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Thread: Compression Drop

  1. #1
    Senior Member Paul's Avatar
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    Default Compression Drop

    Hey guys, I'd appreciate any feedback or suggestions on a recent drop in compression on two (even) cylinders.
    Some background:
    I have 280 hours on my CCEX. (flying since January 2015)
    Compressions at time of last annual, this past spring, at 215 hours were great 78/79/78/78
    I always lean out, while taxiing and flying.
    Temps have always been super stable....Oil around 155 to 160, CHT's around 360 to 380, EGT's around 1000 to 1200
    Oil changes have varied between 25 hours and 35 hours.

    So here's the current situation...
    Changed the oil this week after 35 hours and it came out super black.
    Checked compression and I have two cylinders in around 67.
    Other two cylinders are 77/78
    Escaping air is coming from exhaust.
    Pulled valve covers and A&P working with me observed what he thought is some carbon buildup on the exhaust valves.
    cylinder walls look great
    no metal in the oil or oil filter

    So my questions for the forum...
    1) Does this all add up to the same conclusion for you....that the drop in compression is due to blowby on the exhaust valves?
    2) Is it possible the problem is the push rod clearance that needs adjusting (as suggested in the 340 Engine Problem thread) ?
    3) If there is carbon deposits on the exhaust valves why would they appear so suddenly? (my oil was not this black on the last oil change)
    4) Why carbon deposits only on two cylinders?
    5) What do you suggest I could do to get rid of the carbon deposits if that's indeed what the problem is?

    Thank you,
    Paul
    Last edited by Paul; 11-18-2016 at 08:09 AM. Reason: Just adding some detail

  2. #2
    Senior Member ceslaw's Avatar
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    Default Re: Compression Drop

    I have been told that the blow by passes through a small opening in the collector which can become clogged and must be cleared from time to time. A welding rod with a hook bent on the end can be inserted in the exhaust pipe to clear away any carbon build up in that opening.

    I have not yet had occasion to address this issue, so this information comes second hand.

    But I wonder if blockage of your blow within the collector could have led to this sudden problem

    Chuck

  3. #3
    Senior Member Paul's Avatar
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    Default Re: Compression Drop

    That could be Chuck. Thanks. Although I did clean it thoroughly this past annual about 70 hours ago.

  4. #4
    Senior Member TroyBranch's Avatar
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    Default Re: Compression Drop

    I dought the breather tube would be the issue. But always make sure it is clear. When your engine does not drip on the floor, the tube is likely plugged. Sounds like you are running very rich and the oil temps are to low.

    In cruise you should see EGT's on the high 1300 to low 1400 depending on power setting if leaned right. Get that oil temp up to 180 min. to 200. I have my cooler half blocked off in summer and it will be almost closed off comes winter up here.

    What do your plugs look like?

    I am not an engine expert but the carbon on the valves are likely because of the lack of leaning?

  5. #5
    Senior Member Paul's Avatar
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    Default Re: Compression Drop

    Plugs looked good Troy. Definitely not fouled or showing any deposits. But no question I'm not running that hot on my EGT or oil temp. Ok, I'll start by covering half my oil cooler and leaning more aggressively. Thx
    Last edited by Paul; 11-18-2016 at 08:15 AM.

  6. #6
    Senior Member TroyBranch's Avatar
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    Default Re: Compression Drop

    Even with all the fancy EFIS stuff to nail the leaning numbers, lean until just rough and richen until smooth will set the engine at an LOP operation with your eyes closed. Well don't close your eyes, but you know what I mean.

  7. #7
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    Default Re: Compression Drop

    Quote Originally Posted by TroyBranch View Post
    Even with all the fancy EFIS stuff to nail the leaning numbers, lean until just rough and richen until smooth will set the engine at an LOP operation with your eyes closed. Well don't close your eyes, but you know what I mean.
    Good Info here on proper leaning. Us old school pilots always learned to lean 50 deg rich of peak and it's seems that was all wrong. Stay on the lean side of peak for much better performance. Check this out from Mike Busch about the Embry-Riddle example.

    http://www.eaavideo.org/video.aspx?v=2274677932001

  8. #8
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    Default Re: Compression Drop

    Quote Originally Posted by Paul View Post
    Hey guys, I'd appreciate any feedback or suggestions on a recent drop in compression on two (even) cylinders.
    Some background:
    I have 280 hours on my CCEX. (flying since January 2015)
    Compressions at time of last annual, this past spring, at 215 hours were great 78/79/78/78
    I always lean out, while taxiing and flying.
    Temps have always been super stable....Oil around 155 to 160, CHT's around 360 to 380, EGT's around 1000 to 1200
    Oil changes have varied between 25 hours and 35 hours.

    So here's the current situation...
    Changed the oil this week after 35 hours and it came out super black.
    Checked compression and I have two cylinders in around 67.
    Other two cylinders are 77/78
    Escaping air is coming from exhaust.
    Pulled valve covers and A&P working with me observed what he thought is some carbon buildup on the exhaust valves.
    cylinder walls look great
    no metal in the oil or oil filter

    So my questions for the forum...
    1) Does this all add up to the same conclusion for you....that the drop in compression is due to blowby on the exhaust valves?
    2) Is it possible the problem is the push rod clearance that needs adjusting (as suggested in the 340 Engine Problem thread) ?
    3) If there is carbon deposits on the exhaust valves why would they appear so suddenly? (my oil was not this black on the last oil change)
    4) Why carbon deposits only on two cylinders?
    5) What do you suggest I could do to get rid of the carbon deposits if that's indeed what the problem is?

    Thank you,
    Paul

    Hey Paul,

    Think I sent you and email a while back but maybe you did not get it... I built a CC and finished it in May. Have 380 hours on it now...

    As far as EGT temps, the number does not tell much because it depends on where you put the probes and all engines are a little different. What would help is to know how many degrees rich of peak are you running normally and at what power setting.

    My guess is that you are getting carbon on the valves and guides due to running to rich. When under 55-60 % power you can't hurt that engine with the mixture, so lean until you notice a loss of power and push it back it just a little bit until you get the power back. At the power settings I an most people use in this plane I just run it at peak EGT all the time. I question running LOP with this engine because when you do you are only running 2 jugs LOP the other 2 are ROP, I don't ike the CHT difference when this happens, on my fast plane I run LOP a bunch, but it is injected.

    Do what you have to do to get your oil up to 190-200 at least once a month. The oil cooler is WAY overbuilt. You need to get the oil above the boiling temp of water to get the moisture out... Tape your cooler 80% go fly get it hot and land. Open the dip stick and watch all the moisture come out.

    You may need a valve job on the 2 jugs, or it could just be a chuck of carbon not allowing the E-valve to close all the way.

    Good luck...

    Jason Sneed
    EX-2

  9. #9
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    Default Re: Compression Drop

    Quote Originally Posted by kemper28 View Post
    Hey Paul,

    Think I sent you and email a while back but maybe you did not get it... I built a CC and finished it in May. Have 380 hours on it now...

    As far as EGT temps, the number does not tell much because it depends on where you put the probes and all engines are a little different. What would help is to know how many degrees rich of peak are you running normally and at what power setting.

    My guess is that you are getting carbon on the valves and guides due to running to rich. When under 55-60 % power you can't hurt that engine with the mixture, so lean until you notice a loss of power and push it back it just a little bit until you get the power back. At the power settings I an most people use in this plane I just run it at peak EGT all the time. I question running LOP with this engine because when you do you are only running 2 jugs LOP the other 2 are ROP, I don't ike the CHT difference when this happens, on my fast plane I run LOP a bunch, but it is injected.

    Do what you have to do to get your oil up to 190-200 at least once a month. The oil cooler is WAY overbuilt. You need to get the oil above the boiling temp of water to get the moisture out... Tape your cooler 80% go fly get it hot and land. Open the dip stick and watch all the moisture come out.

    You may need a valve job on the 2 jugs, or it could just be a chuck of carbon not allowing the E-valve to close all the way.

    Good luck...

    Jason Sneed
    EX-2
    Hi Jason,

    What do you mean about when you run LOP that 2 cylinders will be LOP and 2 ROP?

  10. #10
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    Default Re: Compression Drop

    Quote Originally Posted by Daveembry View Post
    Hi Jason,

    What do you mean about when you run LOP that 2 cylinders will be LOP and 2 ROP?

    Not sure what you are asking but I'll say it a different way...

    When you lean and watch your EGTs, at some point the hottest egt will start to go down, at this point you are lean of peak on that jug, At this point the other 2 or 3 jugs will still be at either rich of peak or peak.

    If you run the engine this way, some of your jugs are lean of peak and some are rich of peak. Personally I do not like that because you will have one jug at say 390 CHT and the lean of peak jug will be at say 300 CHT.

    Now, hot to run an engine is highly debated.. And I am by no means an expert.

    Bobby loper (forgot how to spell his last name) is the guy at centennial for this engine. He was around for the design and testing, there is a good chance he built your engine or at least signed off on it. At any rate, he says do not run it lean of peak for the reasons I said above.

    Lots of guys at cub crafters do run LOP and even recommend it...

    For me low power setting 2150 or so, and peak EGT is the best. When you really analyze the difference between 2150 at peak and say 2200 LOP the fuel savings amounts to basically nothing... Maybe save $200 during the life of the engine.

    The power setting I use above burns 5.6 gallons an hour, which is my FF in cruise 90% of the time.

    Sorry is you knew all this stuff already,

    Jason

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