Lycoming piston pin plug failure
 

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.

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....

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.

DAR
 

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.

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

Zulu Alpha
 

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.

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

Alloy in the oil
 

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.

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.

Is this by operators or the rebuilders?

It would be helpful to know what procedure we should follow

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..........................

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

Lycoming general Quality issue
 

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.

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

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?

Lycoming Quality - it's a joke
 

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.

Yet, this cannot be the whole story.

Most engines still do make 2000hrs.

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.

Bob
 

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

Circlips
 

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!