Lycoming Connecting Rod Bushing AD 2024-21-02

[MikeOH]

The more times I read this AD, the more confused I become!

I assume the issue is with the bronze bushings, themselves.  So, were any shipped outside the factory?  The AD provides PNs for both bushing and connecting rods assemblies with the suspect bushings.  You'd think it would be more than just the engines assembled during the stated time period.  Did the parts ONLY get shipped out during the same period?  Seems unlikely, but who knows?  Finally, given this goes back to 1/30/2009, how long have the suspect bushings been in service?  So, 15 years later we're now told we must look for bronze chips for a while?

 

[PT20J]

10 minutes ago, EricJ said:

That was my first read, that it intends to address engines shipped from Lycoming.   However, it doesn't say that explicitly, and leaves a lot to interpretation.   It could be read that it was intended to include anything assembled in the field during the specified times with the listed part numbers.   I don't know why the assembly date would drive, though, as one would think the batch of the intalled part would be more important.

I think the bottom line is that it is just a very poorly written AD.  Regardless of how the AD is disposed in your logbook, I think it'll be worthwhile to pay attention to your filter media for bronze chips for a while. 

This issue has been known to Lycoming for some time. The latest "ship date" listed in the AD (I'm still not 100% clear if these dates only apply to entire engines or also to the connecting rod assemblies) is Feb 2017. The Lycoming SB 480F Oil Servicing, Metallic Solids Identification After Oil Servicing, and Associated Corrective Action was updated 5/25/17. Lycoming SB 630A Connecting Rod Bushing Inspection After Cylinder Removal was updated 6/17/17. Evidently the bushings can loosen in service and either rotate in the rod or move out of the rod bore. Either movement can apparently cause them to wear and eventually fail. But apparently there have been some catastrophic failures leading to the AD. Based on the AD language, Lycoming and the FAA seem to believe that normal interval inspections of the filter media and suction screen will indicate an issue before it causes a failure. So, it begs the question: Where the filters in the engines that failed not being inspected?

[DCarlton]

Will the FAA respond to questions?  How many engines have failed?  How many hours were on the engines that failed?  What is the root cause?  Was the wrong material used; were the bushings not manufactured to correct tolerances etc?  How did they isolate the production lots in question?  Do the bushings degrade suddenly or fail slowly over a long period (years)?  Explain why a periodic oil inspection is sufficient to catch degradation early enough to prevent failure etc?  How do you adequately inspect a connecting rod bushing in one work hour?  

[MikeOH]

Are the piston pins full floating? Is there an oil hole in the bushing, fed from the rod journal, such that rotation of the bushing would cut off the oil supply, or are they splash oiled (press fit pin)?

[DCarlton]

10 hours ago, MikeOH said:

Are the piston pins full floating? Is there an oil hole in the bushing, fed from the rod journal, such that rotation of the bushing would cut off the oil supply, or are they splash oiled (press fit pin)?

I was wondering that too.  I’ve had similar main bearing issues with a boat engine.  Added to the list.  Gonna email the FAA.  Update:  Sent the FAA POC several questions.  Will advise if I see a reply; guessing they are swamped.  

[jetdriven]

The piston pins are full floating. The bushing is pressed to the end of the connecting rod and it’s basically part of the rod. The pin fits through the piston and the small end of the rod and the other side of the piston by hand. There is a bushing that goes over each end of the piston pin from the outside of the piston. . Unless you’re talking about superior pistons, and pins which have an integrated button on the end of the piston pin, which is not  interchangeable.  Those must be replaced in opposing pairs.  
 

[AndreiC]

Here is a question for the APs around here. Is it possible to replace the bushings without taking the connecting rod out of the engine? My understanding of the mechanical process involved makes me doubt it is possible, right? Then how do you replace all four bushings in 4.5 hours, per the FAA? I would think the job requires splitting the case, which is (my guess) closer to 40 hours, even without counting the cost of taking the engine off the plane and reinstalling it... I really wonder how the FAA comes up with those numbers.

[N201MKTurbo]

1 hour ago, AndreiC said:

Here is a question for the APs around here. Is it possible to replace the bushings without taking the connecting rod out of the engine? My understanding of the mechanical process involved makes me doubt it is possible, right? Then how do you replace all four bushings in 4.5 hours, per the FAA? I would think the job requires splitting the case, which is (my guess) closer to 40 hours, even without counting the cost of taking the engine off the plane and reinstalling it... I really wonder how the FAA comes up with those numbers.

It is normally done in an arbor press. It is possible to make a device to do it on the plane, but it would be expensive to make. I think the normal way to do it would be to take the rod off the engine, change the bushing and put the rod back on. It can be done if you take all the cylinders off. You will need to buy new rod bolts and nuts, they are about $100 each and you need two for each rod.

[DCarlton]

2 hours ago, AndreiC said:

Here is a question for the APs around here. Is it possible to replace the bushings without taking the connecting rod out of the engine? My understanding of the mechanical process involved makes me doubt it is possible, right? Then how do you replace all four bushings in 4.5 hours, per the FAA? I would think the job requires splitting the case, which is (my guess) closer to 40 hours, even without counting the cost of taking the engine off the plane and reinstalling it... I really wonder how the FAA comes up with those numbers.

And how do you know you're replacing the bushing with better bushings with adequate QA if you don't know what's wrong with the ones you're taking out.  No details provided (although I haven't read the LYC bulletins yet).  Maybe it's there... 

[DCarlton]

2 hours ago, jetdriven said:

The piston pins are full floating. The bushing is pressed to the end of the connecting rod and it’s basically part of the rod. The pin fits through the piston and the small end of the rod and the other side of the piston by hand. There is a bushing that goes over each end of the piston pin from the outside of the piston. . Unless you’re talking about superior pistons, and pins which have an integrated button on the end of the piston pin, which is not  interchangeable.  Those must be replaced in opposing pairs.  
 

So... which bushing is failing?  The one pressed into the rod that's part of the rod or the ones that go over the piston pin?  

[AndreiC]

24 minutes ago, DCarlton said:

And how do you know you're replacing the bushing with better bushings with adequate QA if you don't know what's wrong with the ones you're taking out.  No details provided (although I haven't read the LYC bulletins yet).  Maybe it's there... 

The summary of the Lycoming bulletin is in three steps:

1) If you don't see a certain amount of bronze in your oil filter or your oil suction screen (you need to check both at each oil change), do nothing. This can be done by a registered pilot, no need for an A&P.

2) If you do see the amount listed (quite high -- 6 bronze chips, or 3 bronze chips and 3 aluminum chips; here chip means as far as I understand it between 1/16" and 3/16"), or every time you pull a cylinder, then you need to inspect the bushing(s). This involves pulling cylinders. The two things to check are if the bushing has moved out of the rod (no longer aligned with the rod) or if it has turned in the rod. If none of these have happened, again, do nothing.

3) If you see a bad bushing, it needs to be replaced. Or you can choose to replace all four preventively in order to terminate the repetitive AD. At overhaul all bushings must be replaced. 

As far as I understand it, there must have been a batch of bad bushings during the period discussed, but I do not understand from the text of the AD if these were only used in the Lycoming factory and other overhaulers never saw them, or if they were in wide circulation and anyone who has had had their rods overhauled as part of a major or some other work on the rods is exposed to the risk of having one of the bad guys. 

The open questions, for me:

a) As above, does this only apply to rods that came from the factory, or rods that had bushings installed that were provided by the factory (are there other bushing providers?), or ??

b) Is my above interpretation of the SB correct, in that you need to see a large amount of bronze to act, or is what the AD says "any amount of bronze particulate" the trigger for an inspection?

c) How many engine failures were there related to this, and how come the large amounts of bronze that should have been seen in the oil filter were not caught? In other words, why should we believe it is safe to operate with a potentially bad bushing thinking we'd catch it at a 50 hour oil change?

[N201MKTurbo]

9 minutes ago, DCarlton said:

So... which bushing is failing?  The one pressed into the rod that's part of the rod or the ones that go over the piston pin?  

It would be the one in the rod. The ones that are on the ends of the pin are aluminum.

 

[N201MKTurbo]

3 minutes ago, AndreiC said:

The summary of the Lycoming bulletin is in three steps:

1) If you don't see a certain amount of bronze in your oil filter or your oil suction screen (you need to check both at each oil change), do nothing. This can be done by a registered pilot, no need for an A&P.

2) If you do see the amount listed (quite high -- 6 bronze chips, or 3 bronze chips and 3 aluminum chips; here chip means as far as I understand it between 1/16" and 3/16"), or every time you pull a cylinder, then you need to inspect the bushing(s). This involves pulling cylinders. The two things to check are if the bushing has moved out of the rod (no longer aligned with the rod) or if it has turned in the rod. If none of these have happened, again, do nothing.

3) If you see a bad bushing, it needs to be replaced. Or you can choose to replace all four preventively in order to terminate the repetitive AD. At overhaul all bushings must be replaced. 

As far as I understand it, there must have been a batch of bad bushings during the period discussed, but I do not understand from the text of the AD if these were only used in the Lycoming factory and other overhaulers never saw them, or if they were in wide circulation and anyone who has had had their rods overhauled as part of a major or some other work on the rods is exposed to the risk of having one of the bad guys. 

The open questions, for me:

a) As above, does this only apply to rods that came from the factory, or rods that had bushings installed that were provided by the factory (are there other bushing providers?), or ??

b) Is my above interpretation of the SB correct, in that you need to see a large amount of bronze to act, or is what the AD says "any amount of bronze particulate" the trigger for an inspection?

c) How many engine failures were there related to this, and how come the large amounts of bronze that should have been seen in the oil filter were not caught? In other words, why should we believe it is safe to operate with a potentially bad bushing thinking we'd catch it at a 50 hour oil change?

I believe Superior also makes these bushings.

[Greg Ellis]

So, a curious question….I had to have my engine taken apart in 2013 after problems with an earlier overhaul.  This work was done by a major engine shop.  They mention nothing in the log entry of part numbers for connecting rod bushings or assembly.  The only thing mentioned is that the engine was reassembled with new rod and main bearings, new rod bolts and nuts.  No part numbers listed other than for the crankshaft, camshaft, pistons, piston pins and piston rings and other parts not related to this.  To find out if I have the affected parts would I have to contact the engine shop?  I’m thinking yes.

[N201MKTurbo]

SL13923A Superior Air Parts Aircraft Products BUSHING CONNECTING ROD - Part Number: SL13923A - [IN STOCK]

01K28983 Lycoming BUSHING CONNECTING ROD UPPER - Part Number: 01K28983

LW-13923 BUSHING-CONNECTING ROD-UPPER(2 - Part Number: LW-13923

AEL13923 Continental Bushing Connecting Rod - Part Number: AEL13923 - [IN STOCK]

 

It looks like Lycoming, Continental and Superior make this bushing.

[N201MKTurbo]

1 minute ago, Greg Ellis said:

So, a curious question….I had to have my engine taken apart in 2013 after problems with an earlier overhaul.  This work was done by a major engine shop.  They mention nothing in the log entry of part numbers for connecting rod bushings or assembly.  The only thing mentioned is that the engine was reassembled with new rod and main bearings, new rod bolts and nuts.  No part numbers listed other than for the crankshaft, camshaft, pistons, piston pins and piston rings and other parts not related to this.  To find out if I have the affected parts would I have to contact the engine shop?  I’m thinking yes.

That bushing wouldn't normally be changed during a repair like you mentioned.

[DCarlton]

14 minutes ago, AndreiC said:

The summary of the Lycoming bulletin is in three steps:

1) If you don't see a certain amount of bronze in your oil filter or your oil suction screen (you need to check both at each oil change), do nothing. This can be done by a registered pilot, no need for an A&P.

2) If you do see the amount listed (quite high -- 6 bronze chips, or 3 bronze chips and 3 aluminum chips; here chip means as far as I understand it between 1/16" and 3/16"), or every time you pull a cylinder, then you need to inspect the bushing(s). This involves pulling cylinders. The two things to check are if the bushing has moved out of the rod (no longer aligned with the rod) or if it has turned in the rod. If none of these have happened, again, do nothing.

3) If you see a bad bushing, it needs to be replaced. Or you can choose to replace all four preventively in order to terminate the repetitive AD. At overhaul all bushings must be replaced. 

As far as I understand it, there must have been a batch of bad bushings during the period discussed, but I do not understand from the text of the AD if these were only used in the Lycoming factory and other overhaulers never saw them, or if they were in wide circulation and anyone who has had had their rods overhauled as part of a major or some other work on the rods is exposed to the risk of having one of the bad guys. 

The open questions, for me:

a) As above, does this only apply to rods that came from the factory, or rods that had bushings installed that were provided by the factory (are there other bushing providers?), or ??

b) Is my above interpretation of the SB correct, in that you need to see a large amount of bronze to act, or is what the AD says "any amount of bronze particulate" the trigger for an inspection?

c) How many engine failures were there related to this, and how come the large amounts of bronze that should have been seen in the oil filter were not caught? In other words, why should we believe it is safe to operate with a potentially bad bushing thinking we'd catch it at a 50 hour oil change?

Great questions but I'd still like to know why the bushing were "bad".  Wrong alloy?  Not machined to correct tolerances?  Why wasn't this caught during QA?  How did they confidently isolate the production lots in question?  What steps have been taken to make sure the new bushing don't have any QA issues?  To manage this issue the FAA has to know the answers to these types of questions, otherwise, they're shooting from the hip.  I wouldn't want to crack open a good engine at significant cost without more details.  Guessing there's a detailed failure analysis report somewhere.  I asked for it; no idea if I'll see a response.  

[N201MKTurbo]

FYI

https://www.lycoming.com/sites/default/files/attachments/SI1575_New_Conecting_Rod_Bushing.pdf

[ArtVandelay]

So, a curious question….I had to have my engine taken apart in 2013 after problems with an earlier overhaul.  This work was done by a major engine shop.  They mention nothing in the log entry of part numbers for connecting rod bushings or assembly.  The only thing mentioned is that the engine was reassembled with new rod and main bearings, new rod bolts and nuts.  No part numbers listed other than for the crankshaft, camshaft, pistons, piston pins and piston rings and other parts not related to this.  To find out if I have the affected parts would I have to contact the engine shop?  I’m thinking yes.

The log entry may not have this much detail, check other paperwork they gave you.
This is where I found it in my case.

[N201MKTurbo]

Most shops are pretty good at charging you for every last piece part and service. I think you can assume if the bushing was not listed, it wasn't changed.

[AndreiC]

I found out more interesting information. There was a previous AD about this same exact problem, but it affected a much smaller number of engines. I am talking about AD 2017-16-11 and the relevant Lycoming Mandatory Service Bulletin (MSB) 632B. It explicitly lists a long list of engines and specific serial numbers (not even a range, specific numbers), as well as connecting rods and bushings shipped from Lycoming in a very narrow range of dates (about 1 year, sometimes between 2015 and 2017 depending on the specific rods). It also gives much more explicit procedures to test for when the bushings are bad, and how to replace bad bushings (as mentioned, this involves removing the connecting rods from the engine).

What I do not understand now is what made the FAA expand the range of dates dramatically (so as now to cover a decade or more) and without specifics on what bushings were bad. 

According to the initial AD from 2017, there had been 5 uncontained engine failures that were attributed to bad bushings.

[DCarlton]

Just checked my engine logs.  My engine overhaul was signed off in July 2016.  The LW-13923 bushing were replaced during overhaul.  The FAA has a concern about bushings shipped up until 11/17/2015.  So now I have to wonder whether the overhaul shop used up the 2015 bushings they had on the shelf before they started my overhaul.  I may have squeaked by..... or not.  Gonna email the shop and see if they keep those sort of records (when parts were received).  I'm planning to start checking for particulates and doing oil analyses anyway just to feel "better".  

[MikeOH]

32 minutes ago, N201MKTurbo said:

FYI

https://www.lycoming.com/sites/default/files/attachments/SI1575_New_Conecting_Rod_Bushing.pdf

THAT is very troubling. They created a brand new part to replace the LW-13923 part used since who knows when.
"The connecting rod bushing P/N 01K28983 will be the only bushing installed in connecting rods, in engines, or available as spares from Lycoming Engines once inventory of connecting rod bushing P/N LW-13923 is depleted."

8 minutes ago, AndreiC said:

What I do not understand now is what made the FAA expand the range of dates dramatically (so as now to cover a decade or more) and without specifics on what bushings were bad. 

I'm beginning to think Lycoming lost control of their QC, specifically traceability; I think the LW-13923 part has been around forever and something went wrong in production and they have only the vaguest idea of when!  When you read the SI that @N201MKTurbo posted it seems they just want to eliminate any confusion as to whether a given LW-13923 part is suspect, or not.

[ArtVandelay]

Just checked my engine logs.  My engine overhaul was signed off in July 2016.  The LW-13923 bushing were replaced during overhaul.  The FAA has a concern about bushings shipped up until 11/17/2015.  So now I have to wonder whether the overhaul shop used up the 2015 bushings they had on the shelf before they started my overhaul.  I may have squeaked by..... or not.  Gonna email the shop and see if they keep those sort of records (when parts were received).  I'm planning to start checking for particulates and doing oil analyses anyway just to feel "better".  

I would be surprised if engine shops, even the big ones, ordered any parts prior to an overhaul, there’s just too much variation and ADs not to order it when it’s required. Id bet an adult beverage your parts were ordered after the deposit was made. Find that date and I would use it.

[Greg Ellis]

1 hour ago, ArtVandelay said:

The log entry may not have this much detail, check other paperwork they gave you.
This is where I found it in my case.

I found in the paperwork the part number AEL-11750-S.  That is different than the Lycoming part number LW-11750.  For all you smarter than me folks…would my part with that part number still fall under the AD?