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Thread: Intermittent Miss and Sudden High Oil Consumption

  1. #1
    Steve Pierce's Avatar
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    Intermittent Miss and Sudden High Oil Consumption

    Was following a Carbon Cub cross country flight on Facebook that was having some engine issues. Was first identified as contaminated fuel system but further flight proved that might not have been the cause. Oil consumption went up rapidly and the engine would miss intermittently. Luckily it was an easy fix. The crankcase vent terminates into the 4 into 1 exhaust pipe and needs to be cleaned out periodically with a round brush. Cub Crafters issued a service instruction on the subject. If you fly a Carbon Cub this is a good one to be familiar with.

    http://legacy.cubcrafters.com/techni...ations/74/view

    Cub Crafters has a lot of service documents on their website which makes maintaining these airplanes way easier.
    http://cubcrafters.com/service-support/publications
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
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  2. #2
    spinner2's Avatar
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    I like the CC exhaust system but it does have this issue. This venting into the collector keeps the belly very clean.

    Mine me got replaced with a Vetterman crossover system quite a while ago and I really like it.
    "Fast is fine, but accuracy is everything." Wyatt Earp

  3. #3
    Farmboy's Avatar
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    Steve,

    So the vent gets plugged, increasing case pressure and causing oil burn rate to increase. What causes the miss, the oil burn?

    thanks,
    pb
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  4. #4

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    Quote Originally Posted by Steve Pierce View Post
    Was following a Carbon Cub cross country flight on Facebook that was having some engine issues. Was first identified as contaminated fuel system but further flight proved that might not have been the cause. Oil consumption went up rapidly and the engine would miss intermittently. Luckily it was an easy fix. The crankcase vent terminates into the 4 into 1 exhaust pipe and needs to be cleaned out periodically with a round brush. Cub Crafters issued a service instruction on the subject. If you fly a Carbon Cub this is a good one to be familiar with.

    http://legacy.cubcrafters.com/techni...ations/74/view

    Cub Crafters has a lot of service documents on their website which makes maintaining these airplanes way easier.
    http://cubcrafters.com/service-support/publications
    I use a rifle cleaning rod with a .45cal bore brush. Punch the bore with every oil change.


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  5. #5
    cubdriver2's Avatar
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    Quote Originally Posted by Farmboy View Post
    Steve,

    So the vent gets plugged, increasing case pressure and causing oil burn rate to increase.

    thanks,
    pb
    Even quicker if you have a smoke system

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  6. #6

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    That is good info.

    Just the normal crankcase breather needs cleaning once in a while. What is in there looks a lot like what an abandoned outhouse looks like - or a jet outflow valve back in the smoking days!

  7. #7
    Scouter's Avatar
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    Upon the advice of Mr Pierce-of the Texas Pierces, I stuck my head anda flashlight in he exaust stack of Mr CarbonCub
    Crank vent tube was nearly closed off with carbon crap
    Excellent advice. Thx
    jim
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  8. #8
    www.SkupTech.com mike mcs repair's Avatar
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    guess you won't have a frozen breather....either...

  9. #9
    mvivion's Avatar
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    I think if it were me, I’d rearrange that breather setup. Seems like a problem waiting to happen. Stick the end of the breather in a bottle if you can’t stand a bit of oil on the belly.

    MTV
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  10. #10

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    It should still have a whistle slot in the tube, even when vented to exhaust. I saw a CC recently at Valdez and was wondering why I did not see one.
    DENNY

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    Venting exhaust into the intake is a old hot rod trick. It is supposed to seal the rings better by using venturi effect to add suction to crankcase. Lucky he did not blow front seal.
    DENNY

  12. #12
    Steve Pierce's Avatar
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    Works very well. Simple procedure at oil change and can be cleaned with the cowl on. Just needs to be done.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
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  13. #13

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    We used one way check valve at header collector.Valve was from the AIR system (smog pump).It prevents reversion backflow into breather line.
    KB

  14. #14
    PerryB's Avatar
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    I don't think reversion is an issue. The line is getting plugged due to coking and the engine can't get rid of it's own blow-by.
    After Monday and Tuesday, even the calendar says WTF !

  15. #15
    cubdriver2's Avatar
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    Quote Originally Posted by willyb View Post
    We used one way check valve at header collector.Valve was from the AIR system (smog pump).It prevents reversion backflow into breather line.
    KB
    A PCV valve?

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  16. #16
    PerryB's Avatar
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    He's talking about a check valve like you'd find on the air injection hose (smog pump hose) between the air pump and the exhaust manifold on a 70's - 80's era vehicle. Usually about a 3/4" line.
    After Monday and Tuesday, even the calendar says WTF !

  17. #17

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    Steve P is a true lifesaver.

    I did have a gas contamination issue which caused the initial rough running situation.

    Timing just worked out that I also had the clogged vent.

    So grateful for the SuperCub community to get me back in the air. Steve (SuperCub.org) and Steve P, I cannot thank you enough.


    Here’s the video log I made of the trip. I’ll further explain in a future release. (Doing these videos takes a little time!!)

    https://goo.gl/F3uo5u

    ~ Cory Robin



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