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MG Midget and Sprite Technical - Petrol thread sealant

What sealant should I use on a petrol pipe fitting please?

(I didn't want to use PTFE tape in case any came off and blocked somewhere.)

Background;
I found I had a very small leak on my fuel tank outlet whilst doing other work in that area.

The tube nut had been rounded off by a previous person so I decided to order a new pipe and fittings (copper pipe with nipple pre-soldiered (at an angle!) and tube nut).

I fitted the new tube nut dry and now I still have a leak, possibly slightly more than before.

I don't want to replace the tank at the moment if I don't have to.
Nigel Atkins

Nigel
Try a dab of hylomar.
Alan
Alan Anstead

Hi Alan,
thanks for your reply, do you mean the blue general stuff?

And if so how long does it keep do you know, I ask as mine is from August 2014 and is kept in a shed that freezes and gets very warm, the red stuff I had separated out a bit in the heat of last summer so I replaced it just in case before using.
Nigel Atkins

Alternatively, a small dab of household gloss paint on the cone surface of the nipple and the thread, then do the fitting up whilst the paint is wet.
GuyW

Thanks Guy I'll bear that in mind as I was hoping to only remove the tube nut and not disturb the pipe again - surprising little room for my arms under there when I have to wear a thick jacket as it's so cold and it happens just after I've reconnected to handbrake rods - plus I'd need to go to my neighbour for gloss paint, but I will bear it in mind.
Nigel Atkins

I think you may have to take it apart for a good inspection as to why its not seating - dirt/grit/high spots/flux residue/solder or badly machined taper etc.

I Understand access restrictions but if you can push the cones together and rotate a few times it may bed together a bit better.

It should not need any sealant - I use similar fittings on high pressure steam!


richard b

My experience of the design is that it shouldn't require any sealant to be leak free as the tube nut pushes the male taper end of the fuel line against the female taper of the tank pick-up causing it to seal the two and against the tank boss. A leak would indicate further damage resulting in the leak. It's like a propane POL fitting in that the seal is made due to metal to metal contact and if a leak is present it indicates damage to the sealing surfaces which should be investigated. I have seen people use PTFE on propane and even oxygen connectors which can be dangerous as PTFE tape for oxygen must be O2 rated and not all is.
David Billington

David, I've never heard that about PTFE and oxygen before. I've used rolls and rolls of it on gaseous and liquid oxygen over the years as well! The stuff we used was officially supplied so may have been the right type but it's not something that was ever mentioned in any of the courses I've done or equipment manuals I've read. Have you got a reference so I can check we are using the right type at work?
John Payne

John,

A quick look for "ptfe oxygen rated" turns up these links and others.
http://www.the-gas-safety.co/PTFE-Tape---Oxygen-grade-to-EN751-GRp.aspx
http://www.cobasuk.com/
http://www.sealtape.com/ptfe_green.html
http://www.boconline.co.uk/en/products-and-supply/industrial-gases/oxidant-gases/oxygen/oxygen.html
http://m.restek.com/pdfs/308-02-001.pdf

I've bought and used PTFE tape in the past specifically marked as compatible with oxygen.
David Billington

Yeah, I should have done a more thorough job, waited for a better time and more inclination but I discover these things at less convenient times and I want/need to use the car.

I'll have to get my picks out, a magnifying glass and a good torch but I've no idea where I'll get a good set of eyes from.

It can wait until I use up the full tank of fuel and fulfill the commitments my wife has set up that "I should do" even though I don't want to and they're during the times I could be fixing the car in good weather instead of cold or wet.

I may try Guy's trick.
Nigel Atkins

Nigel,

Maybe a copper washer would help between the joint, I have some dished copper sealing washers for gas sealing like roves http://www.faeringdesigninc.com/fst-rve.html and am sure I got them from BES gas but can't find them so they either don't do them any longer or their improved? website isn't.
David Billington

Tasmanian emergency version
Remove the tube nut,
Work some soap up into a paste and apply a smear between the banjo and the tank, another smear on the surface of the banjo where the nut goes, refit the nut and tighten it up , loosen it quarter of a turn and finally tighten it-The petrol will react with the soap and seal it off
Works for me
willy
William Revit

Nigel, you said
'new pipe and fittings (copper pipe with nipple pre-soldered (at an angle!)'
the nipple has to be square on the pipe, so I deduce you have another faulty part. I don't see why you should have to bodge it (for any form of sealant here is bodging in my book). Raise a complaint, send it back, get a correctly made one.
David Smith

Nigel


I agree with the above - should fit metal to metal on the tube and the thread without any sealant tape.

Is this a cross threaded fitting, or perhaps poorly made profile of the thread/incorrect thread on the new fitting? Did the old fitting come off OK once loosened or had the thread been bodged/damaged previously?

Good luck and shame this is beyond the Driver's Handbook beyond 'always fit BL/BLMC genuine parts' that is probably in the front of said 'Good Book'.

Are you anywhere near Think Automotive in W London or Mallory Park race circuit (Merlin Motorsport), as they may be able to help you by making up replacement using the old one as a pattern? Just checked your location - Northampton, try Raceparts or Trident Racing Supplies for the end fitting.

Cheers
Mike
M Wood

Nigel

Is this the part in question: http://www.leacyclassics.com/aha7381.html

Cheers
Mike
M Wood

Cheers David, I'll check what we use at work in the new year. Let's hope I don't end up grounding the fleet!!
John Payne

Hi All, thanks for your replies.

I think the cock-eyed soldiering hopefully shouldn't matter (I hope) as the pipe is 6mm and tube nut internal about 9+mm so there's room for it to be off square and still snug down plus the pipe has to be bent near that point.

I left enough tail the other end so that if I needed I could cut off that nipple and soldier on a replacement.

The previous tube nut wasn't crossed threaded as far as I could feel. When and why it was rounded off I don't know as I've never looked at it before.

The Leacy part is what I first expected the fittings would be i.e. with olive but the previous and new parts are with a soldiered nipple.

I ordered the pipe, tube nut and nipple as three parts to discover that the pipe came with the nipple (cock-eyed) soldiered on and tube nut without saying so so I have spares.

It's a less expensive copy of this - https://www.moss-europe.co.uk/pipe-fuel-tank-to-pump-flexible-aha7381z.html?assoc=419947

Looking at the original nipple under a magnifying glass I see a fairly irregular indent, I don't know if this is where the nipple mates up to the tank fitting or perhaps a suggestion of the potential problem.

I'll clean out the fitting on the tank this time, something I was reluctant to do last time in case chemicals didn't mix (not sure why as petrol would probably win) or leaving cleaning materials in the fittings. This time I'll try using an electrical contact cleaner, as it evaporates and a small pipe/bottle cleaner brush. I'll also use the cut off tail and nipple of the previous pipe to run round the face of the tank fitting to see if I can feel anything, difficult to do with the new pipe now it's bent.

Soap - always a lot of soap and washing up liquid used every time I touch anything on the car.

Hopefully I won't need to search for a dished washer.

I'll report back and not completely fill the tank until I know it's sorted, cheers.
Nigel Atkins

I bought a Moss one of these tank fitting pipes to go on a new (Canadian manufacture) tank for the Frog. When I assembled it I found that the thread length on the tube nut wasnt long enough and the flats of the nut bottomed out on the female threaded fitting on the tank before the nipple was clamped up tight.

I solved it with the addition of a couple of copper washers between the nipple fitting and the tube nut, but I had to do some filing as all the washers with a large enough hole to go over the stem part of the nipple, were too large externally to fit within the tank ferule.

Incidentally - the gloss paint tip was an emergency fix rather than the "right way" of assembling these. It was on the assumption that most people would have the odd tin of gloss paint lurking somewhere under the stairs. The exact shade doesn't matter.
GuyW

There are plenty of spare threads on the fitting on mine.

For me not only no paint of any shade but no stairs, sometimes there's just no helping some people. :)
Nigel Atkins

Are you sure you have no stairs Nigel? Have you checked recently? I would complain to the builders as it does seem to be a very basic omission.
GuyW

It was only when I got halfway on the stairs and couldn't remember if I was going up or down that I remembered we didn't have stairs.

Now what did I come in this room for . . .
Nigel Atkins

Nigel,

From the link you posted of a similar pipe fitting I think the issue (apart from the 'cock-eyed soldiering') could be that the threads in the tank are not tapped deep enough or / also the new threaded fitting does not have a 'waist' machined into the very end to allow it to pull up tight where the threads are not tapped deep enough - ISTR the originals had the 'waist'.

We recently had the same with a mates TR2 tank and sorted that one by running a 'plug' tap (square ended) 1/4BSP into the tank and deepening the thread by about a turn.

Not sure what thread the midget tank ? (anybody ?) is but I could lend you a tap if its the correct size - just post it back to me.

Another simple fix is to carefully file away just the thread portion of the first couple of threads from the brass nut going into the tank (small needle files etc are O.K for this) to create the waste - this allows the threaded portion to go in a bit deeper and put the required pressure onto the nipple tapers and form a seal,

To determine what the problem is I would slacken the nut and slowly tighten it - checking to see when the pipe goes tight when turning the pipe by hand (if at all !) - it needs to go tight and then have a couple of flats to finally 'nip it up' to seal.

If the nipple is really misaligned send it back as this can cause it to bind within the hollow bolt.

R.
richard b

Hi Richard,
thanks for your advice I will follow it up. The leak was also with the previous pipe, fitting and tank that were installed before I got the car 10 years ago so I'm not sure why it only started leaking recently.

I also don't know why and when the tube nut got rounded, it might have been like it since I got the car as I've never looked or taken any notice as there's never been a problem there.

Thank you very much for your offer and if I need to I will take up your offer, I don't know what the thread is but I'm not sure it's BSP as it didn't thread into a gas cap fitting I have but I didn't try too hard in case threads were lost so could be wrong.
Nigel Atkins

As soon as I left the computer I thought that doesn't sound right so I found another cap and can confirm -
the thread is 1/4" BSP -
sorry.

Sod's Law the unmarked cap I picked up was a very tight thread when I checked it with three plugs I found so I tried the tube nut in another (marked) cap that had better cut threads. As I've had these parts for decades and can't remember where I got them it shows poor quality fittings go back decades.

As I have a spare tube nut I can risk trying try filing off the first couple of threads if required, I don't have any needle files but I've got some small files.
Nigel Atkins

This thread was discussed between 22/12/2017 and 24/12/2017

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