Lycoming TIO-540-AK1A -- Compressions

MikeTuggle

MikeTuggle

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MikeT
There's just not enough info that I can find to tell me whether I am a 'worry wart' or whether cylinder-cylinder differences (above 70/80) are a non-issue.

I was reviewing logs for a purchase candidate and found the following:

Last year's annual was at at 142.5 hours. Compressions at that time were: #1- 78/80, #2- 78/80, #3- 78/80, #4- 78/80, #5- 78/80, #6- 78/80.

At this year's annual, at 190.8 hours the readings were: #1- 70/80, #2- 78/80, #3- 72/80, #4- 78/80, #5- 76/80, #6- 78/80.

Are those differences an issue or a not to worry reading?

Thanks!
 
And done with the same technique? :)

Sometimes, the rings in those big engines don't like to seat unless you get it juuuust right.
 
Anticept said:
And done with the same technique? :)

Sometimes, the rings in those big engines don't like to seat unless you get it juuuust right.
Click to expand...

How did you know it was a big engine?
 
MikeTuggle said:
There's just not enough info that I can find to tell me whether I am a 'worry wart' or whether cylinder-cylinder differences (above 70/80) are a non-issue.

I was reviewing logs for a purchase candidate and found the following:

Last year's annual was at at 142.5 hours. Compressions at that time were: #1- 78/80, #2- 78/80, #3- 78/80, #4- 78/80, #5- 78/80, #6- 78/80.

At this year's annual, at 190.8 hours the readings were: #1- 70/80, #2- 78/80, #3- 72/80, #4- 78/80, #5- 76/80, #6- 78/80.

Are those differences an issue or a not to worry reading?

Thanks!
Click to expand...

Almost 50 hours in a year, with those drops would worry me.
I would be looking for a cause. trying to find where the air is escaping. and why.
 
MikeTuggle said:
There's just not enough info that I can find to tell me whether I am a 'worry wart' or whether cylinder-cylinder differences (above 70/80) are a non-issue.

I was reviewing logs for a purchase candidate and found the following:

Last year's annual was at at 142.5 hours. Compressions at that time were: #1- 78/80, #2- 78/80, #3- 78/80, #4- 78/80, #5- 78/80, #6- 78/80.

At this year's annual, at 190.8 hours the readings were: #1- 70/80, #2- 78/80, #3- 72/80, #4- 78/80, #5- 76/80, #6- 78/80.

Are those differences an issue or a not to worry reading?

Thanks!
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The numbers are kinda irrelevant. What you want to do is listen for where the loss is. Stick your ear to the exhaust pipe. Do you hear the flow of air? If so, you have a problem regardless the number. The higher the number the more likely you can fix the problem for a few hours labor and a few dabs of lapping compound and some Berryman B-12 spray to clean the stem.

If you hear the air leaking at the case vent pipe, you don't particularly have a problem to worry about, especially if you can pull 65/80+. A lot depends on oil consumption. You may want to peek in the cylinder with a bore scope or whatever and look for cylinder scoring. If you aren't seeing scoring happening and aren't using too mu oil, there's no immediate worry.
 
Henning said:
The numbers are kinda irrelevant. What you want to do is listen for where the loss is. Stick your ear to the exhaust pipe. Do you hear the flow of air? If so, you have a problem regardless the number. The higher the number the more likely you can fix the problem for a few hours labor and a few dabs of lapping compound and some Berryman B-12 spray to clean the stem.

If you hear the air leaking at the case vent pipe, you don't particularly have a problem to worry about, especially if you can pull 65/80+. A lot depends on oil consumption. You may want to peek in the cylinder with a bore scope or whatever and look for cylinder scoring. If you aren't seeing scoring happening and aren't using too mu oil, there's no immediate worry.
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My worry would be the big change, WHY>?

Scoring on all cylinders equally. WTF.?
 
Henning said:
Exactly, why is the question. There's only 2 main possibilities, rings and exhaust valves.
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No, No, No, it may be two different gauges one with a leak. or a multitude of other stuff.

Never make assumptions that the first one was right.
 
Tom-D said:
No, No, No, it may be two different gauges one with a leak. or a multitude of other stuff.

Never make assumptions that the first one was right.
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On the rings issue I agree, but listening to the exhaust comes first. If I see a low reading and hear it coming out of the exhaust valve, I have a problem even if I can jiggle the prop and get the valve to seat, and the sooner I address it, the cheaper it will be.
 
Henning said:
On the rings issue I agree, but listening to the exhaust comes first. If I see a low reading and hear it coming out of the exhaust valve, I have a problem even if I can jiggle the prop and get the valve to seat, and the sooner I address it, the cheaper it will be.
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And when there is no leakage and your gauge shows 40PSI, what then?

Do you ever ask your self what else can it be?

I've had my compressor fail, I have had my gauges fail.
It's not always the engine.
 
Tom-D said:
And when there is no leakage and your gauge shows 40PSI, what then?

Do you ever ask your self what else can it be?

I've had my compressor fail, I have had my gauges fail.
It's not always the engine.
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:confused: Then you know you have a non engine related problem. Where is any of this relevant. :confused::dunno:

If you have a bad reading you check the exhaust first. If you don't hear it in the exhaust, you don't have any grave concern with the numbers given in the OP.
 
Henning said:
:confused: Then you know you have a non engine related problem. Where is any of this relevant. :confused::dunno:

If you have a bad reading you check the exhaust first. If you don't hear it in the exhaust, you don't have any grave concern with the numbers given in the OP.
Click to expand...

It's relevant because we don't know that either test was done properly. And I disagree that you check the exhaust first. I first insure I was doing the test correctly.
 
Tom-D said:
How did you know it was a big engine?
Click to expand...

Because of the TIO-540 stated in the title :). I consider that a meaty engine. Not the meatiest, but does have decent diameter bores. Once in a while I will get an engine where the rings get a little ornery and don't like to seat very well during the test. Run it some more and start over!
 
Last edited:
Given the uncertainty vs. a "don't worry" consensus, I will try to speak with the shop that did the annual.

This isn't HIPAA (US health info confidentiality), so I think they'll tell me what they have in their notes from last month.

Thanks!

P.S. The plane is a T182T Skylane.
 
I wouldn't worry about it at all.
 
Tom-D said:
And when there is no leakage and your gauge shows 40PSI, what then?

Do you ever ask your self what else can it be?

I've had my compressor fail, I have had my gauges fail.
It's not always the engine.
Click to expand...


How is that not instantly noticeable..:dunno::dunno::dunno:

After all,, it is the second number in the test .... 75 / 80....:idea::idea:
 
I'd fly the plane at a high cruise power setting for an hour or two and test it again.
 
Ted DuPuis said:
I wouldn't worry about it at all.
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Neither would I, I would suspect one test was done hot, and the other one was not.

I do these big bores cold, it is easier to detect a stuck valve (like morning sickness) cold, because hot they seal up. and work normally.
 
My opinion is that most "Ooh, that could be bad" exercises end up doing little beyond creating a science experiment that costs the owner a lot of money. Keep in mind that maintenance has its dangers, too. On a FRAT I'm familiar with, the maximum risk score (5) is assigned to first flight after MX, and that score was insisted upon by a specialty shop.

If the engine is telling you there's a problem, then yes, that's worth looking into. Seeing some cylinders go down to 70 from 78 in one year? Don't bug me a bit unless you're observing morning sickness, EGTs that could indicate a burned valve with potential issues, etc.
 
Get a cheap dental camera ($50) on ebay....and have a look see inside the spark plug hole. That will tell you way more than a compression value any day.

I've purchased several of these and this is money well spent.
 
Spoke with the A&P this morning.

He isn't concerned at all about the 70/80 or the 72/80 compressions on cylinders 1 and 3.

To answer other posts and questions, "The compression test was done hot. I took it out and ran it for a while. Did the other 'running engine' tests and then came back in and did the compression tests."

We had this entire discussion without reference to what plane I was asking about. At the end of the call and after I gave him the N-number, he looked at his file folder from the inspection and there was nothing remarkable there.
 
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