Fuel Injectors and Anti-Seize

Tim K · 09-08-2009, 07:18 AM

I need to prevent the threads from galling/cold welding between an aluminum 'fuel rail' and a brass fitting with NPT threads. However I'm paranoid about the possibility of getting some of this junk into the (electronic) fuel injector. What can I use? I purchased Loctite C5-A (Copper based) as it is appropriate for use with aluminum and brass.

I found a service bulletin on the web for an air cooled air plain engine where it describes the application of anti-seize to a fuel fitting up stream of a fuel injector. Basically it describes the sparing application a few threads up from the end of the male fitting.

The first time I didn't use anything and sure enough the threads got a little galled up when I took it apart. Now there's the issue of what the metallic bits from the threads would do to the injector...

Can anyone speak to this? I know enough not to use Teflon tape, but that's where my knowledge ends.

Any help here would be appreciated.

Tim K

legion · 09-08-2009, 07:36 AM

What about teflon tape? If you do it right, there shouldn't be anything dissolvable to end up downstream.

Can you loctite the parts and let them dry before installing?

Tim K · 09-08-2009, 08:28 AM

Chris,

It seems that stray Teflon bits are inevitable when you R&R a joint with this stuff. I suppose the anti-seize has a better chance of staying put.

Some Permatex and Loctite products are supposed to lock, seal, and prevent galling in petroleum applications. But there is no mention of their use with fuel injectors.

Maybe I'm just being paranoid but I don't know how I would troubleshoot a problem with a plugged/damaged fuel injector if it became a problem down the road.

It appears as though there is a 'yellow Teflon tape' available for use with petrol, but there is still the issue of stray PTFE bits.

legion · 09-08-2009, 08:51 AM

If you don't start the teflon tape until the 2nd or 3rd thread down, would that help minimize tape flakes?

Heel n Toe · 09-08-2009, 08:58 AM

Have you contacted Wayne about this? I'm sure he's dealt with the question many times.

island911 · 09-08-2009, 09:09 AM

galling won't be your problem, but the dissimilar metals will be. Chris has the right idea, IMO. Teflon (PTFE) properly applied, will be a lower risk solution than waiting for tin precipitates out of the brass to oxides. ...or is it the aluminum oxides that will go crazy? Well, anyway, you want to insulate the dissimilar metals; else deal with whichever metal-fur will grow best.

..And the fact that you have NPT threads helps make the teflon tape more stable --tapered threads, rather than a hard stop flange.

Tim K · 09-08-2009, 09:48 AM

Chris, island,

I think that would work fine for the initial installation. It's the subsequent installations I'm concerned about (i.e. pushing the stray bits in).

John,

I'll bet Wayne knows exactly what to do in this situation. I just he's got enough going on.

Chris,

re: the dissimilar metals, Brass is higher up the Galvanic Scale/Series (more noble) and therefore the aluminum will experience the corrosion. Interestingly, Copper (in the anti-seize) falls between then on the scale. I don't know what that means practically speaking. Maybe if you can limit the potential between any two adjacent materials you're better off overall?

I think maybe I should rethink what I'm doing and use an o-ring. Sigh.

Thanks everyone for your input.

Feel free to add to the discussion.

An image of what I'm working with:

Tim K

island911 · 09-08-2009, 10:12 AM

Ah. Pictures are good.

If you have a relatively small amount of brass to a large chunk of aluminum the process (galvanic corrosion) should be very slow in the Al.

911pcars · 09-08-2009, 12:19 PM

Permatex makes a product called PST; it's a teflon-based product in a paste form. Recommended by Carroll Smith for sealing threaded joints.

Sherwood

slakjaw · 09-08-2009, 12:30 PM

Yep thats what I would suggest as well the paste Teflon stuff.

Tim K · 09-08-2009, 12:36 PM

Hi Sherwood, Kyle

In the Permatex Catalog (page 30: http://www.permatex.com/documents/PermatexCanadaCatalogue.pdf) it sounds like a good product for the application, but like all of the other products I've been able to find, it does not specifically mention use with fuel injectors. Maybe I'm reading too much into this. Maybe they're all just fine. With all of the products stating use with 'fuel fittings' and being in this day and age, I can imagine that most vehicles would be using fuel injected engines. Not knowing what sorts of contaminants a fuel injector could shrug off makes me a little wary.

Thanks for the input.

Tim K

sammyg2 · 09-08-2009, 12:44 PM

Teflon tape is evil. Only use it on plumbing. No mechanical uses, ever. If you absolutely need to seal a low temperature application, use Teflon-based pipe dope (paste).
DuPont doesn't allow Teflon tape's use on the machines that make it.

paint the threads of your injectors with milk of magnesia.
No galling, no contamination, no problems. Same on your exhaust studs.
Use it on anything that can get over 400 degrees.

TimT · 09-08-2009, 04:18 PM

The injector has a little mesh screen as a final filter to catch things that get past the primary fuel filter. The injector could eventually become blocked if enough particles get past the primamry filter..

I've heard of the milk of magnesia trick but never used it... a little teflon pipe dope would work...

pic of an injector rebuild kit, the screen is top most in the pic

Tim K · 09-09-2009, 12:04 PM

Thanks all.

If many are using a teflon paste/pipe dope with good results, I will go that route. In the near future though I think I'm going to integrate a fitting with an o-ring. It would make it easier to service and avoid some potential problems.

FYI: Milk of Magnesia is the mineral Magnesium Hydroxide suspended in water (i.e. will dissociate into bits again when water evaporates)

Tim K