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Intermittent Miss and Sudden High Oil Consumption

Steve Pierce

BENEFACTOR
Graham, TX
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/technical_publications/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 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.
 
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
 
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/technical_publications/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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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!
 
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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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
 
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
 
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
 
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
 
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.
 
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.
 
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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