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Thread: Oil leak somewhere near the carb

  1. #1

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    Oil leak somewhere near the carb

    I thought I was losing oil from the hose sections on the oil return lines. Turns out those leaks are minor. After cleaning the lower cowling, it's obvious that the oil is leaking somewhere around the carburetor.
    I lose about a quart an hour so it really need fixing.
    No leak when sitting, only when the engine is running. Bolts all seem tight. O320B2B.
    Suggestions?

  2. #2
    skywagon8a's Avatar
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    There is no place around the carburetor which would leak with the engine running and not leak when the engine is stopped. Thoroughly clean the bottom of the engine with some solvent. Fly the plane once around the traffic pattern and look for the leak. Look inside the ring gear behind the alternator belt groove. If the nose seal is leaking that will be wet along with the seam of the case just behind it.

    Sometimes, particularly in cold regions like yours if there is no vent in the crankcase breather tube (whistle opening) in a warm location, the breather tube can freeze over causing a pressure build up inside the crankcase. This condition can push out a nose seal if the adhesive has loosened. This will spit out oil sometime in quantity. If the adhesive is weak the seal can slide out on it's own.

    Alternatively check the clamps and connector hoses for the rocker box drain tubes where they enter the crankcase. Maybe one of the connector hoses is broken? Check these first.
    N1PA
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  3. #3

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    I’ve seen leaks at the filler tube quite often. Best way to find a leak is to clean the engine very good, dry it, and put baby powder all over any area of suspected leaks. Run for 5 minutes and check. Repeat until you have signs of oil in the baby powder. Once the baby powder shows oil, you found at least one leak!

    Have you looked at your oil cooler? If you have the nose cooler, and it’s leaking, it could be blowing back on the engine.


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  4. #4
    www.SkupTech.com mike mcs repair's Avatar
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    Dga hit the baby powder trick. Also look look up top at Push rod housings... just because it drips off at the bottom doesn’t mean that’s where it came from. Also check cylinder base nuts


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  5. #5
    skywagon8a's Avatar
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    Quote Originally Posted by dgapilot View Post
    I’ve seen leaks at the filler tube quite often.
    Not at the rate of a quart an hour.
    N1PA

  6. #6
    Steve Pierce's Avatar
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    The bottom of the crankcase halves forward of the carburetor is notorious for leaking. Removed bolts, clean, put Aviation Permatex in holes and on bolts, retorque and hold your mouth just right.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
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  7. #7

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    Quote Originally Posted by NunavutPA-12 View Post
    I thought I was losing oil from the hose sections on the oil return lines. Turns out those leaks are minor. After cleaning the lower cowling, it's obvious that the oil is leaking somewhere around the carburetor.
    I lose about a quart an hour so it really need fixing.
    No leak when sitting, only when the engine is running. Bolts all seem tight. O320B2B.
    Suggestions?
    When I had my Howard, the R985 wouldn’t even go through a quart an hour!


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  8. #8
    cubpilot2's Avatar
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    I've seen crankshaft nose seals do weird things depending on the airflow through the cowling.
    Friend of mine had what he thought was for sure an oil cooler leak but turned out to be the seal.
    Perhaps the airflow is drifting oil to the front of the sump....

    The baby powder trick works awesome. I've used it for years.
    Ed

  9. #9
    supercrow's Avatar
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    I suspect like Steve that the case is fretting and leaking at the case split. Around the starter mount is a common place for a crack and leak too.
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  10. #10

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    Here's some photos. The sides of the lower crankcase and the sump are fairly dry. There is some oil on the lower left side of the engine mount. I tightened up all the case-half bolts and those holding the sump in place. Mag bolts and accessory case bolts are all tight. I'm now losing about 1/2 qt. in a 1.5 hour flight. Leaks only when running.
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  11. #11

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    Big oil leak!! Flying along 10 miles South Cascade, Idaho this morning, minding my own business.
    Glanced over at gauges and 0 oil pressure! Trottl3d way back and headed for Cascade. Copper oil pressure line broke. Didn't have much oil when I got to Cascade. Mike Arnold was there and fixed me up. Restector goes in that line.
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  12. #12
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by NunavutPA-12 View Post
    Here's some photos. The sides of the lower crankcase and the sump are fairly dry. There is some oil on the lower left side of the engine mount. I tightened up all the case-half bolts and those holding the sump in place. Mag bolts and accessory case bolts are all tight. I'm now losing about 1/2 qt. in a 1.5 hour flight. Leaks only when running.
    Click image for larger version. 

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    Need more pictures. Oil screen? Housing ears bent and or cracked?


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  13. #13

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    I have noticed a decline in the leak recently. Down to 1/2 qt. in a 1.5 hour flight, and about 1/4 qt. if I keep the oil level at 5-1/2 qt.

  14. #14
    skywagon8a's Avatar
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    Larry, what is the condition of the gasket where the dip stick tube screws into the case? Those gaskets are generally just a thin paper materiel which can shrink causing leaks. A high oil level could work it's way out there getting blown forward fooling you into looking elsewhere. The paper gasket could be replaced with an "O" ring. It's not uncommon to find these tubes loose.
    N1PA
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  15. #15

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    I'll check that later today. Thanks Pete. The dipstick tube and the quick-drain fitting are two things I haven't checked for tightness yet.

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