Ring Chatter (or slap)

[piperboy84]

Anyone had this or want to take a stab at explaining its causes and symptoms. I'm hopefully reaching the end of the road in getting my engine running properly again after a tear down and inspection. Ring chatter is what the mechanic said was wrong with one of my cylinders. I want to arm myself with some knowledge on the subject.

Edit to add: 4 pot Lycoming

[Big Pistons Forever]

The only time this would be an issue in a normally aspirated engine that is properly set up is at very high altitudes like 15 K +. To generate enough power to hold altitude you have run with high RPM but the max MP will only be in the teens and there will be not sufficient cylinder pressure to hold the rings firmly against the cylinder walls.

The result is scuffed cylinder walls and damaged rings. I have only seen this once in a C 182. After the owner insisted in in trying to cruise at very high altitudes his next annual found all of the cylinders with very low compression and a lot of blow by past the rings. 12 K USD for 6 new cylinders fixed the problem :ugh:

[Above The Clouds]

Are you sure its the rings and not pinking from the ignition timing not being set correctly ?

[Talkdownman]

Wondered what this was about. Obviously clicked on for the wrong reasons...

[piperboy84]

This is a follow up thread from another I started last spring when I had a prop strike, the engine was torn down and inspected as per the FAA regs but never ran right when I got it back ( the aircraft is only 8 years old and the engine had 275 SNEW when the incident occurred) . I've spent the last 9 months taking it back to the engine shop trying to zero in on the problem after many misdiagnoses and unneeded fixes and tweaks that didn't solve the main issue. Specifically the bottom plug on cylinder number 1 kept gunking up at low rpm, running a fine wire (hotter burning) plug would fix the rough running I assume by burning up the oil that was fouling it when testing the mag that was related to that bottom plug, but if I put the regular plug back in it would foul up again when taxiing or operating at low rpm. It was agreed with the insurance and engine shop that a brand new cylinder/piston/ring kit would be installed which they are doing now. Prior to starting the job on Thursday the mechanic told me the problem was caused by "ring chatter"' which he describes as the join part of the ring not being seated correctly allowing oil past and through onto the plug which gets fouled up then causes a misfire unless it is cleared with excessive leaning during run up. The reason I asked the question is this isn't the first time I've been given a new explanation for the problem then after the recommended fix the issue resurfaces, I want to better understanding what he is telling me about this "ring chatter" which worryingly is at odds with what BPF describes and the compression checks come back within tolerance which also leads me to doubt the mechanics opinion.

Edit to add: ATC I had the timing verified by a second shop so I know that's not the issue.

[noflynomore]

Did they rehone the bores during the rebuild?

http://www.championbrands.com/EP07-2009_58-62.pdf

[piperboy84]

Yes they re honed all cylinders, then redone number 1 when it had problems

[effortless]

Piston slap was quite common in older motorbike and older aero engines. It used to be very common in police triumphs sold on to the public. It was the sign of being well used. It tended to reduce as the engine warmed up. Ring slap is when the ring journals are a bit worn so the ring isn't stable in the piston. This was very rare and I can't really see the cause unless the bore is so worn that the ring wobbles. It could be because the wrong oversize ring was fitted after a rebore.

[Weeds round the prop]

I have followed your sorry tale from the start and you have my sympathies.
Is this effect/problem also an audible effect or visible as witness marks on the bore?
I must admit to not having heard this term before, and have spent much of my hobby life inside engines of one sort or another (not my profession) but have no experience of aircraft power units apart from reassembling a C65 and a C90.
The rings should be a good running fit in the grooves so I cannot see how any chatter can occur especially at the RPM that this will operate. I fail to see how any effect can be caused by the ends of the ring assuming that it is 'gapped' correctly, and I think modern automotive and small engine rings are supplied to size these days although I always check square in the lower part of the bore.
Strange!

[Crash one]

Duncan,
This saga has gone on so long that I find it a bit strange. These Lycosaurus engines are pretty much bullet proof, any engineer and his dog in this aviation business should know all that needs to be known about them by now.
I've never heard of the term "ring chatter" but would assume it means worn ring grooves, rings moving up and down in the grooves, piston slap is not the same thing, that's worn sloppy pistons swinging side to side as they move up and down the bore. This engine has been stripped apparently more than once?
I'm beginning to think someone is pulling woolies.
I've had a few faults in my own engine, stuck needle valve, half dead magneto, worn valve guides. And in every case the fault has been identified correctly and fixed correctly with no further trouble.
I don't know what the maintenance regime is on N reg or if the a/c is in UK or US, but I would recommend a word with my LAA engineer, in Tranent.
I don't even know if he is allowed to advise/look. If you want a third opinion PM for his details.

[Crash one]

Also there are only two ways that oil can get into the cylinder. Past the rings or down through the valve guides.
If you are getting good compression then it can only be the valve guides.
Fitting a new cylinder/piston/ring set should solve the problem but is a bit of an overkill.
A new set of valve guides, and perhaps new valves would, in my opinion, fix it.
Just my two pennorth.

[piperboy84]

Also there are only two ways that oil can get into the cylinder. Past the rings or down through the valve guides.
If you are getting good compression then it can only be the valve guides.
Fitting a new cylinder/piston/ring set should solve the problem but is a bit of an overkill.
A new set of valve guides, and perhaps new valves would, in my opinion, fix it.
Just my two pennorth.

Crash, I too think replacing the cylinder/piston/ring kit is overkill, and I also suspect "ring chatter" is another misdiagnosis and have thought the valves were the source of the oil pass thru. However I'm at the end of my tether with this and as it's the insurance that's picking up 100% of the cost and I'm sick to death of being told it's problem X then when that is proven wrong its problem Y then that is also wrong etc, etc, I have put the insurance and engine shop ( a highly reputable outfit) on notice that this is the final attempt at a fix that I am going to allow and if it does not rectify the problem I want a brand new engine, not an overhauled or factory remanufactured one but completely new firewall forward setup and I don't give a flying f$&k if they come back again with another theory of what's causing the problem it's either a brand new set up or it's the lawyers. This aircraft should have been back in Scotland last summer but this issue has delayed its shipping. I truly wish I'd never bothered reporting the incident or making a claim and just bought a replacement prop and stuck it on myself right there next to the taxiway the day after the incident, them unbuttoning the engine for inspection has caused endless problems.

[Big Pistons Forever]

I truly wish I'd never bothered reporting the incident or making a claim and just bought a replacement prop and stuck it on myself right there next to the taxiway the day after the incident, them unbuttoning the engine for inspection has caused endless problems.

I feel your pain however the prop strike inspection is really important. A fellow I know used to run a maintenance shop . One day a guy brought in his C 185 to get the prop balanced because he thought the engine was not quiet as smooth as his last airplane.

The shop had an electronic vibration analyzer which would specify where to put the spinner balance weights. The problem was the machine kept on giving difference answers. When an engine shop was consulted the first question they asked was "did the engine have a prop strike". The owner said no, but further investigation revealed that the serial number of the prop had mysteriously changed. Turned out the previous owner had left the airplane unsecured and a wind gust had tipped it on its nose bending one prop blade. He just slapped a new prop on and said nothing. :hmm:

The engine was removed for inspection and the engine shop reported that the front bearing web was cracked almost all the way through and the engine was hours away from a catastrophic failure.......

[ShyTorque]

I'm not an aircraft engineer but have built quite a few other engines in my time, as an amateur. Isn't ring chatter caused by incorrect cylinder honing angle? The rings effectively "bounce" over the grooves left by the honing and don't bed in properly and don't scrape the oil as they should. This allows oil to reach the combustion chamber.

If your mechanic isn't honing the new cylinders correctly, changing them won't cure your problem.

[Crash one]

The honing would have to be extremely course and exactly square to the bore to have that effect. The hone would have to be held stationary for some time to produce grooves that bad, requiring incompetence of biblical proportions.

[ShyTorque]

The honing would have to be extremely course and exactly square to the bore to have that effect. The hone would have to be held stationary for some time to produce grooves that bad, requiring incompetence of biblical proportions.

No, I don't think so. The honing angle can be quite critical and ninety degrees isn't the critical angle, it's much less. I always understood that it ought to be 45 degrees and anything shallower is less than ideal. Maybe a misunderstanding like that has caused the problem. But then, I'm just an amateur engine builder who likes to read up the theory, so what would I know?

[noflynomore]

I did post a link (above) regarding the highly technical aspects of honing and ring chatter but from the responses afterwards figured it hadn't been widely read...These last posts confirm my suspicion.

Even if the honing angle is wrong surely it is the same in all four cylinders - or is it? Clearly something is different in that one cylinder that is oiling. Is there any possibility one cylinder was honed at a different time or setting to the others? Maybe the honing angles should be checked?

[Crash one]

I would agree that 45deg is the ideal, but to cause chatter I think they would have to be close to zero. Just my opinion from a practical thinking point of view, I haven't read the theory either. Perhaps someone could explain chattering at, say, 30deg, 20deg? I can understand the oil transfer bit but not chatter.

[piperboy84]

I would agree that 45deg is the ideal, but to cause chatter I think they would have to be close to zero. Just my opinion from a practical thinking point of view, I haven't read the theory either. Perhaps someone could explain chattering at, say, 30deg, 20deg? I can understand the oil transfer bit but not chatter.

All four were done together at the initial tear down inspection, then when the problem surfaced on #1 it was re-honed. The problem persisted so they looked at the crosshatching via a borescope and were satisfied and also said there was no "glazing" visible. Reading the attached article I see this "plateau" issue but am not really understanding it or know if it's relevant to this problem.

[Crash one]

I would agree that 45deg is the ideal, but to cause chatter I think they would have to be close to zero. Just my opinion from a practical thinking point of view, I haven't read the theory either. Perhaps someone could explain chattering at, say, 30deg, 20deg? I can understand the oil transfer bit but not chatter.
Correction: I have read at least a part of the linked theory.
Halfway down page three is a reference to a standard passenger car having what amounts to far wider tolerances.
The average aircraft engine of this type is not a race tuned high performance engine with every ounce of power squeezed out of it. Followed by a complete rebuild after the race. It was developed from an engine designed to drive a farm tractor.

[ShyTorque]

Crash, I don't think the role of the engine makes any difference to the requirement for good piston ring bed-in. The information in the article linked to in this thread echoes good engineering practice.

I just found this alternative link, to advice from a supplier of honing tools: Technical information on using engine hones, flex-hones, ball hones (http://www.enginehones.com/technical.html)
I'd have thought they should know, if anyone does.

But the OP says this isn't the cause of his problem in any case.

[Crash one]

I agree that it is good engineering practice, I'm not advocating anything less.
I am merely suggesting, as you say, that this perfect honing business is not the problem.

Having read that Flexi Hone link, they are merely describing standard practice. After 60 years of crawling in amongst engines and other things engineering, I would have written the same article in the same fashion myself.

[RINKER]

Has anyone looked at the piston ring grooves and The rings themselves to make sure
They are within tolerances and fitted correctly. Most rings have very specific
Beveled edges etc and must be laid right. Last year I managed
And built a 16 ltr Caterpillar diesel on an offshore crane with a Caterpillar
Engineer and I had to correct him on this point. Also are the bores new or refurbed
Have they tried moving the cylinder to a different position to see if the problem
Moves which could suggest crankshaft or crankcase misalignment and would the
Previously good cylinder moved to the bad position replicate the fault.
Is the crankcase,crankshaft New or from the incident engine.
You say they did a borescope inspection. If that was on an assembled engine
That would not show another possibility which is a broken piston ring, quite common.
On a rebuilt engine. This would explain, noise, plug fouling and may only cause
Slight compression loss.
Lots of possibilities.
Regards

[TelsBoy]

Is this the same as piston slap?

[Crash one]

Is this the same as piston slap?

No
Piston slap, as the name implies, is the piston (worn undersize) rocking from side to side as it moves up and down the bore, "slapping" against the bore.

[TelsBoy]

OK, thanks for clarification.

[sycamore]

P-84 it might be worth reading `PelicansPerch` by John Deakin,on engine operation,esp. #78.In fact ,all his articles are worthwile reading on engine handling.

[Progressive]

Given that the problem is oil fouling related and not compression i would be looking at the third (oil control) ring very carefully.
Is the ring installed up the right way?
Is the spring installed correctly behind the ring?
Did the mech score the ring groove or side of the piston when removing/installing the ring? (Oil can bypass the ring down the score mark)
Are the end and side clearances for the ring correct, it is not uncommon for new rings to need the ends adjusted on lycomings.
Is the ring the correct oversize for the cylinder?

[megan]

Just to throw in a little history re ring flutter. From Graham Whites "R-2800"lt was only in the early 1930s that any semblance of good ring design had evolved. Prior to this, aircraft engines and any other engine for that matter, tended to suffer from excessive oil consumption. This was a result of the piston ring’s steam engine ancestry. The two primary functions of piston rings are (1) to seal the piston against the enormous gas pressures generated during the power stroke and (2) to reduce the flow of oil into the combustion chamber to a minimum. Always a difficult design challenge, ring development tended to progress on an empirical basis. The spring tension in a ring is not very important, since the major component of the radial pressure for sealing is provided by gas pressure behind the ring exerting pressure against the cylinder wall. Spring tension, however, does play a more important role in the case of a badly wom cylinder. Side clearance in the piston ring land is a key dimension. Sufficient clearance needs to be provided for to allow gases to flow over the top face of the ring and pressurize it against the cylinder wall. On the other hand excessive clearance will result in hammering of the ring against the lands, resulting in premature failure. This is especially true of the vulnerable top ring land. Early engine designers failed to realize the importance of sufficient land clearance. This resulted in collapsed rings, i.e., the gas pressure would tend to force the ring inwards thus destroying the seal. Sir Harry Ricardo was one of the pioneers to realize this anomaly with a tank engine he developed during World War I. As a quick expedient he had grooves machined into the top faces of the rings to allow the gas pressure to get to the back ofthe ring. Ring face width was another area of controversy. The proponents of a wide ring face argued that there was less chance of the oil film being squeezed out, particularly towards the top of the stroke where boundary layer lubrication exists. This, of course, resulted in less cylinder barrel wear. On the other hand, a wider ring carries more inertia, resulting in a greater tendency to ring flutter. Ring flutter is the phenomenon caused at high piston speeds, typically 2500 feet per minute and higher, when the ring will float off the lower ring land consequently destroying the gas seal. This results in violent blow-by and significant loss of power. For many years this phenomena was thought to be caused by radial vibration of the ring. Paul Dykes, for whom his piston ring is named, demonstrated what really occurred. Under normal circumstances, as the piston rises on the compression stroke, the ring is held, at first by inertia, and later by gas pressure, against the lower ring land. In this way, the full clearance above the ring is available for gas pressure to seal the ring against the cylinder wall. And at the same time the lower land is completely sealed. At some critical piston speed, however, the ring’s inertia will exceed both friction and gas pressure during the compression stroke and allow the ring to float off the lower land. Under these running conditions the ring will lose the gas seal and collapse resulting in the classic case of "ring flutter." The foregoing gives an idea of the idiosyncrasies involved in ring design. Most of it resulted from trial and error. Rolls-Royce ran afoul of ring problems developing the 1931 Schneider trophy "R" racing engine. At one time during this engines development, oil consumption reached an unheard of rate of 112 gallons per hour!

[Crash one]

This thread reminds me of something.
Some years ago when my daughter first got interested in horses, the horse went lame. Although it was still standing up and was being ridden at the time. Although limping a bit.
A supposedly knowledgeable "instructor" said "ruptured Suspensory Ligament". We immediately crapped ourselves of course and thought the worst, until we read up on it.
If there are any vets out there I'm sure I just heard one fall off his chair and spill coffee all over the keyboard.

[piperboy84]

It's been nine long months since I minced the prop
I've lost count of the times it's been back to the shop

They said it was the timing, they said it was the mags
But after every fix the Lycoming ponies ran like old nags

They eyed the pistons, they suspected the rings
But no matter what I couldn't fly my wings

I begged and pleaded with the insurance and the engineer
I hovered over the mechanic so much he suspected I was odd

With no end in sight, hope surrendered to depression
Would I ever get better than low sixties on the compression


It fouled the plugs and burned oil like a bastard.
Thoughts of writing the Maule off as a total disaster

But today a test flight was flown with a prayer for better luck
It finally ran like a dream making me as happy as Larry.

[Crash one]

Nice one Piperboy.
However, what was the problem? Did they solve it or just bury it in expensive replacements?

[cotterpot]

I think he needed to get his rhyming couplet adjusted :)

[piperboy84]

Nice one Piperboy.
However, what was the problem? Did they solve it or just bury it in expensive replacements?

That's exactly what they done, it would appear they got sick of me and took the shotgun approach to troubleshooting

[Crash one]

Did you get the defunct bits back or a bunch of mumbo jumbo krap and sucking of teeth?
Seems a pretty common scenario amongst maintenance outfits, no doubt I'll get hung for saying it, but it looks like they wouldn't recognise a good engineer if she sat on their face and wriggled.