Compression numbers after overhaul

[Quint Van Deman]

Hello all--

I just came out of my first annual after overhauling the engine (70 hrs on the new engine). In reviewing the logbooks the compressions were 73,73,74, and 76.
I've seen where Lycoming says anything about 70 is normal, but most reports I see like compressions around 78. I haven't talked with my mechanic about these numbers yet, but does anyone here have any thoughts?

Thanks,

-Quint

[Zach Grant L1011jock]

Fly it and dont worry about it! I know you have had many issues in the past, but as long as you arent burning oil, I would guess those are cold numbers and are quite normal. Fly more and recheck hot, and you will probably have 78ish numbers....
-Zach

[Kristin Winter]

Also, different compression testers check differently. There are really two different sized orifices the testers are supposed to use. One is .040 for cylinders with a bore of less than 5" and .060 for cylinders larger than that. The Lycomings are just over 5". If the A&P used a tester with the smaller orifice, the compressions might read a bit lower. Fly and see what happens.

[steen]

Congratulations on your "new' engine.
Don't know if you went with new Lycoming cylinders,chromed,nickled, original overbored, etc. so can't really know whether your numbers
are abnormal, but I suspect not.
Kristin and Zach gave good advice and the real numbers will be found at 500-1000-1500-2000 hours. I suspect that if you fly regularly the numbers
won't change and may even improve.
Enjoy your Lycoming and don't baby it but maintain it and enjoy!!
Steen

[Quint Van Deman]

Thanks all (and forgive my paranioa!).
Nothing alarming on the oil consumption side, so I'll take the advice and just keep her in the air as much as possible!

The new cylinders were new Lycomings if that makes a difference.
In doing a bit of poking around myself, the only thing I note as being out of the ordinary thus far is that it had Phillips 66 X/C 20W50 in it from hour 0, instead of straight mineral oil as I see repeated numerous times here. Hopefully that doesn't come back later on.

On the plus side, I have EDM data from hour zero, which shows everything as right where it should be for EGT/CHT. The indicated fuel flow still seems to swing fairly wildly every couple of minutes or so, but I haven't been able to correlate that with anything else.

Thanks,

-Quint

[JIMICS2452]

Phillips 20/50XC is mineral oil. The overhaul shops I have had contact with in the last 10 years insist on it or Phillips 20/50M (no dispersant additives). I have used it for 15 years with great results.

Jim Hiatt

[Quint Van Deman]

Thanks Jim.

You're right in that I was talking about the addition of the ashless dispersant (the "M" vs. "X/C").

In reading this: http://www.lycoming.textron.com/support ... ations.pdf
It spells out:
The first careful consideration for engine run-in is the oil to be
used. The latest revision of Lycoming Service Instruction 1014
should be consulted for this information. The basic rule which
applies to most normally aspirated Lycoming piston engines is
simple: use straight mineral oil of the proper viscosity for the
first fifty hours or until oil consumption stabilizes. Then switch
to ashless dispersant (AD) oil.

Have you used Phillips 66 X/C 20W50 during a break in period with good success?

[JIMICS2452]

Yes, on the last engine I had overhauled. It is a TIO540C1A on a turbo Aztec. I noticed no difference from earlier engines (O-540A1D5 on my Comanche).
Jim Hiatt

[Quint Van Deman]

Thanks Jim.

Interestingly Phillips own recommendation is for X/C over M: http://www.phillips66aviation.com/lub_matrix.aspx

I suppose I'll put this also into the "don't worry about it" bucket.