Engine compressions--trends?

[Richard]

What would the following indicate on a IO-520A?


Engine Compressions:
74 72 70 66 75 72 - Annual 05-10-04
72 74 76 75 77 74 - Annual 04-08-03
75 70 70 65 75 70 - Annual 03-25-02
75 70 65 66 75 65 - Annual 12-15-00
70 70 70 65 75 70 - Annual 10-13-99

 

[Alan]

Keep doing what you're doing?

 

[Dave Krall CFII]

What would the following indicate on a IO-520A?


Engine Compressions:
74 72 70 66 75 72 - Annual 05-10-04
72 74 76 75 77 74 - Annual 04-08-03
75 70 70 65 75 70 - Annual 03-25-02
75 70 65 66 75 65 - Annual 12-15-00
70 70 70 65 75 70 - Annual 10-13-99

Re-check your compression guage/technique ?

 

[Richard]

No, I have no particular answer in mind, this is not a trick question. It's rare that I get to see the history of compression checks on an engine so I thought I'd posted it here to see if I'm missing anything. I like trend spotting but these compressions seem to indicate a healthy engine.

Put another way, in the numbers shown for a specific cylinder, what number(s) would complete the series for each of the next 5 years?

I'm not familiar with the -520 so I wonder why #4 has a history of being lower than the rest. Each engine has it's own picadillos.

 

[waldo]

Not EXACTLY on subject but I got one for you. How about when you look at a log book and see all cylinders 80/80, for the past three annuals? I've seen it logged this way on a plane my brother was looking at purchasing. For those that don't know . . . . what's wrong with this picture?

 

[poadeleted3]

Not EXACTLY on subject but I got one for you. How about when you look at a log book and see all cylinders 80/80, for the past three annuals? I've seen it logged this way on a plane my brother was looking at purchasing. For those that don't know . . . . what's wrong with this picture?

Pencil whipped.

 

[sere]

Your last five years looks normal to me as mine looks a lot like that. I think it all depends on the person testing and how close they are looking at it and also if the engine is cold or hot.

 

[Stache]

Just looking at your numbers I see nothing wrong with them. Compresson checks are designed to identify cylinder leaks that are occuring by the piston rings or in the valve seats area. Compression checks depend on the mechanic performing the test and the compression tester used and did the mechanic use a calibrated orifice. Other factors are when did the mechanic perform the test on a warm engine or cold.

Having more that 5 pounds between cylinders indicates something. I would suggest you perform a borescope of the cylinder and check the valves for seating.

A&P/IA
Stache

 

[zephyr]

It must not have Continental cylinders on it!

 

[Michael]

theres 2 to many cylinders..

 

[Richard]

theres 2 to many cylinders..

The truth comes out. Silly me, all along I've been thinking you got a big bore to go along with that slippery sexy bird. Forget high wing Vs low wing. 4 Vs 6 is what separates the, uhm, from the....nevermind.

 

[Alan]

The truth comes out. Silly me, all along I've been thinking you got a big bore to go along with that slippery sexy bird. Forget high wing Vs low wing. 4 Vs 6 is what separates the, uhm, from the....nevermind.

Huh? All the 520's I've owned were six cylinder. Am I missing something?

 

[waldo]

Pencil whipped.

Absolutely . . . . Compression of 80/80 is impossible. The ring gaps themselves will cause SOME leakage. 79/80 is about the best you can ever hope for on a new cylinder after break-in, and the most that I have seen have been in the 75-78 range with low time on the engines. I am no mechanic but I did sleep at a Holiday-Inn Express once I have owned two airplanes and have helped rebuild both of my own engines. I also have a dozen or so friends that own thier own airplanes so my experience is minimal. Sure helps with knowledge and pocket book when one of your old school buddies is a licensed mechanic

 

[Tom-D]

Absolutely . . . . Compression of 80/80 is impossible. The ring gaps themselves will cause SOME leakage. 79/80 is about the best you can ever hope for on a new cylinder after break-in, and the most that I have seen have been in the 75-78 range with low time on the engines. I am no mechanic but I did sleep at a Holiday-Inn Express once I have owned two airplanes and have helped rebuild both of my own engines. I also have a dozen or so friends that own thier own airplanes so my experience is minimal. Sure helps with knowledge and pocket book when one of your old school buddies is a licensed mechanic

Your theory is good, but in real life we see 80/80 quite often.

 

[gismo]

Your theory is good, but in real life we see 80/80 quite often.

Prolly due to (acceptable) inaccuracies in the gauges although cold oil can stand up against 80 PSI pretty well in a small enough gap.

 

[Tom-D]

Prolly due to (acceptable) inaccuracies in the gauges although cold oil can stand up against 80 PSI pretty well in a small enough gap.

Rings seal pretty well in the bore, because the engine is hot, the piston is expanded as much as it can, and the piston is at TDC where the choke of the bore is the greatest.

Several of my customers have ECI Titan Cerminil cylinders with less than 100 hours on them. You can set TDC, blow 80 psi in the cylinder, and shut off the air supply and the gauge will bleed off very slowly.

You can't hear a leak any where.

 

[gismo]

Rings seal pretty well in the bore, because the engine is hot, the piston is expanded as much as it can, and the piston is at TDC where the choke of the bore is the greatest.

Several of my customers have ECI Titan Cerminil cylinders with less than 100 hours on them. You can set TDC, blow 80 psi in the cylinder, and shut off the air supply and the gauge will bleed off very slowly.

You can't hear a leak any where.

Makes sense. I have wondered why DCT is done at TDC. I suspect it's because it would be difficult to prevent crank rotation elsewhere except BDC where the valves are open. OTOH it seems that if you want to know about ring leakage, it would be better to measure it across the whole stroke.