Light Aircraft Association

Hello

I'm in the process of replacing the fuel system in a Kitfox. There are a number of 1/4" NPT brass fittings to reassemble. I know PTFE is a no, no, but I don't know which variant of Loctite is the accepted. Is Loctite 542 the one to use?

Fuel Lube is easiest - non setting.

Get in touch on PM with an address and I will send you a smear in a tiny poly bag

You don't need much and it is very, very sticky.......

Kevin,

I have the Loctite stuff (592) as I have recently done similar with my new fuel fittings.
I can send some if you like.
Tony

Fuel Lube despatched

Fuel Lube received thanks!

Will give it a go when my new tank finally arrives!

Loctite 592 in reserve if any problems!

Thanks chaps.

Why are you using a sealant ? If you are using perfectly good fittings, they don’t need sealant, especially the 592 stuff - getting the fittings apart again, if required, will be a problem. Introducing any form of contaminant to fuel lines - you know what happens !

I use 592 but ensure that the first three or four threads of the male fitting are left 'clean'. It's anti-galling properties allow you to get the fitting really snug.

592 does not set dead hard and there is absolutely no problem unscrewing the fittings - have done it many times.

Cleaning old sealant off the threads I have found to be a different matter! - especially the female ones.

Frank

Loctite 592 is a thread “locking” agent, not a sealant, and right there you have highlighted the problem with residue left on threads after they are undone - how can you be absolutely sure that you are making up the joint again without getting some of the stuff into the system. Galling ought not to be a problem (unless the fittings are in stainless steel). If there is concern about leakage, then either the joint is not assembled correctly or it the wrong choice of fitting in the first place.

Bill McCarthy wrote:Why are you using a sealant ? If you are using perfectly good fittings, they don’t need sealant

NPT fittings do need sealant, Bill. The threads are truncated, so there is leakage through the spiral form. That's why everyone else here is recommending a thread sealant.

Rob

Bill,

You are probably thinking of a different Loctite product:
Quote (from manufacturer's website):

"Thick acrylic dimethacrylate ester lubricating thread sealant paste which prevents galling on pipe threads and fittings.

LOCTITE® 592 is an opaque, off-white, thick acrylic dimethacrylate ester lubricating thread sealant paste which prevents galling on pipe threads and fittings. It provides immediate low pressure sealing and allows the readjustment of fittings shortly after assembly. The joint seals against pipe burst pressure after 72 hours. Suits applications up to +399 °F (+204 °C). Unsuitable for plastic piping.
Prevents galling on pipe threads and fittings
Provides immediate low pressure sealing and allows the readjustment of fittings shortly after assembly
High viscosity
Anaerobic cure"

I believe it is also recommended by Continental or Lycoming.
Tony