Thorp Air Command - T18.net

I know we have discussed this before, but I couldn't find the thread. Here's some terrible new from today. I have been flying my O320e2d for about 1,000 hours. My compressions have never been stellar. They were about 70 on most. Three years ago, one dropped to 50 and I decided to change the jug. So for the last 3 years, I have had one at 78, two about 68, and one around 60. We discussed putting MMO in the fuel and oil a while ago. I decided to give it a try. I put 8oz in my oil for the last 5 hours before changing it. I've done this for maybe 5 oil changes. Today, Terry and I went up and warmed the oil before starting my annual. She flew ops normal. When I got down and ran the compressions, they were 22, 32, 40, and 28!!!!! We checked three times. As the engine cooled down, the compressions came up. We borescoped the engine and found it to be VERY clean. Question, did I screw up the break in on the cylinders with MMO? That's the only thing I have changed.
I'm looking at a top end overhaul.
Cubes out

Cubes : Regarding the "break in" Aero Sport Power recommended straight mineral oil for my zero time engine for the break in . It was also suggested to limit the ground idle time and to use as much full power airborne as possible during the first 25 hours ? This would help to seat the rings . I would have to look that part up regarding the 25 hours. I have used the MMO in other engines to free up sticking lifters (worked very well) and as a flush prior to an oil change , but I have not used it in an AC engine . Someone out there in engine land might have an explaination as to the sudden drop on all four cylinders ? That is a puzzle as to why all four shit the bed ? Maybe the MMO in aviation oil is breaking it down...not sure ? Have you tried another compression tester ? I would get another tester BEFORE tearing the engine apart . Not sure how the engine would run with all four that low ? Poorly at best !

RB

Cubes, were you able to run the speeds that you normally run? Does the engine feel weak or sluggish, with compression that low it would appear that half of you horsepower would be gone and lifting off would take some effort. With the compression readings you got, there should have been some tell tail signs of a problem this catastrophic, has it been burning a load of oil?...Dan

I was under the impression that as the engine cooled the compression would get worse, aluminum pistons in a steel cylinder. The aluminum expands more than steel, that's why you do your compression checks with the engine warm. Some thing just dosn't seem kosher with your latest results. With compression that low I would expect to get a lot of blow by and elevated oil use, is it burning more oil now than it has been?

When I purchased my airplane the engine had 10 hr on a top overhaul, the compressions were in the mid 60s. 6 years and 200 hrs later I have the best compression yet. I'm running Phillips XC 20W50 oil with 8 oz of Camguard.

_________________
Bruce Finney
N18JF T-18C #262
Yelm, WA USA

With compressions that low you should be out pushing ! Fouled plugs , oil blow by ? I would get another compression tester and do another test or at least do a test on another AC's cylinder to validate the tester you have. Something here does not pass my smell test !

RB

Agreed Rich, something just ain't right here, something just don't smell right. HP is gained with high compression, the result of almost no compression will cut the HP to levels that will be felt if you can even take off. I have run a quart of MMO through my engine just before oil change and I'm all but positive Ira and dean have done the same.MMO has solvents in it and it will clean things up....Dan

Yep..with compression that low it would be VERY hard to start...IMHO. I have used motor flush (Gunk) on all my car engines (changed oil every 3500 miles) and my last engine had 420,000 miles on it . I am not keen on adding stuff to an aircraft engine oil during normal operations . Run the engine (fly) or at least start it up on a regular basis to lube the innards and burn out the moisture . Cubes having all four cylinders acting poorly at the same time and at almost the same compression reading is strange . We need to dig deeper into this ! I use Phillips 20-50 .

RB

I agree. It's sounds funny. I plan to use two different testers tomorrow. I will test cold, then hot. Two mechanics agreed that the comps should come UP in a cooler engine and not down. I thought as you did Bruce. They both said the reason we test hot is that is normal condition of the engine. As far as how it felt, it felt normal. I has Terry in the plane, so a little more GW than I am used to. As far as how much HP I would lose due to low comps, it's anyone's guess. The low comps are all ring blow by. I can hear it in the filler neck. So with bad rings, you may not notice. Remember the piston is really moving fast. It will still keep compression. With the static test we do on the ground, it is a different story. Ill tell you more tomorrow.
Cubes

My 0-320-e2d did that same thing. It ended up being stuck/overheated rings from running the engine too lean the first 10 hours on my plane. I have a per plans airbox, and I had to drill the carb nozzle. Always make sure to check dry tappet clearance when installing a cylinder also.

Thanks Jeff. I was wondering if a re-break in procedure with appropriate oil would work. After I run compressions today, ill call my local engine repair facility.
Cubes

A top overhaul does not have to be expensive. You could hardly ask for a better plane than a T-18 to do it on.
Get your Lycoming direct drive service manual, and start collecting tools.
You can pull your cylinders, dissassemble the parts yourself, hone and re-ring if that is the only problem. Or you can send them out for overhaul, and put them back on when they return.

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Scott Emery
EAA Chapter 326
T-18 N18TE

Yeah I did that to the one that failed a few years ago. So here is what I learned today. Compression testers go bad!,! We used two different testers and got two different results. I finally used the spark plug fitting off the second tester with the valves and gauges off the first. The results were much better. Then I changed to O rings on both and did it again. My final results are fly able. I am now at 67,72, 74, 71!! That is a fair sight better than yesterday morning. Whew! Thanks for all the help guys.
Cubes

Good on ya!
With spring right around the corner, now is no time to be taking the T-18 out of service!

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE

Cubes: A bad tester would have been my first guess . With all four giving bad readings my BS meter would have been pegged . You probably soiled your drawers when you got the good readings ! How long did it take you to reach for a cold one to celebrate ?

RB

Glad to hear that cubes.......Dan