Greg Ellis Posted August 12 Report Posted August 12 Would anything show up on an EDM 900 with a cylinder that has two broken piston compression rings? Plane flew fine but had zero compression on a cylinder with a compression test. When cylinder was removed the piston rings fell in pieces onto the hangar floor. Forgive my ignorance if this is a stupid or obvious question.
Jim F Posted August 12 Report Posted August 12 Well that's interesting, Were you able to make static RPM (~2650rpm) on the runway before take off (before you start rolling)? I would think the EGT and CHT would be low and static RPM would be ~100rpm low
KSMooniac Posted August 12 Report Posted August 12 I don't think an engine monitor would show anything. The engine will run and produce power without rings, but will likely blow a lot of oil out and give you a messy sign. 1
EricJ Posted August 12 Report Posted August 12 +1 that it is likely to run just fine with broken rings. Also +1 that oil consumption will likely be up and the amount of crap getting out the vent onto the belly will likely increase.
Greg Ellis Posted August 13 Author Report Posted August 13 3 hours ago, Jim F said: Well that's interesting, Were you able to make static RPM (~2650rpm) on the runway before take off (before you start rolling)? I would think the EGT and CHT would be low and static RPM would be ~100rpm low Yes. RPM. Was normal.
Greg Ellis Posted August 13 Author Report Posted August 13 Oil consumption went up drastically but I am not sure where it went because the belly was clean. I flew for 45 minutes and went through a quart of oil. 1
Jim F Posted August 13 Report Posted August 13 13 hours ago, Greg Ellis said: Yes. RPM. Was normal. Then you were making close to rate power. So i would concur with KSMooniac and ErikJ you would not see a difference in EGT or CHT. The oil went into the combustion chamber and was burnt during the power cycle. Any idea what caused the rings to break?
Greg Ellis Posted August 13 Author Report Posted August 13 52 minutes ago, Jim F said: Then you were making close to rate power. So i would concur with KSMooniac and ErikJ you would not see a difference in EGT or CHT. The oil went into the combustion chamber and was burnt during the power cycle. Any idea what caused the rings to break? Not a clue and nothing was offered up by the A&P. The cylinder was actually running nice as well. Never got hot on the engine monitor. At annual which was in February it had a lower compression in the upper 60's and the A&P mentioned it. Lycoming recommends if in the 60's to continue to fly it and monitor it so that is what I was going to do. So something happened between February and July. 1
Jim F Posted August 13 Report Posted August 13 Is there a flight that you remember the oil consumption significantly increase? If so, download the flights just before and send to Savvy and maybe post here. You dont see a lot of broken rings.
MikeOH Posted August 13 Report Posted August 13 Could insufficient ring end gap clearance at assembly be responsible for this?
kortopates Posted August 13 Report Posted August 13 Could insufficient ring end gap clearance at assembly be responsible for this?Yes, in the cases i’ve seen though it resulted in high CHTs and chewed up the cylinder walls pretty bad. So cylinders were replaced. This is more of a Superior cylinder issue because the installing A&P has to assure proper ring gap at installation whereas other cylinders usually come already properly gapped so it can be missed when the installer doesn’t read the provided documentation and warnings that come with Superior cylinders. Sent from my iPhone using Tapatalk 5
N201MKTurbo Posted August 13 Report Posted August 13 When I did my engine a couple of years ago, I used Continental (ECI) cylinders. I pulled the rings off one piston to set the gaps. They were all dead nuts on. So I left the other three alone. 2
Jim F Posted August 15 Report Posted August 15 On 8/13/2025 at 2:46 PM, kortopates said: Yes, in the cases i’ve seen though it resulted in high CHTs and chewed up the cylinder walls pretty bad. So cylinders were replaced. This is more of a Superior cylinder issue because the installing A&P has to assure proper ring gap at installation whereas other cylinders usually come already properly gapped so it can be missed when the installer doesn’t read the provided documentation and warnings that come with Superior cylinders. Sent from my iPhone using Tapatalk Hi Paul, I agree that too tight of end gap is most likely the cause, but I would think this would happen in the first 10 hours or so. Not sure i saw the time on this cylinder, but that piston looked like it had more the 300hr on it. 1
kortopates Posted August 16 Report Posted August 16 Hi Paul, I agree that too tight of end gap is most likely the cause, but I would think this would happen in the first 10 hours or so. Not sure i saw the time on this cylinder, but that piston looked like it had more the 300hr on it.Absolutely concur. Sent from my iPhone using Tapatalk
201Steve Posted August 18 Report Posted August 18 This is an interesting topic and one I’ve been wondering about myself. I’ve been seeing larger than usual spotting in the hangar out the breather tube. Oil consumption is less than stellar somewhere in the 3-4 hours per quart range, oil analysis shows consistently high chrome, but Boroscopy hasn’t revealed any smoking guns so I haven’t worried about it too much just waiting on any further signs of distress. “Compressions” as the alt test that could isolate one cylinder hasn’t pointed one out. Gosh if we could just have a looksie at rings and cams without major surgery we’d nearly put the forums out of business bc there would be nothing to talk about. Haha. Air cooled piston aircraft engines are just a perfectionists nightmare. 1 1
Andy95W Posted August 18 Report Posted August 18 26 minutes ago, 201Steve said: Air cooled piston aircraft engines are just a perfectionists nightmare. +1
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