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Thread: O-340 low compression issues

  1. #1
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    Default O-340 low compression issues

    I have a 2010 Carboncub SS. Serial number 0126, 550 hours TTSN.

    At 350 hours cylinder #3 had low compression, 50/80. Turned out to be a burned exhaust valve. I pulled the cylinder and had it reworked by a good engine shop. It is doing great with 200 hours on it and has perfect compression. The cylinder was inspected, new exhaust valve, lightly honed and new rings installed.

    Now I have two other cylinders with low compression. 45/80. I never lean excessively, change the oil often and do not fly the plane hard. Fuel burn went up to 8.7 gph.

    This time the compression is leaking past the rings and very audible through the breather hose. Also the oil got very dark over the last few hours and oil was getting past the front crankshaft seal.

    I plan on pulling the 3 original cylinders and taking them to the same well known engine shop.

    Any thoughts or others with similar problems? Thanks

  2. #2
    Senior Member Dan L's Avatar
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    Default Re: O-340 low compression issues

    My first thought is a broken ring. Thatíll get new oil black quickly and cause other issues.

    Take a look here:
    https://forum.cubcrafters.com/showth...umption-Issues
    Flying Carbon Cub EX #11 since 2011

  3. #3
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    Default Re: O-340 low compression issues

    Quote Originally Posted by Dan L View Post
    My first thought is a broken ring. Thatíll get new oil black quickly and cause other issues.

    Take a look here:
    https://forum.cubcrafters.com/showth...umption-Issues

    Thanks for the link. The cylinders are off and no broken rings. The rings are worn (large end gaps) which I am sure caused to low compression. Also the rocker arm shafts were worn enough to require replacement. I am starting to question the quality control of the Titan engine parts. The engine has a full flow oil filter with oil changes at less than 50 hour intervals. It has always been run carefully and warmed up properly before takeoff.

    There must be others with the same problems??

  4. #4
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    Default Re: O-340 low compression issues

    Quote Originally Posted by GregJ View Post
    Thanks for the link. The cylinders are off and no broken rings. The rings are worn (large end gaps) which I am sure caused to low compression. Also the rocker arm shafts were worn enough to require replacement. I am starting to question the quality control of the Titan engine parts. The engine has a full flow oil filter with oil changes at less than 50 hour intervals. It has always been run carefully and warmed up properly before takeoff.

    There must be others with the same problems??
    How much dust do you get into? That will take out rings in a hurry. Do an oil analyses and check for high silicone.

  5. #5
    Senior Member Dan L's Avatar
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    Default Re: O-340 low compression issues

    Quote Originally Posted by GregJ View Post
    Thanks for the link. The cylinders are off and no broken rings. The rings are worn (large end gaps) which I am sure caused to low compression. Also the rocker arm shafts were worn enough to require replacement. I am starting to question the quality control of the Titan engine parts. The engine has a full flow oil filter with oil changes at less than 50 hour intervals. It has always been run carefully and warmed up properly before takeoff.

    There must be others with the same problems??
    I had all of my rocker arm shafts replaced by AeroSport when they went through the cylinders. They told me a couple of them were worn below limits. The new shafts are Superior.

    I replaced the pistons too. They were within limits but AeroSport gave me a good deal on new ones with the rings loaded and it made sense to start fresh. At the time the engine was getting close to 1000 hours on it. I have about 110 hours on it since the work was done and all is well so far.

    It seems all of the engine makers have problems with various parts at times.
    Flying Carbon Cub EX #11 since 2011

  6. #6
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    Default Re: O-340 low compression issues

    Quote Originally Posted by lbell View Post
    How much dust do you get into? That will take out rings in a hurry. Do an oil analyses and check for high silicone.
    Not much dust. Some off airport landings but most use is on paved strips. Air filter is changed often (not cleaned and re oiled). I will do an oil analyses after the new cylinders are broken in. Thanks for your thoughts.

  7. #7
    Administrator Pete D's Avatar
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    Default Re: O-340 low compression issues

    Quote Originally Posted by GregJ View Post
    and oil was getting past the front crankshaft seal.


    Any thoughts or others with similar problems? Thanks
    Is the crankcase breather in the exhaust clean? Should be cleaned every oil change. A brush like this makes it easy;
    https://store.cubcrafters.com/Hand-H...es_p_1995.html
    Pete Dougherty
    R & D Shop Manager
    Cub Crafters Inc

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