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How can one detect a broken piston ring (high oil consumption)?

Would a broken piston ring cause such a rapid loss of all oil?

More to the point, would a broken piston ring alone cause high oil temps?

Administrator
Shoreham EGKA, United Kingdom

I don’t see a connection between a broken piston ring and high oil temperature. It’s only the oil sweep ring we’re talking about (that one is not involved in the compression thus the good measurements). I think the mechanic was not unreasonable in his assessment.

If the oil sweep ring is not working, you will have a very high oil consumption, every cycle some oil gets to the hotter area and burns. It can quickly become catastrophic like in MedFlyer’s example. However, I wouldn’t think it’s the combustion gases that created the black burn marks on the piston, it’s the burnt oil. The two compression rings look fine, confirmed by the compression test.

Back to the photos of my plugs, why would the upper ones be all fairly clean while #2 and #6 bottom ones are oily – IF there was a lot of oil getting past the rings?

Is gravity so relevant in the dynamics of the combustion chamber?

Not sure about the mechanic being correct… one should never fly with anything “important” being abnormal, and oil temp or pressure is definitely “important”.

Administrator
Shoreham EGKA, United Kingdom

Peter, whatever the reason is, you have two oily plugs and that can only be the result of mechanical failure.
You’re going to need to pull the cylinders.

Forever learning
EGTB

Not sure it is that clear cut, because all the way back to 2002 I have seen the occassional oily plug.

You can get oil coming through if you get alignment between the gaps of multiple rings. After a while the ring(s) moves around and it sorts itself out. This is not uncommon, AFAIK.

Administrator
Shoreham EGKA, United Kingdom

What’s the EDM telling you?

PS. I’ve seen TIO 540s throw an awful lot out of the breather (i.e. almost a quart an hour).

Last Edited by Dave_Phillips at 21 Sep 05:14
Fly safely
Various UK. Operate throughout Europe and Middle East, United Kingdom

Nothing unusual on the EDM. I watch the temps during flight carefully, though I haven’t yet downloaded the data for the trip to Slovenia/Croatia/Greece.

Administrator
Shoreham EGKA, United Kingdom

Curiously, 2 4 6 are the coolest cylinders

Administrator
Shoreham EGKA, United Kingdom

Peter,
The doubling of oil consumption over a short period is very concerning. Also I would agree that cyls 2 & 6 do not look correct. BTW a rich shutdown should produce a black sooty plug, not a wet oily plug. A boroscope look at the cylinders would definitely be a good idea, picking up slight scoring early could avoid a new cylinder later. If scoring does show I would want to look at the magnetic sump plug and oil filter.

One very cheap test is to listen to the crankcase (through the oil filler neck) with each of the cylinders under pressure, to hear which produces the loudest hiss. If one cylinder is much louder it could indicate a ring problem, even if comps are still within acceptable limits. Also I would look into the exhaust outlet, it should be pinkish grey, not black or dark brown.

I apologise if I’m trying to teach granny how to suck eggs!

I am going to keep a close eye on the oil consumption, and maybe get the two cylinders looked at if it stays as bad as the one flight indicated.

We did use an endoscope yesterday but it was of inadequate quality to show much, though none of the six cylinders showed anything other than the normal criss-cross pattern when looking into the cylinder bores via the plug holes. OTOH one cannot see the whole cylinder circumference that way. And all six looked the same – smeared with a layer of clear oil.

What concerns me about the “must have a broken ring” analysis is that

  • the compressions have always been around 78/80
  • the engine has always run really well and still does
  • CHT and EGTs have never changed
  • oil analysis is good, except there has been a rise in aluminium lately, to 30ppm (on a 50hr old sample) but that’s happened before, and this engine has always been well above the sampling company’s average on the aluminium
  • no metal in oil filter
  • no metal in strainer
  • I have always had some oily bottom plugs, though I never kept track of which ones were oily
  • #2 and #6 (the most oily) have the lowest CHTs!

So there is a lot of contrary evidence. The only thing which seems to have changed is the higher oil consumption, but that was over just one flight. It will need careful and accurate monitoring.

Administrator
Shoreham EGKA, United Kingdom
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