Silk thread vs sealant

The 0200 on my wife's plane has oil seeping around one of the through cylinder studs that pulls the case halves together. It'll interesting some day when rebuild time comes to see whether they used thread or hylomar.
 
Excellent article.

The Skyranch Engineering book goes into great detail on this subject as well. The book is an excellent resource. I also liked his website and have the computer guide which is all worth the money on my opinion.

I was taught to follow the manufacture guidance, especially in critical areas such as installing cylinders, assembling crankcase, spar repairs, flight controls, etc. When you start changing the basics, you change the basic design and that may not be good, just as happened in the accident linked to above.

Good report for case study. :)
 
JAWS said:
Excellent article.

The Skyranch Engineering book goes into great detail on this subject as well. The book is an excellent resource. I also liked his website and have the computer guide which is all worth the money on my opinion.

I was taught to follow the manufacture guidance, especially in critical areas such as installing cylinders, assembling crankcase, spar repairs, flight controls, etc. When you start changing the basics, you change the basic design and that may not be good, just as happened in the accident linked to above.

Good report for case study. :)
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The accident mentioned in the article is related to using thread and goo around the bearing bosses, not the case parameter.
 
The entire paragraph from the NTSB report linked above.

"The crankcase was intact and undamaged. The crankcase halves were split, and the crankcase was visually inspected. It was noted that there was black sealant applied to the crankcase halves mating surfaces, and there was no silk thread noted on the crankcase halve mating surfaces. It was also noted that the black sealant material was found in several of the oil galleys. There were no signs of bearing shift or lock tab elongation. The accessory case displayed damage on the inside of the case; the damage was consistent with impact with the sheered crankshaft gear bolts. All three main bearings remained within their respective bearing supports. Each displayed normal operating and lubrication signatures.".

Tom-D said:
The accident mentioned in the article is related to using thread and goo around the bearing bosses, not the case parameter.
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Not sure where these specifics come from, or what is meant by 'parameter' is in this instance, but maybe the poster will chime back in and explain clearly.
 
I used loctite 515 on my o-360 and it’s doing great so far. 70 hours on it already.
 
JAWS said:
Not sure where these specifics come from, or what is meant by 'parameter' is in this instance, but maybe the poster will chime back in and explain clearly.
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He means perimeter. The case flanges around the outside, where oil leakage is the big problem.

The article is warning about thread around the through-studs where they pass through the bearing saddles. Thread will keep those faces apart and let relative movement occur, and as the thread disintegrates the tension on the bolt decreases somewhat. Mechanics might put thread and sealant there to try to prevent oil leaking out along the through-bolt and appearing at a cylinder flange nut. It's a problem.
 
This Service Letter issued by Continental specifies what to use on their engines. https://www.google.com/url?sa=t&rct...sil99-2b.pdf&usg=AOvVaw1nAOkyV5gZQ1yo-yaGl2D8

For crankcase parting faces and a few other spots they want Permatex Aviation 3D sealant, which we know as Aviation Form-A-Gasket, and silk thread.

Read it closely and see that nowhere do they suggest RTV as being OK. I wish mechanics would keep RTV away from anything involving fuel and oil. Ditto with teflon tape.
 
Dan Thomas said:
This Service Letter issued by Continental specifies what to use on their engines. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwiz4dLYj8HgAhVJ34MKHcsDAZsQFjAAegQICRAC&url=http://www.hangar9aeroworks.com/aeroncatechinfo/sil99-2b.pdf&usg=AOvVaw1nAOkyV5gZQ1yo-yaGl2D8

For crankcase parting faces and a few other spots they want Permatex Aviation 3D sealant, which we know as Aviation Form-A-Gasket, and silk thread.

Read it closely and see that nowhere do they suggest RTV as being OK. I wish mechanics would keep RTV away from anything involving fuel and oil. Ditto with teflon tape.
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Question for ya DAN,,
For decades mechanics have been using silk thread, Why?
why not a cotton thread? linen thread?

Second question, when you send your cases in and have the CRS Lapp and line bore them so that every clearance is perfect, why would you put a substance in between them that will hold them apart?
 
Tom-D said:
Question for ya DAN,,
For decades mechanics have been using silk thread, Why?
why not a cotton thread? linen thread?

Second question, when you send your cases in and have the CRS Lapp and line bore them so that every clearance is perfect, why would you put a substance in between them that will hold them apart?
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Whats wrong with just following the manufactures guidance?
 
Tarheelpilot said:
Whats wrong with just following the manufactures guidance?
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The cost of up dating the guidance has the manufacture 25-50 years behind the current technology. last update of the 0-200 manuals was 2011, and TCM kept the thread because they know there will be field overhauls that will not have the cases lapped and line bored.

Plus, we all know that the A&Ps of the past never sent the cases in to be reworked, thus they needed the thread to fill gaps in the old cases. but today we all send the cases to be re-worked, So we really don't need the thread. we need to know the bearing clearances and the thru bolts going thru the bearing bosses will stay torqued.

Read the Forward in the 0-200 overhaul manual, and tell me where it says this manual is mandatory in nature.
 
Tom-D said:
TCM kept the thread because they know there will be field overhauls that will not have the cases lapped and line bored.
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Apparently Tom now speaks for TCM. Good to know!

Tom-D said:
Plus, we all know that the A&Ps of the past never sent the cases in to be reworked, thus they needed the thread to fill gaps in the old cases. but today we all send the cases to be re-worked, So we really don't need the thread.
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I bet this is the reason for this. He wants someone to agree with him that the thread isn't needed.

Tom-D said:
Read the Forward in the 0-200 overhaul manual, and tell me where it says this manual is mandatory in nature.
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Does TCM or the FAA make the rules of what is or isn't mandatory? I think your answer lies in the regs. Something about using the most current manufacturer's maintenance manual.
 
Tom-D said:
The cost of up dating the guidance has the manufacture 25-50 years behind the current technology. last update of the 0-200 manuals was 2011, and TCM kept the thread because they know there will be field overhauls that will not have the cases lapped and line bored.

Plus, we all know that the A&Ps of the past never sent the cases in to be reworked, thus they needed the thread to fill gaps in the old cases. but today we all send the cases to be re-worked, So we really don't need the thread. we need to know the bearing clearances and the thru bolts going thru the bearing bosses will stay torqued.

Read the Forward in the 0-200 overhaul manual, and tell me where it says this manual is mandatory in nature.
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I never said, thought nor implied it was mandatory therefore your challenge for me to prove it is mandatory is rather odd.

I asked a simple question. Why not follow the manufacturer recommended procedures. You answered that question. No need for the argumentative rhetoric
 
JAWS said:
Apparently Tom now speaks for TCM. Good to know!
I believe you draw the wrong conclusion, I speak for me, and what I believe to be true.
I bet this is the reason for this. He wants someone to agree with him that the thread isn't needed.
No-one needs to agree with me, few will learn, others won't. The carry on engine 0/IO 240 doesn't require it, why?
Does TCM or the FAA make the rules of what is or isn't mandatory? I think your answer lies in the regs. Something about using the most current manufacturer's maintenance manual.
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The FAR that does that is FAR 43.2. and there is no mention of any maintenance manual. even the overhaul manual says that it is guidance, not regulatory in nature.

Don't forget, A&Ps are authorized to make minor alterations to engines and A/Fs
 
Tom-D said:
Question for ya DAN,,
For decades mechanics have been using silk thread, Why?
why not a cotton thread? linen thread?

Second question, when you send your cases in and have the CRS Lapp and line bore them so that every clearance is perfect, why would you put a substance in between them that will hold them apart?
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First, silk is very fine, has higher tensile strength than cotton or linen. Second, which is probably the real reason, is that it's expensive, so it fits into the aviation business nicely.

You shouldn't need thread around the thru-bolts at the saddles. If that area is nicely lapped and everything is torqued properly, there should be very little leakage into the stud bore. The perimeter is different: it isn't so solid and stiff as the bearing saddles, and simply tightening the small bolts will cause a small amount of waviness that results in leakage. So the manufacturers recommend the thread and sealant.

Now, on this debate as to whether the overhaul manual is mandatory: What does FAR 43 say?

§43.13 Performance rules (general).
(a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator, except as noted in §43.16. He shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices. If special equipment or test apparatus is recommended by the manufacturer involved, he must use that equipment or apparatus or its equivalent acceptable to the Administrator.

So it's either the "current manufacturer's maintenance manual," or "other methods, techniques, and practices acceptable to the Administrator..."

My opinions or personal shop habits won't be acceptable to the administrator. I would need to come up with my own manual and have it approved. Only a big outfit could afford that sort of thing.
 
Dan Thomas said:
First, silk is very fine, has higher tensile strength than cotton or linen. Second, which is probably the real reason, is that it's expensive, so it fits into the aviation business nicely.

You shouldn't need thread around the thru-bolts at the saddles. If that area is nicely lapped and everything is torqued properly, there should be very little leakage into the stud bore. The perimeter is different: it isn't so solid and stiff as the bearing saddles, and simply tightening the small bolts will cause a small amount of waviness that results in leakage. So the manufacturers recommend the thread and sealant.

Now, on this debate as to whether the overhaul manual is mandatory: What does FAR 43 say?

§43.13 Performance rules (general).
(a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator, except as noted in §43.16. He shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices. If special equipment or test apparatus is recommended by the manufacturer involved, he must use that equipment or apparatus or its equivalent acceptable to the Administrator.

So it's either the "current manufacturer's maintenance manual," or "other methods, techniques, and practices acceptable to the Administrator..."

My opinions or personal shop habits won't be acceptable to the administrator. I would need to come up with my own manual and have it approved. Only a big outfit could afford that sort of thing.
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That is a big "OR" and what you were taught in A&P school is acceptable to the Administrator.
 
Dan Thomas said:
First, silk is very fine, has higher tensile strength than cotton or linen.
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Why would it need strength when trapped between to surfaces?
Silk is hard. it will in fact indent into aluminum surfaces, thus seal better than any other material. It has been use from a time when we had no real sealants as we do today.
 
Dan Thomas said:
My opinions or personal shop habits won't be acceptable to the administrator.
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Unless you are doing major repairs, it will be acceptable to the administrator, Here is the simple question that proves that. is a complete overhaul of an engine a major repair? If it is, why can A&Ps do them.
 
Tom-D said:
That is a big "OR" and what you were taught in A&P school is acceptable to the Administrator.
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Fine with me. I'm a Canuck and answer to some different folks who take a different view of such things. They can be quite fussy.
 
Dan Thomas said:
My opinions or personal shop habits won't be acceptable to the administrator. I would need to come up with my own manual and have it approved.
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As a thread drift and FYI: your opinions and personal shop habits could very well be acceptable to the Administrator. And they do not require your own "approved" manual. Hence the term "acceptable". By regulation the Feds have the burden to show your opinions/habits are not correct or acceptable. That is one of the benefits of the FAR system. And it's sometimes a detractor as it provides environment where more than one method is correct. Having worked within various CAA systems over the years it has always been my experience that a good number of mechanics outside the States prefer the FAR system due to its flexibility in maintaining aircraft. Good, bad, or indifferent I too prefer its flexibility to get the job done properly.
 
Bell206 said:
As a thread drift and FYI: your opinions and personal shop habits could very well be acceptable to the Administrator. And they do not require your own "approved" manual. Hence the term "acceptable". By regulation the Feds have the burden to show your opinions/habits are not correct or acceptable. That is one of the benefits of the FAR system. And it's sometimes a detractor as it provides environment where more than one method is correct. Having worked within various CAA systems over the years it has always been my experience that a good number of mechanics outside the States prefer the FAR system due to its flexibility in maintaining aircraft. Good, bad, or indifferent I too prefer its flexibility to get the job done properly.
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Sorry, but I am not convinced. I understand that it is the FAA's burden to prove that your personal habits are not acceptable, but that is pretty broad. When I went through tech school, it was my understanding that I was learning the acceptable way to do things, and these various teachings were evaluated by the regulator as meeting industry standards. And the industry is supposed to use "acceptable" data for the most part. An engine overhaul deserves better than "I know best"!

I wonder what owners would really think if they knew ahead of time that Mr Mechanic was going to use processes and materials different from the overhaul manual because he thinks it is better? Would the owners think it is such a great thing if they knew the different what ever may become an issue at a later date, like after their aircraft crashes and the FAA gets involved and those involved have to start defending themselves? I wonder what the insurance companies and the lawyers would think if asked ahead of time?

Way too much liability for my tastes. I will gladly follow set practices and products and will leave others to dabble in the grey area.
 
The engine internals were modified (balanced) using an ad hoc procedure. No approved or even acceptable data available.
 
JAWS said:
The engine internals were modified (balanced) using an ad hoc procedure. No approved or even acceptable data available.
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major repair with unapproved method.
Plus he didn't test in accordance with any approved method.

the more I read about this case the more I believe he got off with a slap on the hand.

Getting back to the sealant issue, leaving it out, or using a silk thread is not a major alteration.
 
Tom-D said:
major repair with unapproved method.
Plus he didn't test in accordance with any approved method.

the more I read about this case the more I believe he got off with a slap on the hand.

Getting back to the sealant issue, leaving it out, or using a silk thread is not a major alteration.
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:eek:
 
JAWS said:
And the industry is supposed to use "acceptable" data for the most part.
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Define acceptable? We’re not talking about a free-for-all here, rather a certified mechanic making a determination to perform maintenance in an acceptable manner. The FARs are written to support this method. Hence the reason the Feds must prove it wrong.

Just look at Part 43.13:
shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator,

The key word is “or.” The mechanic determines which “acceptable” method to use not the FAA. Per 43.13 a mechanic can even use a different method when one exists in the OEM MM or OH manuals--which by the way is only “acceptable data” and not “approved data.” Does the FAA encourage the use of OEM methods, yes, but they don't mandate their use either except in accordance with 43.16. This point is supported by several FAA legal and regulatory guidance documents.

Actually, this is no different than a mechanic or pilot determining the airworthiness of an aircraft. Each person’s definition will be different--as we’ve seen on POA--but in the eyes of the FAA each definition is acceptable until proven otherwise.

And while you may prefer to “follow set practices and products” that is you’re prerogative as a certified A&P. But what if there are no set practices or products for the aircraft or task you need to work on? Most aircraft don't have a procedure for every possible maintenance task nor does every aircraft have a MM. Is there a "set" aircraft alternator procedure that checks for the amount of factory applied internal bearing grease or internal diode check as a means to troubleshoot a faulty aircraft alternator? If not does that make the procedure "unacceptable?" Or simply a smart acceptable way to fix/determine a problem. Most mechanics have their own LBB methods that work and in some cases provide an acceptable solution where no solution exists.

JAWS said:
I wonder what owners would really think if they knew ahead of time that Mr Mechanic was going to use processes and materials different from the overhaul manual because he thinks it is better?
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And as a mechanic I wonder ahead of time how much maintenance the owner performed without the use of proper processes, materials, or logbook entries because they think they know better or are too cheap to bring it to a mechanic. I think you'll find this issue of a mechanics use of acceptable data is rather small in the big picture especially Part 91 ops.
 
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Bell206 said:
Define acceptable? We’re not talking about a free-for-all here, rather a certified mechanic making a determination to perform maintenance in an acceptable manner. The FARs are written to support this method. Hence the reason the Feds must prove it wrong.

Just look at Part 43.13:
shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator,

The key word is “or.” The mechanic determines which “acceptable” method to use not the FAA. Per 43.13 a mechanic can even use a different method when one exists in the OEM MM or OH manuals--which by the way is only “acceptable data” and not “approved data.” Does the FAA encourage the use of OEM methods, yes, but they don't mandate their use either except in accordance with 43.16. This point is supported by several FAA legal and regulatory guidance documents.

Actually, this is no different than a mechanic or pilot determining the airworthiness of an aircraft. Each person’s definition will be different--as we’ve seen on POA--but in the eyes of the FAA each definition is acceptable until proven otherwise.

And while you may prefer to “follow set practices and products” that is you’re prerogative as a certified A&P. But what if there are no set practices or products for the aircraft or task you need to work on? Most aircraft don't have a procedure for every possible maintenance task nor does every aircraft have a MM. Is there a "set" aircraft alternator procedure that checks for the amount of factory applied internal bearing grease or internal diode check as a means to troubleshoot a faulty aircraft alternator? If not does that make the procedure "unacceptable" or simply a smart way to fix/determine a problem. Most mechanics have their own LBB methods that work and in some cases provide a solution where no solution exists.


And as a mechanic I wonder ahead of time how much maintenance the owner performed without the use of proper processes, materials, or logbook entries because they think they know better or are too cheap to bring it to a mechanic. I think you'll find this issue of a mechanics use of acceptable data is rather small in the big picture especially Part 91 ops.
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You mention two terms that are misunderstood by many people.
"acceptable data", "acceptable methods".
Explain the difference.
 
Bell206 said:
Just look at Part 43.13:
shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator,

The key word is “or.” The mechanic determines which “acceptable” method to use not the FAA. Per 43.13 a mechanic can even use a different method when one exists in the OEM MM or OH manuals--which by the way is only “acceptable data” and not “approved data.” Does the FAA encourage the use of OEM methods, yes, but they don't mandate their use either except in accordance with 43.16. This point is supported by several FAA legal and regulatory guidance documents.
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I'd agree with this to a point, An A&P must full fill their duty to safety. Use of sealant rather than silk thread is one thing, and a decision the A&P is authorized to do. Sending parts to a uncertified repair station, and then not testing the equipment is totally beyond the realm of proper maintenance IAW FAR 43.13
And then signing the return to service entry as complying with FAR 43.2 when you didn't, will PO the FAA more than anything I know.
 
Cap'n Jack said:
One nice thing about the silk thread is that too much can't be applied- too much sealant can get into places it shouldn't
https://www.ntsb.gov/investigations...ev_id=20150928X72825&ntsbno=WPR15FA268&akey=1
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Man. If you ever make a professional mistake - it’s going to be fun to watch karma strike back. Universe is nice that way. Your obsession that causes you to continually post a reference to a NTSB report involving Tom in Tom’s threads tells everyone a lot about you.

The NTSB investigated. The FAA handled it. However that doesn’t mean Jack is done with it!

I know who I’d rather hang with. The guy who turns wrenches and tries to help. Versus the guy who picks on elder veterans and can’t ever let an issue drop.
 
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