oil before you use the motor that way you will find problems early.

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post #5 of 5 Old 12-05-2009 Thread Starter
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yes the oil was checked pre-trip & even after first knocking but the dipstick setup is a little deceiving because that much overfull was only ~1/16 - 1/8" above the line which, at the time, seemed inconsequential
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