PTFE or not PTFE that is the question

[cymaz]

I’ve got several SC 46 2t engines. All have, to some degree, loose HS needle threads. I assume from poor tolerances on manufacturing and age.

I've added an extra O ring of fuel tube on the needle shaft. 

 

What good would adding PTFE tape around the threads do? Does the tape deteriorate in the presence of glow fuel?

 

Thanks!

 

[Paul De Tourtoulon]

I don't know how what your needle valve looks like, but we used to put a bit of silicone fuel tubing on it as a sleeve, it stopped air leaks and unscrewing due to vibration.

[Nigel R]

Used to? Still do on some of my needles...

[J D 8]

 As above, a simple fix that works.

[Ace]

Not actually tried it on needles as fuel tube has been sufficient however - I do use a length between the cylinder and exhaust on up to .53 2* (just wide enough). This seals brilliantly and doesn't slacken off due to compression being so thin and also appears to be fuel tolerant. I believe it comes in two thickness 1) thinner for water 2) thicker for gas. I use the thicker one on exhausts but probably a bit thick for the fine needle thread - try the thinner one. Remember to wrap it so it tightens when screwed in 😉

Could also work on loose 4* exhaust?

Edited April 9 by Ace

[Manish Chandrayan]

8 minutes ago, Ace said:

Not actually tried it on needles as fuel tube has been sufficient however - I do use a length between the cylinder and exhaust on up to .53 2* (just wide enough). This seals brilliantly and doesn't slacken off due to compression being so thin and also appears to be fuel tolerant. I believe it comes in two thickness 1) thinner for water 2) thicker for gas. I use the thicker one on exhausts but probably a bit thick for the fine needle thread - try the thinner one. Remember to wrap it so it tightens when screwed in 😉

Could also work on loose 4* exhaust?

I use the Teflon tape as a standard practice on all my four stroke exhausts, seals up the threads nicely.

 

Regarding the question from Cymaz, while the tape is glow fuel tolerant , and will also seal the needle threads, I would be more worried about the teflon tape pieces making way to the fuel passages in the NV assembly, this can happen as needles may need opening and closing/reinsertion and that can cause the tape to shed some pieces.

The O ring on the needle is what  seals and keeps the needle snug in the housing. If you have play change the O ring.

The fuel tube trick you have already employed should be also working fine   

[cymaz]

Fuel tube it is then. Thanks for all the views/ideas

[Cuban8]

3 hours ago, Paul De Tourtoulon said:

I don't know how what your needle valve looks like, but we used to put a bit of silicone fuel tubing on it as a sleeve, it stopped air leaks and unscrewing due to vibration.

Should never have stopped using Castor based fuels - used to bung up worn needle valve threads a treat.......😁

[GrumpyGnome]

Dumb question time.... where do you put the tube? (I think I know the answer.....)

[J D 8]

 There will be a gap between needle body and body of carb, threaded bit visible on most carbs. Piece of tube a tad longer, so both ends are squeezed in in normal run position.  Hwyl.