Question for IO-550G Owners

[jax88]

At what point would you worry about the compression in your cylinders?  Would you be alarmed if 3 of your cylinders could only be coaxed into a compression of 60 while the other three were 68-70?

[N513ZM]

Quote: jax88

At what point would you worry about the compression in your cylinders?  Would you be alarmed if 3 of your cylinders could only be coaxed into a compression of 60 while the other three were 68-70?

[jax88]

Sorry, don't have any other details.  Just reading engine logs of prospective aircraft and found the discrepancy in the compressions a bit alarming.  But instead of making an uneducated decision I thought I'd seek out some advice from those that fly behind the 550G.

[carusoam]

Jax,

I think this is a question that can be opened up to the continental crowd in general.  Compression readings on continentals live in a different range than what Lycoming mandates.

I am unsure of specific details but it is worth looking further.

Mikes comment about oil burn rate is probably most significant.  Many 550-Gs hardly burn oil at all compared to an ordinary Lycoming O-360s.  If you can get oil use data from the owner, that would probably be more telling than the compression data.

The engine logs should indicate if there has been any cylinder work since new or OH.

Best regards,

-a-

[Kwixdraw]

Adding Carosome's comments. Continental engines take a knowing touch to get good compression readings.  You can work the prop a bit to help pressurize and seat the rings and get a pretty fair fluctuation in the numbers. They also depend somewhat on the equipment that the A&P is using too. Continental specifies that they want a differential compression tester with a "master orfice" which evens out the readings and makes them fall more in line with Lycoming numbers. You may find some mechanics that don't have that type tester and will have different figures than someone else who tests it. You may want to consider what the readings are on cylinders that are opposite each other on the crankcase. Lycoming specifies a max differential from opposing cylinders but Continental does not, to my knowledge. Still not a bad thing to consider IMO.

[tyrefoote]

try reading the article on pre purchase inspection of M20R-S

http://mooneypilots.com/mapalog/M20SR_prepurchase_inspections.html

[jax88]

Aircraft had a prop strike at 1300 hours, Penn Yann did the teardown and inspection, crank case had lap and linebore repair by DIVCO, no damage noted and engine reassembled.  #4 cylinder was replaced at 1584 hours, #5 cylinder was replaced at 1790 hours.  Last annual at 1880 hours DOES include a master orifice reading of 43.  Cylinder compressions were 69/52/72/70/76/64.  No metal found in any of the oil/filter inspections going back to prop strike.

[carusoam]

Jax,

At 1880hrs on a 2,000 hour TBO....are you looking at an OH or trying to stretch as far as you can?

Run it and recheck the compression on the 52?

Best regards,

-a-

[jax88]

Hoping it has a couple years of life left, thus the question about compressions.  Trying to determine if the compressions are an indication that it is ALREADY time for an overhaul.

[DonMuncy]

Go to the manufacturer's web site and see what they recommend as a minimum. Even at that, I wouldn't worry if it were a little below that minimum. If the oil consumption is low enough to satisfy you and the engine is not making any metal, it will keep on going without any serious effect. I think I read somewhere that someone ran an engine withour any rings, and the power was within 10 % of the rated number.

Don

[Kwixdraw]

I'd want to see the work order on that sudden stoppage inspection. I don'r know why anyone would take an engine down that far and not put new rod and main bearings in it, especially considering that they did case work. You may just be looking at top end issues.