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

As Michael was asking do a borescope. This way you can tell if anything is scored and if the walls are glazed over from the oil burn. Unless you find metal, because youve been running it a while with the problem, my guess is its a stuck oil ring. It usually happens with lots of low power flying. The only trouble is the longer you fly it like this way (using oil) the less chance of correcting it without pulling the cylinder.

I have a very similar problem. Sudden increase in oil consumption from 15 hrs/qt to 3hrs/qt. My #5 plugs are sooty up top and oily on the bottom. The right exhaust also became sooty. The compression is good I think 75/80. Did the ring flush which added a few hrs to a qt but still burning 5hrs/qt. Now this wouldnt be bad if it was resulting from 6 jugs but its all going through 1. Flew a couple of hrs at high power which did nothing to free up the ring. So Im toying with the idea of pulling it and doing an IRAN.

I hope all it will need is a new set of rings honing and lap the valve seats by hand since the jug is off.

Michael Ill be speaking to you about this plan shortly.

KHTO, LHTL

C210_Flyer wrote:

my guess is its a stuck oil ring. It usually happens with lots of low power flying.

As in flying long trips > FL100 in a normally aspirated SEP – sounds like the OP’s usual mission !

FAA A&P/IA
LFPN

Exactly Michael.

Thats why I think doing a preventive Cyl. flush is not a bad idea every annual or two. On second thought that might only be 25 hrs of flying in these parts. So make that every 200hrs.

I bought this stuff called liquid Molly at the Aero this year. Its suppose to clean out the cyl via the gas. The only thing is it cleans the Intake valves and seats but not the exhaust. I have not tried it yet. Hopefully they checked to make sure it doesnt eat the fuel lines and diaphram in the spider. The Cyl flush cleaned the exhaust seat for my #1 because it went from 52/80 to 69/80 and cleared the blowby into the exhaust during the compression check.

So while I think LOP and Low HP flying is great for gas consumption, extra procedures need to be implemented to keep the engine happy.

KHTO, LHTL

I did a flight just now, 75-80% power, some 130F ROP (best power) and some peak EGT at 75%. 3700ft or so.

Firstly, no soot in the exhaust. It is clean to touch and a grey deposit:

Top 6 plugs:






Bottom 6 plugs:






This is with the engine running at 1800rpm, very lean, 30 seconds before shutdown. Not what people usually do!

Note that 3 and 5 are the hottest on EGT and CHT and always have been. This shows on the plugs.

So, still the previous pattern with #6 especially being blacker than the other bottom ones, but a lot better than last time. Clearly giving the motor a good thrashing improves things.

And clearly the oil is not going out of the exhaust! What could cause oil to go out of the breather, and how can this be fixed? Normally I keep the level between 7 and 8.

I can’t right away check the oil burn from this flight because it needs a day or so to run back down, and the oil level prior to the flight was about 9.7 qts (7mm above the “9” point on the dipstick) which means some of it will get chucked out anyway. And sure enough there was fresh oil on the belly… So only the next flight will be really useful for the oil burn measurement.

There was no borescope available. My £300 “German” (chinese) endoscope was useless. But one can see most of the cylinder bore via the two plug holes, with a good torch, and all was fine. No brown/honey coloured glazing was evident, and no scoring along the line of the piston motion.

Administrator
Shoreham EGKA, United Kingdom

What could cause oil to go out of the breather, and how can this be fixed?

If oil exiting the breather increases without any changes to hardware, its often gas pressure blow-by past the rings, pressurizing the crankcase. To check this, its often instructive to listen to the breather while doing a compression test (and the exhaust pipes too) as opposed to analyzing the compression numbers themselves. How it can be fixed depends on what you find but in my world if you start having to do black magic on a high time cylinder to reduce blow-by, maybe its time to overhaul it. Obviously high manifold & cylinder pressure (a good thrashing) will help seal rings.

Not a lot of issues in your photos, everything looks normal to me. Lead deposits on plugs suck, wish I could buy 80/87 or 91UL for my planes.

Last Edited by Silvaire at 25 Sep 16:58

Well not being a certified A&P, however I did stay at a holiday in once. I can clearly see a lot of crud in most plugs. Get a dental pick and clean out the lead deposits. Has nothing to do with your problem. But its like watching you kid go off to school without brushing their teeth.

Do you lean on the ground (excessively) and are you LOP on descent to at least short final and then go over-lean on taxi? If you do, then its probably on climbout that your getting all the lead balls in the plugs.

You probably dont have an oil ring problem because the exhaust is as it should be, light brown to grey and not black and/or oily. The plugs look nice and not oily as one would expect. So if you are getting oil on the belly it could be blowby and increased crankcase pressure.. As one possibility. Michael might know of another. However he did not stay at a Holiday INN.

In case it was never aired in Europe.



Last Edited by C210_Flyer at 25 Sep 16:54
KHTO, LHTL

I’ve got some interesting input on this.

Pressurizing the crankcase would cause a loss of oil via the breather. I find this surprising since I thought the breather pipe enters the crankcase above the oil level

Or is the oil loss caused by the air escaping having a lot of oil mixed in with it, so that mere air movement via the breather causes the loss of oil? Apparently this is the reason. Any significant in/out movement of air via the breather will cause oil loss.

There are apparently a couple of ways this can happen. One is bad rings and another is not having a clear breather line.

Not much I can do easily about the rings but the breather pipe can be checked for a blockage.

Also, depending on where the breather exits the airplane, one could suck oil out the breather. According to one specialist, this is common in Lancairs. But this is not something which would suddenly change on a given aircraft.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Or is the oil loss caused by the air escaping having a lot of oil mixed in with it, so that mere air movement via the breather causes the loss of oil? Apparently this is the reason. Any significant in/out movement of air via the breather will cause oil loss.

Yes indeed, and especially true for radial engines – “if a Wright does not spit oil, something must be wrong with it”.
On the other hand, oil loss rate does depend on oil level. My O-360 filled to the max level (8 quarts) loses as least twice as much oil as at 6 quarts.

LKBU (near Prague), Czech Republic

Peter, it’s probably not applicable to your oil usage on the recent flight, but look up ‘crankcase breather whistle slot’. You might find it’s interesting – basically it’s the way many aircraft prevent the engine breather pipe from getting blocked with ice.

Also, my dad’s 1980s homebuilt had an issue early on in which the end of the crankcase breather pipe was in a low pressure area and sucked the sump almost dry in 2 hrs.

Yes I know about that slot. It’s there to enable the engine to breathe should the end of the breather pipe get iced up. Of course they could have made the breather pipe end inside the cowling, but then you get all the sh*t coming out inside the cowling

Your low pressure comment apparently applies to certain homebuilts, where they didn’t check this out properly.

I might investigate getting an oil separator – any experience of these? Some people are very disapproving of them, saying that dumping dirty oil overboard is a good thing…

Administrator
Shoreham EGKA, United Kingdom
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