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Silk Thread??

A

avq

Member
I was having a hard time finding silk thread from my regular aviation parts suppliers so I decided to look for the thread at sewing suppliers. Still ?00? was hard to find. Frankly I did not really know what it meant so I decided to dig into it. Some of you folks in this forum may already know this so please correct me if I am wrong.

?00? is a Silk Machine Twist size. It basically implies that there is about 1100-1200 yards of thread per ounce. This actually varies by supplier making the matter more complicated. The military once specified their own sizing similar to Silk Machine Twist but more controlled.

The textile industry has standardized on the TEX which is 1 TEX = 1 gram per thousand meters of thread.

If you run the conversion for ?00? to TEX your get that ?00? is between 26-28 TEX. YLI #50 thread seems to fit the bill perfectly since it is TEX 27.

Now if Lycoming was referencing the military spec than all this goes out the window. ?00? from the military is closer to T-16. I doubt this was the case so I will personally go with the #50 thread from YLI.

Some of you are probably thinking, ?who cares?? or ?you need a life? And I would have to agree. I just had some time to kill this evening :)
 
Forget using silk on the case halves. Personally I use Proseal on the parting surfaces which works great...no leaks. That is the recommended sealant for sealing heads and banks we've used on a Merlin. I've had engines leak following the other officially recommended ways to seal cases.
 
Proseal?..Wow

Well I guess you don't exactly expect to take this apart very often..:)

Filed in the "If I ever have to do this" file.

Thanks

Frank
 
I had the same problem

avq said:
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Some of you are probably thinking, ?who cares?? or ?you need a life? And I would have to agree. I just had some time to kill this evening :)
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Not at all...

I had the same problem sorting it all out. So I ordered "00" silk thread from two different places. One was like rope compared to the other! I used the thinner of the two types. No leaks so far, two years and 450 hours.
 
Thread

The purpose of the thread is to keep the sealant from being completely squeezed out from between the case halves. It's really hard to find the approved sealant, so I just use Titeseal with the thread, and it works great.
 
When I cracked open my Mattituck TMX540 engine, I noticed that there were TWO silk threads sealing the case halves. So when I reassembled the engine, I put two silk threads back in there and used Pliobond as recommended by Lycoming. So far so good. Bought the 00 silk on eBay. Have about a gazillion feet of it left over if anyone needs some...

I like Bob's "proseal" idea, too!
 
az_gila said:
Isn't it a problem if the squeeze out is on the inside and blobs of ProSeal get into the oil?
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No. You apply it with your finger and thin out on the inner edges by wiping your finger across the edge before assembly. Once it sets up a bit you have a nice little bead on the outside that's easy to smooth out, which enhances the seal.
 
Hylomar?

My Super Late Model race car had a quick change rear end. Because the cover over the quick change gears had to be removed frequently, we used Hylomar as the gasket sealant. It worked well and didn't set up, so we never had to beat the cover off.

I heard an unsubstantiated rumor when I started using Hylomar (30 years ago) that is was the (then current) mating surface sealant of choice for Rolls-Royce. I always wondered if it would work on the case halves of a Lycoming.

The way the cylinders are attached on Lycomings, it doesn't surprise me that there can be movement and fretting (and leaking) at the crankcase parting line. Many higher time engines seem to wind up with epoxy along the parting line.

LarryT
 
Built my engine at America's Aircraft Engines in Tulsa and we used their standard procedure; Hylomar and 2 runs of silk thread. With over 1100 hours on the engine I have ZERO leaks.

We used to use Hylomar on the hot section oil covers on JT8's and many other places that called out for sealant, worked good on them so I figured it should be ok on my baby motor :D
 
49clipper

I always used Hylomar for my five engine rebuilds with no leaks. One silk thread also, but i like the idea of two.

Jim
RV-6
 
rocketbob said:
Just curious if anyone has ever seen silk thread after cracking a case open....I sure haven't.
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Almost every engine I have torn down ( Lycoming and Continental) has the thread between the case's. When I reseal I use aviation permatex (can be found at checker, Napa,Auto Zone, you get the idea. Along with 2 rows of silk thread. I have been building engines for over 20 years and knock on wood havent had any leaks. Usually when you are rebuilding an engine you are dealing with someone like aircraft specialties or the like to do your machining or purchase your parts. You will find that almost all of these places carry the 00 silk thread.
Ryan
 
Rivethead said:
I like not to touch any sealant with my fingers; it ruins my manicure and is more likely to be applied way too thick. A great way to apply sealant is to use a paint roller with a scant amount worked into the plush, enough to be sticky and then just paint it on being careful not to get it on internal channels and stuff. ......
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You can roll ProSeal?

I would have though that would just turn the roller into a sticky ball...:)
 
az_gila said:
You can roll ProSeal?

I would have though that would just turn the roller into a sticky ball...:)
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Yes and it's the preferred method for application when used as a fay surface seal. They even sell semkit guns with rollers built in or you can buy the rollers seperate. They kinda look like ink pad rollers with very little nap.
 
Just curious if anyone has ever seen silk thread after cracking a case open....I sure haven't.
I have also. It's really flat, kinda just fibers in the sealant. I've also noticed that it can make an actual groove or print right in the aluminum surface. I haven't checked the latest/greatest, but a few years ago the Lyc factory dropped the thread completely and used white RTV instead. Guess I should take a close look at my new factory engine and see what they're doing nowadays.
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Good Grief.

rocketbob said:
Forget using silk on the case halves. Personally I use Proseal on the parting surfaces which works great...no leaks. That is the recommended sealant for sealing heads and banks we've used on a Merlin. I've had engines leak following the other officially recommended ways to seal cases.
Click to expand...


See: Lycoming Service Instruction 1125D
 
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