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Cylinder Compression 64/80

T

Trooper11040

Well Known Member
So after a 3.5 month long exhausting avionics install, it was also due for its annual condition inspection. Unfortunately cylinder #3 compression on the o320 fixed pitch was 64/80. Initially it was even lower until I ran the engine after sitting for 3 months. Unfortunately I’m not the builder or an A&P. I don’t believe he will sign my annual off unless I’m over 70. The air is definitely coming from the oil filler tube so it’s getting past the rings. Anyone have a good shop that does an exchange program or anything else I should look into or consider before pulling the jug? This is disheartening as I just spent a ton of $$ on the avionics and now this
 
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Trooper11040 said:
So after a 3.5 month long exhausting avionics install, it was also due for its annual condition inspection. Unfortunately cylinder #3 compression on the o320 fixed pitch was 64/80. Initially it was even lower until I ran the engine after sitting for 3 months. Unfortunately I’m not the builder or an A&P. I don’t believe he will sign my annual off unless I’m over 70. The air is definitely coming from the oil filler tube so it’s getting passed the rings. Anyone have a good shop that does an exchange program or anything else I should look into or consider before pulling the jug? This is disheartening as I just spent a ton of $$ on the avionics and now this
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Some guys have 60 to 65 on every cylinder. No problem. Be happy. Get another mechanic if there is any grief about that cylinder.
 
Let us know how this plays out. The Lycoming service instruction says above 60 should be a recheck at 100 hours. If he's unwilling to sing off on it at 64, I would ask why he's unwilling to follow factory recommendations. I think I would pursue a signature as is with an agreement that you recheck the compression after a few flights and see if it gets better or worse.
 
Fly it like you stole it.
If your guy won't sign it off, I'm only 80 mi S of LRP based at KESN.
I'll work with you.

Mark
 
Trooper11040 said:
This is disheartening as I just spent a ton of $$ on the avionics and now this
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I was given some good advice years ago that the first thing to look at for your condition inspection or before you start any project is to do a pretty thorough look over of the engine including a compression check. This is because if you find anything on the engine it demands primary attention due to lead times, cost, and overall aircraft airworthiness.

I agree with others that 64 does not mean to immediately pull the cylinder.
 
agent4573 said:
Let us know how this plays out. The Lycoming service instruction says above 60 should be a recheck at 100 hours. If he's unwilling to sing off on it at 64, I would ask why he's unwilling to follow factory recommendations. I think I would pursue a signature as is with an agreement that you recheck the compression after a few flights and see if it gets better or worse.
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+1

Find a new mechanic. The general guideline that most in the industry use is anything above 60 is ok and anything below requires investigation and remediation. By moving the bar from 60 -> 70, you magically make more $ from the customer. It is one thing to say the cylinder is getting weak and replacement should be considered. Totally different to hijack your inspection. In this case, the plane sat for a while, so a couple of hard runs may bring it back up.
 
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Trooper11040 said:
So after a 3.5 month long exhausting avionics install, it was also due for its annual condition inspection. Unfortunately cylinder #3 compression on the o320 fixed pitch was 64/80. Initially it was even lower until I ran the engine after sitting for 3 months. Unfortunately I’m not the builder or an A&P. I don’t believe he will sign my annual off unless I’m over 70. The air is definitely coming from the oil filler tube so it’s getting past the rings. Anyone have a good shop that does an exchange program or anything else I should look into or consider before pulling the jug? This is disheartening as I just spent a ton of $$ on the avionics and now this
Click to expand...

A few thoughts,
One, you think your mechanic won't sign it off, but you might be surprised. I routinely tell owners that we should hope to see 70 or better as an indication of good cylinder health, but that doesn't mean I don't sign off readings in the 60s. It just means that a cylinder that can only reach 64/80 needs to be monitored, if only to track progress next year.
And, a short ground run normally will not result in a big change to poor ring seal. You need to fly it for a good 20 minutes AFTER the oil temp has reached normal range.
Also, the ring flush concept is worth trying. It might help, it might not, but it won't hurt to try it.
 
You should find another mechanic. I have been an A&P/I.A for over 45 years and have never suggested that a cylinder be pulled for being 64/80. Find someone that is sensible and knows what he is doing. I will bet if you fly it the compression will come back up. Never pull a cylinder due to a compression check alone, it is a poor representation of cylinder health in most cases.

Best regards,

Bill Wuorinen
Osprey 2 amphibian N137W flying since 2001
RV-7A N237W flying since 2014
 
How does that mechanic work on Continentals? a 64/80 would be pretty good!. Fly it hard, run it lean, run some MMO through it and clean it up.
 
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