Ring Chatter (or slap)
Avoid imitations
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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
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.
I just found this alternative link, to advice from a supplier of honing tools: Technical information on using engine hones, flex-hones, ball hones
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.
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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.
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.
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
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
Last edited by RINKER; 13th Feb 2017 at 22:39.
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Piston problems
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?
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?
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!
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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.
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.
Thread Starter
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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.
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.
Thread Starter
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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.
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.
