Cylinder compressions low on an IO-360

Discussion in 'Maintenance Bay' started by arnoha, Jan 4, 2019.

  1. arnoha

    arnoha Cleared for Takeoff

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    More bad news...I was just informed that, during a 100-hour, the IO-360-L2A in my 172S read 20/80 on cylinders 1 and 2. The kicker? Cylinder #1 was replaced in February, about 300 hours ago, due to reading nearly no compression. #2 is likely from the overhaul, 1200 hours ago. The shop is evaluating right now, but I'm curious what could be causing repeated failures like this? What sorts of questions should I be asking? This is very frustrating...the parallel valve IO-360 is supposed to be bulletproof.

    EDIT: Another thing I should note, since this plane is a leaseback, it gets 100 hour inspections. At the last 100 hour, compressions were fine. Need to go figure out exactly how high, but it was high enough that no concern at all was noted, so I'm assuming over 65/80. Whatever happened, it didn't give any warning. Oil analysis was also clean.
     
    Last edited: Jan 4, 2019
  2. Clip4

    Clip4 En-Route

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    My suspicion is pilots are not leaning properly. Did cylinder 1 in February have a burnt exhaust valve?
     
  3. PaulS

    PaulS Final Approach

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    Was the engine warm? My opinion is that quality control on these cylinders is not what it should be.
     
  4. arnoha

    arnoha Cleared for Takeoff

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    I don't believe so...I would have remembered that. I'll ask. Interesting note: they recommended replacing the cylinder last time, but are only recommending honing and rings this time. I've sent an email asking why.

    Leaning is probably a mess, yeah. It's a leaseback and a classic training plane, so I assume the red knob is being used poorly when anyone bothers to touch it at all.
     
  5. arnoha

    arnoha Cleared for Takeoff

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    They did the compression both cold and warm. Warm did not improve matters. Also, cylinder #1 was replaced with overhauled in Februrary, not new. I figured with only 1000 hours left to TBO, it should make it that far. Guess I was wrong.
     
  6. MooneyDriver78

    MooneyDriver78 Pattern Altitude

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    Borescope it.


    Tom
     
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  7. Kenny Phillips

    Kenny Phillips Pattern Altitude

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    As they did a leakdown test, they should have instantly known whether the issue is intake or exhaust valve, or piston rings/cylinder.
     
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  8. Checkout_my_Six

    Checkout_my_Six Final Approach

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    Dirty/clogged injector will cause those cylinders to run hot at full power. Is there an engine analyzer?
     
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  9. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Yep,,,, that's where I'd start.
     
  10. Stewartb

    Stewartb Final Approach

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  11. arnoha

    arnoha Cleared for Takeoff

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    This is all great information. Haven't seen an email today and shop would be closed at this point. I'm unsure if the chief mechanic will be working tomorrow, and this is serious enough that it would be worked by him. Might have to wait till Monday to get more info. I'll fire off an email with some of these questions.
     
  12. arnoha

    arnoha Cleared for Takeoff

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    No engine monitor. Still has only the stock engine equipment...single point EGT, oil temp, oil pressure, fuel flow (that's really fuel pressure). No CHT, no per-cylinder EGT, no flow transducer. I've debated putting a monitor in. Everyone I've spoken to says it's pricey overkill for a 172 and that it'll just confuse the students. I'm beginning to think that may be bad advice.

    Side note on the injectors...I did have an injector fail (literally fall apart in the mechanic's hands as he removed it) almost as soon as I bought it three years ago. Don't remember which cylinder it was; I don't have the logbooks with me. Maybe that portends other injector problems. Maybe this is a good time to get GAMIs.
     
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  13. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Ahhh --- Yeah. this is why they were invented.
     
  14. Clip4

    Clip4 En-Route

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    Actually you are better off if they never lean vs leaning to aggressively or failing to enrich when when adding full power.
     
  15. Silvaire

    Silvaire En-Route

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    Then what? Nobody is going to poke a scope in there and say yea, it looks fine then sign it off. If it's got a 20/80 compression reading it's coming off regardless of what you think you see with a scope.
     
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  16. MooneyDriver78

    MooneyDriver78 Pattern Altitude

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    I would check cylinder walls for scoring, valves for proper seating, etc. I would do this after you do the leak down check of course.
    Maybe there is lead build up on the valves preventing proper seating, maybe you have a broken piston ring(s).


    Tom
     
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  17. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Well maybe not, really depends upon what we can do to prevent pulling it, rope trick may cure it for a little while. Flooding the cylinder with oil on compression stroke to see if we can loosen a stuck ring.
    Really you must do the trouble shooting prior to panicking and removing the cylinder.
     
  18. aftCG

    aftCG Pre-takeoff checklist

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    So you're saying that a leaseback may not be for everyone?
     
  19. Bell206

    Bell206 Pattern Altitude

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    Or the old drop-the-valve-into-the-cylinder and clean or ream trick.
     
  20. JOhnH

    JOhnH Touchdown! Greaser! PoA Supporter

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    The fact that it is a leaseback does negate "some" of the reasons for getting a engine analyzer, but not all of them But this is a good example of why an analyzer is so important if you can be sure the pilot will use it.

    But even in a leaseback, you can download the data and see what has been going on. This can give important information, and hopefully, the CFIs will have a clue about using it properly.
     
  21. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    takes a rope to do that. thus the rope trick
     
  22. AKBill

    AKBill Pattern Altitude

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    Don't think I would ever do a lease back. I abuse the plane enough myself, but at lease I know what I did. A renter is not going to say squat about how they ran the plane.

    A lot of good points have been made.

    As stated I would look at injectors also if engine was started with out preheating in cold weather. Type of oil may make a difference. I'm flying between 50 to 75 hours a year (wish I could fly more, work and weather makes it hard). I have used Phillips Type M oil for the last few years with good results. I have a filter installed 2 years ago and change every 25 hours. Works for me.

    Good luck, hope you find out what the problem is..
     
    Last edited: Jan 5, 2019
  23. CC268

    CC268 Final Approach

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    Gotta use full rental power lol
     
  24. asicer

    asicer En-Route

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    Can't speak to the first part, but as for the second part the G1000 has a built-in monitor/analyzer and primary students don't seem to be too confused by it.
     
  25. Jamie Kirk

    Jamie Kirk Pre-takeoff checklist

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    The term fly it like it’s rented comes to mind.
     
  26. Bell206

    Bell206 Pattern Altitude

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    I guess it depends how it was done. The guy that showed me used the rope first and if that didn't break the valve loose, he pulled the rope, then pulled the keepers, tied dental tape to the stem, pushed the valve in and went about his business cleaning.
     
  27. arnoha

    arnoha Cleared for Takeoff

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    Leaseback is definitely not for everyone. It makes sense for me (even with this), but it really depends on the right combination of club, plane, and location. And luck. Definitely luck is involved.

    I've also learned that, for leaseback, you need a deep reserve, significantly deeper than for private ownership. It's cheaper in the long-term (I've done the math). But in the short term, it can really hurt you.

    No news yet...I'll go in and chat directly on Monday.
     
  28. Silvaire

    Silvaire En-Route

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    Maybe if you're stuck out in the boonies somewhere but in a hangar full of tools I'm just gonna pull the jug off and fix it right.
     
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  29. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    THat's what I'm saying, find it early, fix it right and add life to the cylinder/engine. and stop the worries about breaking down across country
     
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  30. Bell206

    Bell206 Pattern Altitude

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    I'm with you on that. Fortunately or unfortunately, was never in a situation where a cylinder was half broke. Every one I pulled was to verify the damage: popped valve seat, burnt valve, cracked head, missing pieces, etc. The guy that showed me the valve/cylinder trick took care of a number of crop dusters. He could do more things on a complete installed engine than anyone else I knew. But it was always good to know the tricks if I ever was stuck in the boonies. Not that it matters anymore.
     
  31. arnoha

    arnoha Cleared for Takeoff

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    Fortunately for me, it was caught during 100-hour, at the home airport, in the club MX hangar, so there's no need for jury-rigged tricks on this cylinder failure.
     
  32. arnoha

    arnoha Cleared for Takeoff

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    New information today...he did an abbreviated compression test with me there, and you could definitely hear the leak into the crankcase. And I'm mostly deaf. 1 and 2 were in the 10-20/80 range, though we were doing the test cold. The rear two were over 70/80.

    He's pulling the jugs and sending them out. Honing and rings are the likely result. It'll be interesting to see what the inside of the jugs look like.
     
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  33. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Dropping a valve into the cylinder then pulling the stem out thru a spark plug hole and cleaning it isn't what I'd call a "Jury Rig". It simply cleans away the hard carbon that will eventually ruin the guide.
    In fact I did one today on a Maule MX-7 /180..or should I say I coached the owner thru the evolution. The compression on the cylinder was 40/80 cold, after the compression was 76/80 cold.
    The owner called me because the A&P wanted to pull the cylinder, and send it out to be re-built.
    Fixing a cylinder in place is always better. These routines have been used for many many years. They work.
     
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  34. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    There isn't anything you can do with bad rings/pistons but pull the cylinder.
    Show us pictures.
     
  35. simtech

    simtech En-Route PoA Supporter

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    If I'm not mistaken this is a lycoming service bulletin no?

    How long does it typically take to do it? Just reading through the SB on the wobble test seems kind of involved and time consuming needing special tools.
     
  36. Salty

    Salty En-Route PoA Supporter

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    Why?
     
  37. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    cost,
     
  38. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    You do need the base plate, and a dial indicator. shouldn't be much over an hour.
     
  39. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    This test is to determine the amount of wear in the guide, too much wear and the valve will not set square on the seat and thus leak.

    this test can't be true if the valve stem isn't clean.
     
  40. Salty

    Salty En-Route PoA Supporter

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    At the risk of causing further damage and increasing cost, or having to pull the cylinder anyway meaning paying for the “don’t pull it repair” in addition to the real repair.