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Thread: IO-520A pre-buy advice?

  1. #21

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    Jul 2011
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    Mike, as for the compression test, I have mine done when still warm, and I might see a variation of 10 lbs or so; but I would sure be surprised to find a 38lb test that did not indicate an actual problem,and was ok one flight later.
    If the exhaust valves are actually leaking I have found that you can hear the compressed air coming out of the exhaust pipe.
    In my case, I bought a 88 Be36 TC, with about 1200 hours, seemed to be in good shape. Frankly, since I had been flying a Mooney 201 for 10 years and it made it to TBO,and my T-34A had no real problems with the 0-470, I was not really aware and not as concerned with Cont engine problems as I might have been and my prebuy inspection may have missed something. The plane had already has one factory rebuilt engine for the previous owner due to case crack under warranty, so I sort of assumed the new engine to be good; and I also wanted the plane as equipped and as priced.
    I flew it for awhile, then on the way back from Sun n Fun, I noticed a rougher idle and loss of power on climb; still had good mag checks.
    When we got it home, one cylinder had NO, THAT IS ZERO, compression. Flying it another hour was not going to help; there was actually a pie shape piece missing out of the exhaust valve, just gone, so that I had about 315* of the original
    360* face. I had never seen something that bad. A couple of other ones were low but had some compression.
    The factory sold me some cylinders at cost. but I have still had some problems over the years, and had to buy a low time engine to replace that one due to a major case crack behind the alternator. By the way, my work back then was at an expert Beech shop, Pearce at Meadowlake.

    I didn't know that Cont factory cylinders had good and bad years. Thanks for the info. As for as I know, down there in Alabama, the teach real good football, but not so much readin n ritin or engine building.

    I may overhaul mine next year, am leaning toward Ram in Waco, and probably new ECI cylinders. I would appreciate your suggestion on this. Thanks

    PS my friend has their flight school Cirrus 22 down right now and engine at Firewall for a case crack.
    Last edited by Bill Greenwood; 01-07-2012 at 01:17 PM.

  2. #22

    Join Date
    Jan 2012
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    Quote Originally Posted by Bill Greenwood View Post
    Mike, as for the compression test, I have mine done when still warm, and I might see a variation of 10 lbs or so; but I would sure be surprised to find a 38lb test that did not indicate an actual problem,and was ok one flight later.
    I think Mike's point about SB03-3 was that compression testing does not replicate engine running conditions and perhaps a slightly sticky valve guide during a "warm" compression test still might cause leakage that would not be present during engine running conditions (high temps and chamber pressures). This is all assuming that one follows the SB's guidance and takes a look-see with a borescope to rule out obvious damage before the one hour flight and re-check.

    Quote Originally Posted by Bill Greenwood View Post
    When we got it home, one cylinder had NO, THAT IS ZERO, compression. Flying it another hour was not going to help; there was actually a pie shape piece missing out of the exhaust valve, just gone, so that I had about 315* of the original
    360* face. I had never seen something that bad. A couple of other ones were low but had some compression.
    The one hour flight would not be done in this case once the borescope inspection revealed the valve damage. The one hour flight is only done when the borescope inspection reveals no damage...

  3. #23

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    Jul 2011
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    Drew, thanks. But you didn't include the part I wrote about being able to hear the air from the compression test leaking out the exhaust pipe. We could clearly hear that,even could feel it with my hand., and it was down on takeoff and climb power. So not counting any other check it was obvious that at least one exhaust valve was leaking a lot. I don't think intake valves leak as often since they run cooler, but if they did the air would go back into the intake. If the rings leaked, the air would go into the crankcase.
    My point was how bad a Continental engine exhaust valve problem can be, such as to have an entire chunk missing on the valve head. I have never seen or heard of that on a Lycoming, certainly not the 3 I have owned. I have seen an Allison damaged by detonation when the line boy put jet fuel instead of avgas in, and it was spark plug damage, nothing like these valves.
    And as for a "sticking valve", yes that can happen, but it is usually on a cold start up, "morning sickness" and frees up as the engine warms up. When I had the big problem first time was spring, after Sun N Fun, so not even cold weather.

    I have looked up Mike's article about this, had even seen it before. I think the use of the borescope to see the color of the valve head is good. it seems to me that there are at least two kinds or qualities of borescope, I am not sure if most shops have the expensive one. I am going to talk to my a&p who is a Beech specialist in Boulder.

    I am not at all convinced however that an engine with compression at 40 is going to produce full power. It is just not logical, that you can be leaking half the air out and have full power. Maybe if none of the leak is past the valves, and it is all going out the rings, the turbo can cover up a lot of that. I know that some older Lycoming engines can still run well for years even is showing some wear.
    I am suspicious that what TCM has really done is just lower the standard on what is considered good. Maybe that is ok. And it is unlikely that is compression is at 40 that all leakage is just the rings. TCM engines don't burn much oil,don't seem to have that much problem with rings; or maybe it is just the the case cracks and exhaust valve failures occur first.
    Other than that, I do like the plane, it is good for traveling. My Mooney 201 was a good plane also.

    I am not an a&p, though am a graduate of Air Force mech school,and have been an owner and pilot for 32 years with experience with 5 different brand of engines, so I have some idea of engine issues.
    Last edited by Bill Greenwood; 01-08-2012 at 11:39 AM.

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