Silk thread for gaskets

[Fast Eddie]

I know the old boy hot rodders used to use silk thread to enhance gasket sealing properties.

Can anyone tell me exactly what kind of thread is best for this?

When I put ‘silk thread’ into an eBay search, it’s a bit mind boggling !!

 

[maaseyracer]

#50 A Grade is what we used to use, I still have ton of it that I will never use, but it is on the shelf just in case. From what I was taught it is best used on aluminum mating surfaces.

Edit: We used to bed it in Hondabond or a Toyota branded sealant of some sort it was black and I do not recall specifically what it was.

 

[texasSlick]

I am using #40. All other info on the spool is in Chinese. The thread diameter measures 0.005 inches.
I used the silk thread enhancement on my cylinder base gasket. Not a hint of a weep, but it was not a problem before.
I will give it a try on my timing cover gasket next time I have it off. Now, that, has always been a weeper!

 

[Fast Eddie]

Thanks for the input, I’ve sourced some now.

 

[Alan L]

Hi,
I’m rather sure that Rolls Royce Continental recommend silk as a seal between the cases of their aero engines, for whatever that’s worth
Alan

 

[Ctefeh]

CZ's too for crankcase halves

Sean

 

[Onder]

We used it on airplanes so it must work!
Truth is airplane work is seriously often old school.
Non-hardening Permatex and silk thread on crankcases
have also used it on solid copper head gaskets.

 

[Time Warp]

Kevlar thread.

 

[Fast Eddie]

We used it on airplanes so it must work!
Truth is airplane work is seriously often old school.
Non-hardening Permatex and silk thread on crankcases
have also used it on solid copper head gaskets.

Indeed, around the pushrod tunnels, with a copper gasket, is exactly what I want to use it for.

 

[YING]

Indeed, around the pushrod tunnels, with a copper gasket, is exactly what I want to use it for.

Nigel,
How is the silk thread applied?Do you set it in some type of sealant to hold it in place?
Thanks,
Mike

 

[Fast Eddie]

Nigel,
How is the silk thread applied?Do you set it in some type of sealant to hold it in place?
Thanks,
Mike

Yes.

But of course WHICH sealant would be another thread all by itself !

On the 920 I used the JS method of Pliobond and copper wire. It does seem to work, but the copper wire was horrible faff.

 

[Schwany]

Silk thread can't be that much fun to work with. Although it must be easier to lay down than copper wire in Pliobond. Just about anything would be easier to apply, and definitely easier to disassemble.

Purpose of the silk thread on aircraft is to prevent the sealant from being entirely squeezed out between mating surfaces when clamped together with fasteners. The silk thread doesn't compress to zero.

I turn the clock back 50 years and use aluminum brush on paint on all the head to barrel surfaces. The silk thread might work well in that scenario. Heck if I know though. Never heard of it until yesterday.

How much compression is the 1007 going to have?

 

[texasSlick]

I used the Pliobond/copper wire approach on my head gasket, on the underside only, as I was concerned the copper wire might dent the aluminum head. On upper side, I used copper gasket sealer only. I considered the silk thread on upper side but was unsure the thread could take the heat.

So far no oil weep which was present before, but Comnoz head skim may be the principal reason why.

Any one know if silk thread will hold up on upper side of head gasket?

Slick

 

[jseng1]

I used to go with the aero silk thread but switched to the fine copper wire. Its easier to install the hair fine wire if you stick it down on some pliobond glue - then add another coat of glue on top to keep it from moving. I have alum cylinders but don't really see any impression in the alum because the copper is softer. Still oil tight year after year.

 

[Fast Eddie]

How much compression is the 1007 going to have?

10.8:1… IF I’ve done my sums right …!

 

[Schwany]

10.8:1… IF I’ve done my sums right …!

That'll be healthy.

 

[Onder]

Silk thread will leave a tiny indent on copper. I anneal the cu first.

 

[MexicoMike]

You guys have lost me completely. I built competition engines for years and we always used gaskets made for the particular application. I do not understand what silk thread does that is better than a purpose-made gasket and I can't see any reason that silk thread (or copper wire) would function better as a gasket than a "real" gasket at any "normal" compression ratios - say 10.5:1 and below. For performance engines we generally used solid copper gaskets for the comp ratios at/below 10:5. Above that it was common to machine a groove in the block to accept a copper "O-ring." Later, when they became available, we used multi-layer steel head gaskets which can handle pretty much any compression ratio with no need for separate O-rings.

Of course, if the top of the cylinders/cylinder head(s) have warped or have otherwise faulty surfaces, this might require something special gasket-wise if it is decided not to correct the mating surfaces. But I cannot see why a Norton engine at ANY compression ratio I have ever heard mentioned, would need anything other than a readily available head gasket.

OTOH, I welcome any enlightenment since virtually all my experience in this area is with US V8 engines.

 

[Fast Eddie]

You guys have lost me completely. I built competition engines for years and we always used gaskets made for the particular application. I do not understand what silk thread does that is better than a purpose-made gasket and I can't see any reason that silk thread (or copper wire) would function better as a gasket than a "real" gasket at any "normal" compression ratios - say 10.5:1 and below. For performance engines we generally used solid copper gaskets for the comp ratios at/below 10:5. Above that it was common to machine a groove in the block to accept a copper "O-ring." Later, when they became available, we used multi-layer steel head gaskets which can handle pretty much any compression ratio with no need for separate O-rings.

Of course, if the top of the cylinders/cylinder head(s) have warped or have otherwise faulty surfaces, this might require something special gasket-wise if it is decided not to correct the mating surfaces. But I cannot see why a Norton engine at ANY compression ratio I have ever heard mentioned, would need anything other than a readily available head gasket.

OTOH, I welcome any enlightenment since virtually all my experience in this area is with US V8 engines.

The issue is not the head gasket joint sealing.

The common (ish) issue with Norton engines when using a solid copper gasket is oil weep from the pushrod tunnel area. This is more pronounced when using alloy barrels.

The idea is that putting thread or wire around those pushrod tunnels help the gasket acquire more clamping force at that specific point whilst not interfering in any way with the head gasket joint.

At least that’s the theory as I understand it.

 

[Alan L]

Hi all,
For over 40 years I have had the really basic 850 kit in my T160. That is modified 650pistons on standard bored our barrels. We all know that they are very prone to leaking because of the closeness of the bores. After initial sealing issues I had a small ring machined in the barrels to accept a ring of stainless wire. It has been successful and is till going strong.
Not that I’ve done huge miles on my bike but it is oil and gas tight.