Lycoming Connecting Rod Bushing AD 2024-21-02

[PT20J]

32 minutes ago, DCarlton said:

They had to describe the "defect" somehow.  Their words could mean anything without more details (I've written DOD failure analysis reports choosing every word carefully).  They're about to gather a lot of data with 16,000 recurring oil filter inspections.  Hopefully they won't need to expand the compliance requirements described in the first AD to cover all 16,000 engines.  That would be a huge blow to GA.  I certainly won't get an answer if Mike Busch didn't but I'm going to ask whether there is any difference in first smaller population of bushings vs the expanded population.  I'll bet every engine shop in the country is asking the same question.  They deserve a detailed answer.  

The way I read the new AD is that Lycoming came to realize that the non-conforming bushings were used in additional connecting rod part numbers not listed in the original AD. I don't know what made them non-conforming. It seems likely that they were undersize because they are press fit and the issue is that they come loose. Lycoming did release a new bushing design subsequently, but I doubt that has anything to due with this problem. The description of the new bushings reads more like a manufacturing process improvement since they don't need burnishing. 

[DCarlton]

The FAA just responded to my inquiry.  I was told I'd need to fill out a Freedom Of Information Act Request that would be reviewed to determine if any information can be disclosed due to the proprietary nature of the issue.  

I responded by asking a few more general questions regarding the two populations of bushings.  

Update.  According to the FAA POC, the failure mode for the two populations of bushings addressed by the two ADs appears similar.  

[PT20J]

I received confirmation from Lycoming that an engine assembled by Lycoming that contains an affected connecting rod assembly is only subject to the AD if the engine ship date falls within the connecting rod assembly date range listed in the AD.

Ship dates for Lycoming assembled engines can be found here https://www.lycoming.com/core-history-search

This, of course, doesn't help with engines assembled outside Lycoming. That will require some research and hopefully the assembler saved the packing slips for the parts with the ship dates.

My Lycoming field rep sent me the attached letter.

Response to Inquiry - AD 2024-10-02_FINAL.pdf

 

[DCarlton]

55 minutes ago, PT20J said:

This, of course, doesn't help with engines assembled outside Lycoming. That will require some research and hopefully the assembler saved the packing slips for the parts with the ship dates.

 

 And if you don't have the Lyc ship dates (or they've been disposed of after five years), you may have a practical choice to make.  Recurring oil inspections for metallic solids or a bushing press out test for ~ $4500 (for bushings shipped between Nov 15 and Nov 16).  

[A64Pilot]

41 minutes ago, DCarlton said:

 And if you don't have the Lyc ship dates (or they've been disposed of after five years), you may have a practical choice to make.  Recurring oil inspections for metallic solids or a bushing press out test for ~ $4500 (for bushings shipped between Nov 15 and Nov 16).  

Isn’t the recurring oil inspections not oil but oil filter? It did include screens etc., my read is that was for non oil filter equipped engines, and suction screens are really rock catchers, the kind of wear particle that would come off of a bushing would surely flow thru a suction screen but be caught in the paper filter pleats or maybe in a filter screen.

Doesn’t it correspond with the normal oil change interval? Aren’t we supposed to be cutting filters open and inspecting at every filter change anyway?

Amazon has filter cutters as cheap as $18 for those that may not have one. It’s a ten minute task, personally I let a filter drain overnight before I cut but there is no need to.

If I knew I had a non compliant engine I’d test all the bushings and unless it was a perfect cylinder I’d re-ring it or have the cylinder IRAN if it’s old and getting tired since I had it off.

But if it was just possible that I may have a non compliant engine but no way to know short of disassembly I’d likely fly it and watch it, but I certainly would understand if anyone said nope only way to be sure is test them.  

Expense wise I wont argue because I don’t know, but I doubt $4,500,  if it’s a good engine it’s very few parts. Parts would come in if you wanted to refresh the cyl while your there. I could do it on a 4 cyl in a long day, but probably two as I’m old now and don’t work as hard as I used to.Longer of course if we are talking rings or going to the engine shop for valves etc. Of course then you could easily get to $4,500 I guess.

[DCarlton]

1 hour ago, A64Pilot said:

Isn’t the recurring oil inspections not oil but oil filter? It did include screens etc., my read is that was for non oil filter equipped engines, and suction screens are really rock catchers, the kind of wear particle that would come off of a bushing would surely flow thru a suction screen but be caught in the paper filter pleats or maybe in a filter screen.

Doesn’t it correspond with the normal oil change interval? Aren’t we supposed to be cutting filters open and inspecting at every filter change anyway?

Amazon has filter cutters as cheap as $18 for those that may not have one. It’s a ten minute task, personally I let a filter drain overnight before I cut but there is no need to.

If I knew I had a non compliant engine I’d test all the bushings and unless it was a perfect cylinder I’d re-ring it or have the cylinder IRAN if it’s old and getting tired since I had it off.

But if it was just possible that I may have a non compliant engine but no way to know short of disassembly I’d likely fly it and watch it, but I certainly would understand if anyone said nope only way to be sure is test them.  

Expense wise I wont argue because I don’t know, but I doubt $4,500,  if it’s a good engine it’s very few parts. Parts would come in if you wanted to refresh the cyl while your there. I could do it on a 4 cyl in a long day, but probably two as I’m old now and don’t work as hard as I used to.Longer of course if we are talking rings or going to the engine shop for valves etc. Of course then you could easily get to $4,500 I guess.

Your 5th para is exactly what I was trying to suggest.  And when I said oil inspections I was being too brief and not specific enough; best to read the SB (I'll be looking at whatever I can for particles and probably sending the oil off for analysis too).  Regarding your 6th para; I asked for an estimate from a reputable trusted builder.  In CA it's $4500 to remove four cylinders and perform the press out test.  Compare that to the FAA estimates.  Sorry for begin too brief but Mooneyspace kept bombing; said too many users were logged in or something like that.  Again, I'm no expert mechanic; just a retired DOD engineer / owner with time enough to investigate this issue myself and read the documents.  

[PT20J]

Apparently the bad bushings can shed chunks and that's the reason for including inspection of the suction screen in the AD.

The original 2017 AD required removing the cylinders to test the bushings for fit. It was simple to determine if you needed to comply if you had a Lycoming-assembled (new, rebuilt, overhauled) engine because all the affected serial numbers were listed. If new rods had been installed in the field, it wasn't so simple because the bad rods were identified only by the date they were shipped from Lycoming. So, whoever installed them would have to have kept records showing when they were shipped.

The 2024 AD doesn't list affected Lycoming-assembled engine serial numbers but it is easy to get the engine ship date from Lycoming and determine if the AD applies. But, again, it's harder to tell with field-assembled engines. 

The 2024 AD isn't difficult to comply with except for the fact that the suction screen is a bit of a pain to get to and many don't inspect it at every oil change. Personally, I have found that the screen gets easier to remove and safety wire (the hardest part) the more times I do it.

[MikeOH]

Just a small/fine point in the 2017 AD: the cylinder does NOT have to be completely disassembled in order to perform the bushing test.  The SB632B shows the piston and rings remaining in the cylinder with just the pin exposed:

 

[Pinecone]

13 hours ago, A64Pilot said:

Expense wise I wont argue because I don’t know, but I doubt $4,500,  if it’s a good engine it’s very few parts. Parts would come in if you wanted to refresh the cyl while your there. I could do it on a 4 cyl in a long day, but probably two as I’m old now and don’t work as hard as I used to.Longer of course if we are talking rings or going to the engine shop for valves etc. Of course then you could easily get to $4,500 I guess.

It is not the cost of the parts, but the cost of removing the baffling, intake, exhaust and all 4 cylinders, removing the pistons from the rods, doing the test and putting everything back together.

[1980Mooney]

50 minutes ago, Pinecone said:

It is not the cost of the parts, but the cost of removing the baffling, intake, exhaust and all 4 cylinders, removing the pistons from the rods, doing the test and putting everything back together.

Also when you remove exhaust hardware that has not been removed in a long time, you may find more problems that require more work - slip joints, flanges, - or corrosion may conspire to induce problems like breaking a stud.

[AndreiC]

Here is some more information after talking to live people:

-- Lycoming technical support said that they agree that the AD is poorly phrased, in the sense that it appears to at the same time say that "any bronze particulates" should trigger a bushing inspection, but at the same time points you to the SB 480F which says that unless you find relatively large "chips" of bronze you can continue to monitor the situation. According to the tech person the only reason Lycoming asked the FAA to create this AD was to force people to be serious about looking at the oil filters and suction screens at each oil change (he said "you wouldn't believe how many mechanics out there do not follow these recommendations"). When asked how many engines failed due to bushings coming apart, he said he did not know. When I pressed and asked if it is more like 3 or like 300, he said he can tell me it's not 300.

But, perhaps as a CYA move, he said that the way he reads the AD as phrased is that if you find even one tiny bronze particle in your oil filter, you are required to pull cylinders and check the bushings. And then, say, you fly it 50 hours, find another tiny bronze particle, you do it again. And so on. Love the FAA and their imprecise wording.

-- I also talked to the final A/W inspector at Penn Yan, so a guy with a lot of experience. He said quite clearly that you should follow the guidance of the SB480F, and look for chips (>1/16" pieces) in the oil filter and suction screen. You don't find these, and maybe find a few tiny flakes, continue to operate as normal, per the SB. He also said that they did quite a few of the inspections required by the earlier 2017 AD, and only found 4-5 bushings that moved and needed to be replaced. He was not aware of any specific engines that actually failed because of moving bushings. So he was firmly recommending just watching the oil filter and the suction screen and be on your merry way.

BTW, I do have the affected bushings, it was confirmed that when my engine was O/H-ed they put in Lycoming LW-13923 with a ship date of 08/2012, so smack in the middle of the affected range.

[DCarlton]

1 hour ago, AndreiC said:

Here is some more information after talking to live people:

-- Lycoming technical support said that they agree that the AD is poorly phrased, in the sense that it appears to at the same time say that "any bronze particulates" should trigger a bushing inspection, but at the same time points you to the SB 480F which says that unless you find relatively large "chips" of bronze you can continue to monitor the situation. According to the tech person the only reason Lycoming asked the FAA to create this AD was to force people to be serious about looking at the oil filters and suction screens at each oil change (he said "you wouldn't believe how many mechanics out there do not follow these recommendations"). When asked how many engines failed due to bushings coming apart, he said he did not know. When I pressed and asked if it is more like 3 or like 300, he said he can tell me it's not 300.

But, perhaps as a CYA move, he said that the way he reads the AD as phrased is that if you find even one tiny bronze particle in your oil filter, you are required to pull cylinders and check the bushings. And then, say, you fly it 50 hours, find another tiny bronze particle, you do it again. And so on. Love the FAA and their imprecise wording.

-- I also talked to the final A/W inspector at Penn Yan, so a guy with a lot of experience. He said quite clearly that you should follow the guidance of the SB480F, and look for chips (>1/16" pieces) in the oil filter and suction screen. You don't find these, and maybe find a few tiny flakes, continue to operate as normal, per the SB. He also said that they did quite a few of the inspections required by the earlier 2017 AD, and only found 4-5 bushings that moved and needed to be replaced. He was not aware of any specific engines that actually failed because of moving bushings. So he was firmly recommending just watching the oil filter and the suction screen and be on your merry way.

BTW, I do have the affected bushings, it was confirmed that when my engine was O/H-ed they put in Lycoming LW-13923 with a ship date of 08/2012, so smack in the middle of the affected range.

Would really like to hear Lycomings thoughts on why the 2017 and 2024 ADs have different compliance requirements for the same P/N, particularly IF the defect is the same for the two populations of bushings.  

{Note:  I was told by a reputable builder they've seen bushing move as well but so far not enough to make metal; I was also told some of the defective bushings were identified and rejected because they were too easy to hand press into the rod; I have a bit more gut confidence since my bushings were hand pressed into the rod.}

[PT20J]

The way I read  SB 480F Table 3 it’s required to remove cylinders to inspect the connecting rod  bushings if any bronze chips are found in the suction screen, or more than 5 bronze chips are found in the filter, or more than three bronze chips and more than three aluminum chips are found in the filter. 

[MikeOH]

Refresh my memory.  What is the definition of a 'chip' vs. ,say, 'particles'?

[PT20J]

2 hours ago, MikeOH said:

Refresh my memory.  What is the definition of a 'chip' vs. ,say, 'particles'?

From SB 480F, chunks are 3/16” or greater; chips are smaller.

[DCarlton]

3 hours ago, PT20J said:

The way I read  SB 480F Table 3 it’s required to remove cylinders to inspect the connecting rod  bushings if any bronze chips are found in the suction screen, or more than 5 bronze chips are found in the filter, or more than three bronze chips and more than three aluminum chips are found in the filter. 

Any idea if there are any other bronze wear items other than the small end rod bushings? 

[AndreiC]

33 minutes ago, PT20J said:

From SB 480F, chunks are 3/16” or greater; chips are smaller.

My reading of the SB480F is that chunks are 3/16" or greater, indeed, but chips are greater than 1/16". Their distinction seems to be into the three categories "chunks", "chips" and "small metallic particles".  For example they say "Use non-metallic tweezers or a pick to sort chunks, chips, and particles that look different." Or they say "Yet metallic particles can be small dust-size particulates - that is where quantity becomes more of the issue in this case." 

Also Table 3 states that "1 to 9 pieces of metal (1/16 in. (1.2 mm)) diameter or less)" is fine and you should continue to operate the engine to the next scheduled oil change. So I assume such pieces are not chips.

[AndreiC]

2 minutes ago, DCarlton said:

Any idea if there are any other bronze wear items other than the small end rod bushings? 

Yes, SB480F lists as possible sources of bronze the following: 

Connecting rod bushings
Rocker bushings
Crankshaft bearings
Intake valve guide
Piston pin plug
Idler gear bushing

[EricJ]

12 minutes ago, AndreiC said:

My reading of the SB480F is that chunks are 3/16" or greater, indeed, but chips are greater than 1/16". Their distinction seems to be into the three categories "chunks", "chips" and "small metallic particles".  For example they say "Use non-metallic tweezers or a pick to sort chunks, chips, and particles that look different." Or they say "Yet metallic particles can be small dust-size particulates - that is where quantity becomes more of the issue in this case." 

Also Table 3 states that "1 to 9 pieces of metal (1/16 in. (1.2 mm)) diameter or less)" is fine and you should continue to operate the engine to the next scheduled oil change. So I assume such pieces are not chips.

The 3/16" chunks will likely be in the suction screen, and the smaller stuff will likely be in the pressure filter.   I'd think it'd be pretty rare for a 3/16" chunk to show up, and I'd think it'd be rare for something big to show up without smaller stuff showing up, too, but they haven't really described the failure modes very well.

It'd show up in the spectrographic analysis as increased copper, which could also come from the other sources that you just listed.

[PT20J]

1 hour ago, AndreiC said:

My reading of the SB480F is that chunks are 3/16" or greater, indeed, but chips are greater than 1/16". Their distinction seems to be into the three categories "chunks", "chips" and "small metallic particles".  For example they say "Use non-metallic tweezers or a pick to sort chunks, chips, and particles that look different." Or they say "Yet metallic particles can be small dust-size particulates - that is where quantity becomes more of the issue in this case." 

Also Table 3 states that "1 to 9 pieces of metal (1/16 in. (1.2 mm)) diameter or less)" is fine and you should continue to operate the engine to the next scheduled oil change. So I assume such pieces are not chips.

The SB does not define the size of chips other than to say they are smaller than chunks. The first entry in Table 3 that you quote is for metal in general, but later in the table it specifically indicates that finding any bronze in the screen or specified number of chips in the filter leads to corrective action 6 or 7 which is removing cylinders.

[ArtVandelay]

Yes, SB480F lists as possible sources of bronze the following: 
Connecting rod bushings
Rocker bushings
Crankshaft bearings
Intake valve guide
Piston pin plug
Idler gear bushing

Intake valve guide but no exhaust valve guide?

[EricJ]

4 hours ago, ArtVandelay said:

Intake valve guide but no exhaust valve guide?

They're different materials.    The exhaust valve components get much hotter than the intake.

[DCarlton]

https://www.aopa.org/news-and-media/all-news/2024/november/07/new-ad-concerns-lycoming-connecting-rods?utm_source=epilot&utm_medium=email

[A64Pilot]

I can’t imagine a piece of bronze coming from the small end bushing being 3/16” without the bushing pretty much coming apart.

Pieces of metal even 1/16 would have me very concerned.

I’d expect the failure mode to begin with small flakes that progressively get bigger, but good Lord 3/16” “chunks”? 

Am I the only one that never sees metal in their filters? I need to quantify that as I sometimes see a very small amount iron so small it feels like grease on the magnet

[DCarlton]

2 hours ago, A64Pilot said:

I can’t imagine a piece of bronze coming from the small end bushing being 3/16” without the bushing pretty much coming apart.

Pieces of metal even 1/16 would have me very concerned.

I’d expect the failure mode to begin with small flakes that progressively get bigger, but good Lord 3/16” “chunks”? 

Am I the only one that never sees metal in their filters? I need to quantify that as I sometimes see a very small amount iron so small it feels like grease on the magnet

Yep.  Again, I'm no expert, but if I see bronze / copper / tin show up in an oil analysis, I'll probably watch it closely over time.  If I see any bronze particles, chips, or chunks of any significance, I'll probably inspect / press test / and if necessary replace the bushings.  But again, I'm no expert and I'll listen to the experts.