Cylinder change did not improve compressions

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4RNB

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4RNB
I am looking at a 182 for sale, reviewing the logs. I think in 2018 or 19 a cylinder was replaced when compressions read 64/80. After the change compressions remained the same. Should I be worried about anything as I evaluate the plane? Any thoughts?
Thank you.
 
There should be six readings... if they were all that low (and if they were all fairly the same number and that low, seems odd to change ONE cylinder), that itself isn’t a show stopper.

If just that one cylinder was low and they changed it, and it didn’t get better, that’s weird.

we really don’t know enough to make a good recommendation right now. But on the surface, something is a little wrong.
 
In 2006 engine was disassembled and sent out for power section overhaul only. Crankcase sent out to Aircraft specialties. Cylinders overhauled by Western Skyways.
In 2017 all numbers in the 70's, #6 was 77/80
2018 was 72-76 except # 6 was 64. Handwritten and perhaps tough to read it said # 6 was changed due to low differential pressure test 58/80. This was at 800 hours on engine.
2019 All were 76 or 78 except # 6 was 64.
In 2020 everything except # 6 was 76 or 78. #6 was 64.
This year all were 74 except # 6 shows up as "53/43 #6 is test port pressure on replacement cylinder"
I do not understand the test port entry?
 
Hmmm... cylinder not broke in yet? Run compression checks on a pre buy?
 
Why would they replace a cylinder for being at 64? Seems pretty normal for a 182. I had one in the 60s, mechanic told me to fly more and it would come up, so I did and it did. You never know if the mechanics are taking them hot or cold (I’ve asked and some have told me cold - it’s supposed to be hot) or what little thing is different from today than yesterday, but I personally wouldn't be too worried about a cylinder at 64.
 
What engine are you referencing? Later model 182s are Lycoming and earlier models are Continental.
 
Clip4 said:
What engine are you referencing? Later model 182s are Lycoming and earlier models are Continental.
Click to expand...

Continental 0-470-U17B
 
4RNB said:
I read some stuff, including from Busch, but do not understand.
What do those numbers mean for that cylinder? Talk to me like a high school kid...
Click to expand...

It means there's leakage somewhere.

The differential compression tester has two gauges on a block that has a calibrated restriction between those gauges. That restriction causes the pressure to fall as more air moves through it. The first gauge measures the incoming pressure, and we set that to 80 PSI with the regulator. The air then passes through the restriction to the second gauge and to the cylinder being tested. If there is no air movement---nor leakage anywhere---the second gauge will read the same as the first. Pascal's Law. Can't have a pressure drop if there's no movement. A leak causes air movement, the restriction causes drag that reduces the pressure at the second gauge, and more movement (bigger leak) means a bigger drop at the gauge.

So we get a number like 60/80, meaning that we have set the incoming air at 80 but the second gauge is saying 60. A moderate leak somewhere. We want to make sure it isn't our tester or the hose or the fitting we put in the sparkplug hole that's leaking, of course. Then we listen at the oil filler hole; if the rings are leaking we'll hear it there. If we hear air at the exhaust, it's an exhaust valve leaking. At the induction air inlet, it's an intake valve. We sometimes have to wiggle the prop a bit to make sure the rings seat properly in their grooves or we'll get a falsely low number.

78/80 is a good number. 60/80 I did not like at all. If the exhaust valve is leaking, it's just going to burn and cost more money if I don't fix it now. Continental is satisfied with numbers like 43/80, but that had better be mostly ring leakage, in my opinion.

That 53/43 number likely represents two different takes on the test on that cylinder. Maybe the rings aren't seating properly. I wouldn't know; I'm not there doing the test. The test should be done with the engine warmed up.

proxy-image
 
Thank you. I talked to a local and suggested maybe they did not really put a new cylinder on, maybe just did something to what was there like change rings.
Local guy told me to be concerned about the cam shaft though he liked the outfit that overhauled it. He suggested factory new.
 
I’d contact the cylinder overhaul shop and ask for the repair record to see what repair work was actually performed.

was:
  • Cylinder re-honed?
  • Valves honed or reground?
  • Vale seats replaced?
  • Valves replaced?
  • Valve guides re-honed or replaced?
  • Roto coil tested/ replaced?
  • From the A&P: what’s the new ring gap if cylinder rehoned? Were the rings regapped?
After installation with differential pressure testing, where’s the air leaking? To crankcase, intake, exhaust system?

With that foundation of fact we can better help.

Also the rings rotate and occasionally the ring gaps line up with each other showing low compression. The last differential pressure test could be just dumb luck the rings lined up. If air leakage is to crankcase, then fly for a while and retest.
 
Last edited:
NordicDave said:
I’d contact the cylinder overhaul shop and ask for the repair record to see what repair work was actually performed.

was:
  • Cylinder re-honed?
  • Valves honed or reground?
  • Vale seats replaced?
  • Valves replaced?
  • Valve guides re-honed or replaced?
  • Roto coil tested/ replaced?
  • From the A&P: what’s the new ring gap if cylinder rehoned? Were the rings regapped?
After installation with differential pressure testing, where’s the air leaking? To crankcase, intake, exhaust system?

With that foundation of fact we have better help.
Click to expand...

I contacted the sales agent who had not read the log books, was not aware of what was going on with cylinder 6.
She was to have someone else call me back in 15 or 20 minutes, would not give me the owners number direct to ask the story on this.
It has now been 40 minutes without a return call...
 
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