Engine compression?

Tom-D said:
And you believe your opinion is better than another. If you can tell where the seat is not sealing, show us the proof.
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ok....here's proof.
 

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Tom-D said:
That's not proof, it's just more pictures.
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do you need a scratch and sniff too?.....Tom the compressions on that was below 30/80. I have the engine monitor CHT data too. But, that may be a bit much for ya. :confused:
 
Silvaire said:
There's no such thing as the "start of a burnt valve". If you have an actual visual indication then it's burnt and the compression test is already telling you that without even looking. All of this came from the Continental service bulletin then Mike Busch took those pictures and started the myth that you can just look in there with a borescope and foretell the future. Problem is that all of those pictures are from cylinders that failed compression tests and were removed. Those visual clues don't foretell the future, those valves are already burnt and they already knew it before taking a picture of it because it was leaking like a sieve.
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So you don't need the compression test? A borescope would do just as well.
 
Checkout_my_Six said:
do you need a scratch and sniff too?.....Tom the compressions on that was below 30/80. I have the engine monitor CHT data too. But, that may be a bit much for ya. :confused:
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The pictures don't show that. you can't see the damage in those pictures. It all must be taken apart and cleaned up before you can see anything.
 
it doesn't have to be green.....again the irregular heat...or lack of cooling will cause the shape to be non-circular.
 
Checkout_my_Six said:
it doesn't have to be green.....again the irregular heat...or lack of cooling will cause the shape to be non-circular.
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Agree with you, but in that particular case, the color helps to pinpoint where the leak occurs.
 
it does....but I have my own pictures. ;)

green is very bad. They will leak way before they turn green.

Here are a few more that were not leaking.....note the circular pattern. Compression was fine.
 

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Cap'n Jack said:
So you don't need the compression test? A borescope would do just as well.
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No, the opposite. A compression test is going to tell you what’s going on long before you’ll see anything with a scope.
 
Chesterspal said:
So, to be clear on this...

If the compression check shows a healty 73 to 76 on all four cylinders, regardless of discoloration seen inside with a camera, leave things as they are for now and keep flying.

Is this correct?
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Tom-D said:
yes
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Checkout_my_Six said:
do you need a scratch and sniff too?.....Tom the compressions on that was below 30/80. I have the engine monitor CHT data too. But, that may be a bit much for ya. :confused:
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The cylinder you photographed doesn't meet Tom's criteria for the "Yes" he posted.

You're being disingenuous again.
 
I attended the AOPA fly in Frederick MD this past weekend, and Adrian Eichhorn was teaching a maintenance class which discussed this exact topic. I also got the above-referenced poster from AOPA defining the anatomy of a valve failure. A couple of lessons which are applicable here they covered:

First, they discussed the process of compression tests and what it actually means in terms of your engine. I was surprised to find out that, while it can be an indicator of need to further explore/inspect, it does not have a lot to do with failure unless the compressions are drastically low.

Second, utilizing a borescope (or some other version of small camera) they taught us how you can find two attributes of a valve that warrant further inspection and/or repair:
  1. If you find a spot that is inconsistent like the crescent shape previously mentioned, it means that likely the valve rotator is malfunctioning (which can be tested without full disassembly/removal of the cylinder first), and
  2. The discoloration toward green indicates uneven heat distribution as an effect of #1.
Next time I am doing maintenance I'm going to check out my O-470's valves. Should be interesting to see what the internals of my near-TBO engine are looking like.
 
sardonux said:
I attended the AOPA fly in Frederick MD this past weekend, and Adrian Eichhorn was teaching a maintenance class which discussed this exact topic. I also got the above-referenced poster from AOPA defining the anatomy of a valve failure. A couple of lessons which are applicable here they covered:

First, they discussed the process of compression tests and what it actually means in terms of your engine. I was surprised to find out that, while it can be an indicator of need to further explore/inspect, it does not have a lot to do with failure unless the compressions are drastically low.

Second, utilizing a borescope (or some other version of small camera) they taught us how you can find two attributes of a valve that warrant further inspection and/or repair:
  1. If you find a spot that is inconsistent like the crescent shape previously mentioned, it means that likely the valve rotator is malfunctioning (which can be tested without full disassembly/removal of the cylinder first), and
  2. The discoloration toward green indicates uneven heat distribution as an effect of #1.
Next time I am doing maintenance I'm going to check out my O-470's valves. Should be interesting to see what the internals of my near-TBO engine are looking like.
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I was there too..... ;)
 
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