Lycoming piston pin plug failure

[A and C]

Over the past few years I have seen an increasing number of piston pin plug failures on Lycoming engines.

This usualy happens when a ridge forms in the cylinder at the point that the oil control ring reaches BDC, the piston pin plug then gets a little metal shaved off it each time it passes the ridge.

Has this happened to your engine?

If so can you post the following details:-

Type of engine.

Total time the cylinder has run.

Type of flying. (IE trainning, touring aerobatic etc)

Type of oil used.

Manufacturer of Cylinder. (IE Lycoming, ECI etc)

I am trying to see if there is a common thread to these problems.

[Pilot DAR]

Lycoming piston pin plug failures have been around for a long time. In the late 80's through mid 90's, I worked closely with an engine overhaul shop, and investigated a number of these. Though I know longer retain any specific details, the overlying theme is that the original Lycoming parts are comprised of the tubular shaped wrist pin, and the two aluminum plugs which will slid in the ends of the pin. There was an aftermarket wrist pin which had a solid aliminum pin rveted within the steel wrist pin. It worked well.

The aluminum plugs keep the steel wrist pin centered within the cylinder diameter, without damaging the cylinder walls (it's softer). Unfortunately, the original design is lacking, in that the pin wobbles a little up and down with each stroke. The wobbling gets worse and worse, 'till the pin is able to roll over in it's cavity in the piston. When it starts to roll over, nothing stops it, and it can turn whicever way it wants. In variably, it beats it's way out through the piston skirt, and is now floating around in the crankcase. True to Murphy's law, it will go where it can do the most damage, and will find it's way between the case casting, and the head of a valve lifter. When the camshaft closes the lifter, the chunk of plug jams everything, and jams the lifter open (= valve closed). this will really damage the camshaft, and usually break off a part of the head of the lifter, which now bounds around the case itself.

Added to the trauma, is that the high cam in Lycomings (as opposed to the low cam of Continentals, which benefits from the drip oil off the crackshaft) are not quiet as well lubricated, so are even more quickly damaged (not that oil would really have stopped it anyway).

I do have some photos of a few engines we documented, I'll dig them out, and post them. I do not recall any particular set of conditions which caused this condition, it seemd varied across different circumstances. It would take a few hundred hours of running time to happen though.

Your only real means of detection is oil analysis, and noticing way too much aluminum in the oil (knowing that a little is normal). Other than that, you're pulling cylinders to find the condition. The solid wrist pins were the solution. I have not been associated with this problem for many years now, and am not up on the latest developments. I hope that the market forces have made the more durable wrist pins. This is not a condition to be taken lightly. If you think it' happening, get the parts replaced quickly, it will be very costly, and you'll be gliding, if the full damage occurs....

[IO540]

I would expect to find ally in the oil filter - this is always supposed to be cut open at the 50hr replacements.

However I think many MOs don't cut filters open.

And almost nobody does oil analysis.

[A and C]

Thank you for the reply, this latest batch of failures is usualy found when you cut open the filter and find small slices of the piston pin plug in the oil filter.

If you are smart you pull the cylinders off and find the plug that has the problem, it is the ridge that forms at the BDC point of the oil control ring that is the root cause of the problem.

I have now had this happen to three engines that have been under my maintenance control since overhaul, these engines have cylinders from three different manufacturers............. I am trying to find a common thread to the problems.

[Zulu Alpha]

Richard Isenberg at Southend has had a long "discussion " with Lycoming about this. These plugs form an almost airtight seal with the piston. So an increase in temp causes the plug to be pushed out. There are two small holes on the bottom of the piston to relieve this pressure.

They tend to get blocked so the alloy plug is pushed onto the cylinder wall.

Richard fits the gudgeon pins with attached end plugs which are a smaller diameter and says the problem goes away. I think they are made by superior

[A and C]

Thank you for that, another overhaul agency has remarked that the plugs made by Superior seem not to suffer from this problem.

I made no mention of this as I did not want to leed any one into an answer. Has Mr Isenburg made any other comments about factors contributing to this problem.

[Zulu Alpha]

I had a long chat with Richard about this and he persuaded me to change the gudgeon pins and caps. Best to speak with him for the whole 9 yds as it was about 3 yrs ago.

ZA

[Foreplane]

Just found this week.

0-235
About 580 Hours
Mostly training
Orignial fit cylinders on factory overhauled engine

Ad 80 oil
Found in opened oil filter at 50 hour check.

Front two cylinders being removed for inspection....... at the moment!

Also this summer.

0-320
2200 hours
Training and touring
Oringinal fit factory new engine
Ad 80 oil

Also found ferous bits so engine replaced.

[IO540]

I've had some input on this from a highly respectable firm in the USA (one that did my engine in 2008) which reports no issues and suggests that some procedures are not being followed.

[Zulu Alpha]

some procedures are not being followed

Is this by operators or the rebuilders?

It would be helpful to know what procedure we should follow

[A and C]

Thank you all for the posts above.

At the moment the only thing that seems not to be a factor is the oil used, the problems with piston pin plugs are apparent with all types of oil used. So I think that as all the common oils in use in aviation are of a high quality oil type can be ruled out as the sorce of this problem.

I am still looking at the types of piston pin plug that are fitted, there are a number of types, some having a much higher failure rate than others.

More to follow..........................

[N7426G]

Aluminum in the oil filter. Scuff marks on cylinder wall as seen by bore scope.

Type of engine. Lyc 0320 E2D

Total time the cylinder has run. 140 hours

Type of flying. (IE trainning, touring aerobatic etc) Short trips

Type of oil used. Phillips

Manufacturer of Cylinder. ECI

[A and C]

I have now had three sets of O-235 cylinders only make 600 hours before piston pin plug problems, one cylinder set only made 290 hours !

The engine that made 290 hours from OH then has a shock load inspection at 400 hours and the camshaft and followers required replacement.

Another of my engines has now had to be overhauled due to cylinder and cam issues having only run 1300 hours.

So at the moment Lycoming seem to be producing O-235 Cylinders that are good for 600 hours and cams that are good for 1300 hours.

Thirty or so years back when I started in this business you could expect an O235 to run to 2400 hours with one cylinder change at mid life, my only conclusion is that Lycoming have let their quality control slip.

I am now adjusting my having to adjust my prices to reflect the fact that a Lycoming engine is likely to only make half the TBO that they recomend.

[cockney steve]

Forgive me if I'm barking up the wrong tree, but a fully-floating Gudgeon (wrist) -pin strikes me as a primitive bodge-job allowing poor manufacturing tolerances to be accomodated.
No apparent reason comes to mind , why circlips in the piston / press-fit in the piston / floating in piston with clamping at small-end eye could not have been adopted.

The simplest, most elegant, proven and cheapest is the circlip.
Strikes me that It gets rid of the extra reciprocating mass as well....hollow pin can still be a press-fit in pistin, thus ensuring the wear takes place where it should (small-end bearing)......Oh.but wait! the sale of pistons/rings/cylinders would reduce dramatically and the parts-market don't want to lose a captive cash-cow, do they?

Not really surprising thatRotax has made such huge inroads on the GA scene in the last few years, whilst the Lyconsaurus dinosaurs rest on their laurels and take the whizz,

Seen it all before with the British motorcycle industry, followed by the british car industry......we now make better Jap-cars than the Japs , so it's not just poor workmanship,- Management has to show the way and start respecting the fact that ultimately it's the CUSTOMER that pays their wages.


Ahh, feel better for that little rant. :E

[wsmempson]

In the Triumph motor-racing fraternity, where the gudgeon pins where retained by circlips which mounted in a recess within the piston, it was common practice to replace the circlips with PTFE buttons.

Being self lubricating, they never seemed to wear out and they never damaged anything, unlike the circlips which had an unpleasant habit of popping out at high revs and thereby scrapping the engine. I assume nothing so sensible is allowed in the world of certified aero engines?

[Bob Upanddown]

my only conclusion is that Lycoming have let their quality control slip.

Very old news, I think. Most reached that conclusion with the crankshaft failures over 10 years ago starting with SB549, then SB550, SB552........ Nothing has changed.

Similarly, the issue with piston pins has been going on for years and has been reported to Lycoming and regulators in the EU (who have, as usual, done nothing as it is under the FAA's regulatory oversight).

Lycoming could not give a ####. Their customer service is based on the POV that most owners are stuck with Lycoming so they can be treated with contempt.

[peterh337]

Yet, this cannot be the whole story.

Most engines still do make 2000hrs.

There has to be some other factor involved.

[Bob Upanddown]

There has to be some other factor involved.
A reason for reporting to your NAA which should allow the NAA and, if EASA were so enlightened, for EASA to determine a pattern to the failures.
Maybe A&C would like to report his findings to EASA.

[A and C]

We have the CAA in tomorrow for the annual EASA 145 audit, I might raise the topic.

[modelman]

Don't understand either why circlips are't used- the round wire section ones are particularly good as the chamfer on the ends of the gudgeon pin makes them seat even tighter.
Raced/built many high revving bikes,never had one pop out.
The mangles on the front of our planes can't really be classified as high revving at around 2700!

[dieseldo]

Continentals do suffer from the same problem.

We started to get aluminium in our 0-200 oil filter.

For ease we removed the engine and sent it to Richard Isenberg (top man and recommended by me).

If I remember rightly the cause was the pins comming loose in the gudgeon pin and a build up of air pressure due to heat forcing them hard against the cylinder walls.

Running sweet as a daisy ever since and that was quite a few years ago.

[A and C]

I to have talked to Richard Isenburg on this subject but he could offer no theory about the reason for the O-235 cylinder problems that are the root cause of the piston pin plug problems.

This along with the other problems is pointing me towards a lowering of engineering standards at Lycoming.

[peterh337]

The Q to ask is why don't all engines (of that type) suffer from this.

[A and C]

My guess it that the O-235 cylinders are thinner that the others in the range and have a habit of warping, the result of this that a step gets worn at the bottom of the bore by the piston rings, this step bacon slices the piston pin plug.

Strange that Lycoming offer half the warranty on the O-235 cylinders that they offer on the rest of the range.

[cockney steve]

My guess it that the O-235 cylinders are thinner that the others in the range and have a habit of warping,
Warping would not necessarily cause a wear-ridge BUT if, indeed, these cylinders are thinner, they could well be a more ductile cast-iron "brew" than their more sturdy bretheren.....therefore the rings, in the absence of extra oil-supply could well wear the bore unevenly from top to bottom. It's normal to get a wear-ridge at the top(where the ring stops-top of skirt usually goes a fair bit higher) but the lower-ridge is usually not significantly developed before the upper one dictates a rebore/sleeve/new barrel (dependent on procedure for specific engine.)

Either way, sounds like the design is NOT optimised for longevity and i'd suspect the short-runs/intermittent use nature of GA does it no favours either.

A piston-engine will do loads more if given long stretches at working-temperature. as opposed to "short hops" the cold-start cycle (especially if it's been stood a week and all the internal oil has drained down) causes a disproportionate amount of the wear.

my diagnosis:- poor design, inferior materials.....a good cash-generator for the spares sales business.

cynic?...What! Moi?:E

[A and C]

The ridge is always at the bottom, not the top.

I am starting to think that You are correct about the quality of parts, thirty years back it was common for an O-235 to make TBO + 20% with a top end overhaul at half life.

The worst I have had is piston pin plugs at 290 hours and impending camshaft failure at 400 hours ( found at a shock load inspection).

Have Lycoming now found a very good income stream by producing poor quality parts ? I am not quite as cynical as you and think that the quality has gone down due to the pressure from the environmental legislation as some of the processes required are not very environmentally friendly. Add the pressure to keep costs down from the PMA parts suppliers and you have great pressure to go down market.

It has been demonstrated to me that Lycoming genuine parts no longer show any advantage over PMA items but are more expensive, I have run my business in the belief that quality is the best policy and I am more than happy to pay a premium for reliability but if I am not getting this reliability then Lycoming are driving me into the arms of the PMA market.

An own goal by Lycoming I think.

[neilmurg]

I am looking at an aircraft with this exact problem it is on the front two cylinders, which were replaced ~475 hours ago with genuine Lycoming cylinders. The cylinders replaced had ALSO exhibited the same problem after ~1075 hours. Those cylinders were Superior Millennium parts...

There is a theory that it may be exacerbated by excessive cooling on the front face of the front pots. I suspect it is some combination of inadequate lubrication, inadequately hardened cylinder wall and a dynamic which is forcing the plug against the cylinder wall, where it has no right to be.

It's very depressing that it has recurred on the replacement parts, where do you go from here?

Is North of barlu in the Pacific above Oz?

[A and C]

Barlu was an airways intersection near Cherbourg but I'd disappeared about twenty years back to be replaced by the nearby Akiki.

[Robin400]

I was told forty years ago this problem is caused by not allowing sufficient time at low rpm before full power is set.
The aluminum piston expands losing contact with the pin allowing it to slide about in the piston. Some time later the pin warms up and tightens in the piston to one side causing cap wear.

[A and C]

Three of my aircraft are based at a large airfield, it is just not posable to get the aircraft from the parking position to the runway without getting the engine warm enough for tale off.

I don't discount what you say but it is not relevant in my case.

I now base my business on Lycoming engines requiring overhaul at half TBO as this is all that the engines has demonstrated to me that they are able to achive.

[27/09]

I've seen this problem on O-235s fitted to C 152s. At the time we had several piston plugs "fail". Apparently there was never a problem with the O-235s fitted to the PA38. This led us down the path of wondering why a problem with the C152 but not the PA38, essentially same engine in both.

The PA38 never had an oil cooler fitted whereas the C152 did. Blanking of the oil cooler on the C152 cured the problem if I recall correctly.

[peterh337]

As I wrote in this thread a long time ago, this issue is not common in the USA (whose engine population is some 10x bigger) and appears to be due to "something" peculiar to UK engine rebuilding practices.

[27/09]

As I wrote in this thread a long time ago, this issue is not common in the USA (whose engine population is some 10x bigger) and appears to be due to "something" peculiar to UK engine rebuilding practices.

I'm not sure I agree.

There have been problems outside of the UK and with rebuild shops that have many years experience. The problem started all of a sudden, I suspect there was a change in spec for the plugs or some related part which precipitated the problem.

Lycoming outsourced a lot of their parts manufacturing and as a result lost direct control of the QA process. Remember the issues with the crankshafts a while back.

[A and C]

The first engine that had exhibited this problem was a Lycoming factory rebuild, the others were overhauled in the UK.

27/09

It is not a piston pin plug problem but one of cylinder becoming ridged at the lower end of the area swept by the piston rings, as the piston pin plugs pass over this step they have small chips removed this becomes very evident when the oil filter is cut open at maintenance checks.

The oil cooler thing mentioned above has a ring of truth about it as the lowest time engine that had this problem had it appear after just under 300 hours, the aircraft had been doing a lot of night training flights and the OAT was some times -15C or below.

The only positive thing to come out of this is that the customer support from the UK Lycoming agents has been very good, they too have suggested that this might be an over cooling problem.

[27/09]

A and C Note I said piston plug or other related part, I was disputing overhaul techniques being the problem and suggesting a parts issue was the cause.

I agree probably not the piston plug, more likely the composition of the cylinders or the rings.

I'll bet the cylinders that had the lip causing the plug wear were the front two.

[A and C]

Usually the steps are worse on the front cylinders but all usually have a step when the problem occurs.