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MG TD TF 1500 - Fuel filler neck pipe

I know this has been done to death in earlier threads, but most of the references are to using USA sink drain pipes manufactured in imperial measurements. And in the UK these are now in metric. So this is for UK owners.

I puzzled for quite some time about a solution and then realised that the rubber seal ring used in UK sink drain pipes just fits behind the sprung part of the filler cap and forms a very good seal for the tank while allowing venting. It does come adrift when you open the cap but it's easy to put back. I haven't had any fuel spillage since.

I 've put some pictures at

http://myweb.tiscali.co.uk/2mgtf1500/pages/petrol_tank_seal.html

Regards

David
David Wardell

David - Excellent solution! I think that it would even improve the old sink drain pipe solution. On item of caution, that 'O' ring s probably a nitrile (bauna N) rubber ring and as such will swell over time from exposure to petrol. The solution would be to get the diminsions of the ring (ID and cross section of the ring) and find some place that can supply the ring in Viton material, which is impervious to petrol. Cheers - Dave

PS if you can find those diminsions, I would sure appreciate knowing them, so I can give it a try.
David DuBois

Dave

The whole ring is 40mm in diameter. The cross section of the rubber is circular with a diameter of about 2.5mm.

I suspect you are right about the swelling - that's why you have to be careful to put the ring back in place every time the cap is opened.

The good thing about it is that it makes the cap a snug fit while maintaining the venting of the tank.

Regards

David
David Wardell

David W.,
Just a thought? Would a small dab of silicone sealant in two or three locations on the seal be enough to keep it from having to be put back into the proper location each time?
Gene
Gene Burgess

Gene - I can answer that for you - no it won't, the silicone will swell worse than the 'O' ring will and if it falls into the tank it can cause all sorts of trouble.

David - I take it that when you say the diameter of the whole ring is 40mm, you are refering to the outside diameter, is that a correct assumption? I will start looking for a source of viton 'O' rings that will fit and see if we can get a suply of them. Cheers - Dave
David DuBois

A WORD (actually, two) OF CAUTION:-

1. Gasoline will soften and can dissolve many rubber-based compounds. The O-ring you use shound be in Buna N (Nitrile) - a compund designed specially for gasoline and similar liquids. Also goes under different trade names including Perbunan, Hycar, Chemigum, and Paracril.

2. If you make this seal too tight, your engine may start, but not run for long. The reason is that the flow of fuel to the carbs depends on the entry of air through the fuel filler cap; and that's why on Triple M racers as an example, you'll see a small capilliary "pigtail" protruding from the filler cap or on the top of the tank. This way, a vacuum is prevented from building in the tank.

Not too long ago, I got a call from a friend who had just completed a multi-year restoration of his TD. The engine would start, but refused to run for more than a few seconds. One look at his gas cap solved the problem. He had installed an air-tight seal which prevented the flow of air through the tank.

Originally on the TF at least, the inside of the cap had a seal bonded to it, but mine wore out years ago and I don't plan to replace it; and I'll admit a little fuel will splash out on hard rh turns. So now, I don't fill my tank to the very top, for that reason.

With all due respect to Dave DuBois, Viton® while most useful with LMW esters (Low Molecular Weight esters like keytones, toluene, acetone, etc) may be overkill with gasoline, and typically has a higher durometer (is a harder compound) and is probably not as adaptable over a range of temperature and LMW effects). From my recollection, Viton does not take the "set" or "memory" of Buna N.

I have been out of the game for a long time, and its entirely possible that much has changed from 1965, so I stand to be corrected!!

I'll bet Colin Stafford has the correct answer for this.

Gord Clark
Rockburn, Qué.

Gordon A. Clark

hello, there are a couple of permatex sealant products that are impervious to fuel that might be useful to hold the "o"-ring in place. regards, tom
tm peterson

Gord Clark, I think David is correct, especially if ethanol type gasoline is expected. Buna N will swell using ethanol, and to put a finer point on the issue, it should be Nitrile F or GF, as there are several types of Nitrile.

Dallas
Dallas Congleton

Hi all

I have been using this solution for about a year now. There is no sign of the rubber perishing or disintegrating. I do think it has swollen lightly, but not by much. I filled the tank yesterday and opened the cap carefully, not in my normally brusque manner and the ring did not fall out.
I think the tank still vents properly because the ring acts a an extra sealant round the rim of the filler hole and I presume the venting goes round the side of the spring loaded inner part of the cap. I haven't had any problems whatsoever with fuel starvation.

David DuBois - the 40mm is the outside diameter of the ring.

Regards

David
David Wardell

To All,
Check with Mcmaster-Car ,, http://www.mcmaster.com/
enter O Rings in the search box,, they have all sizes and materials !!

SPW
Steve Wincze

Hello Everyone,

For the past 30+ years I have been in the Fluid Power business (Pneumatics, Hydraulics, Vacuum)... That being said, I have had a lot of exposure to various seal materials and their application limits...

The following should be helpful:

Buna N (Nitril) (NBR) - Excellent with petroleum products. -65F to +250F. Superior in compression set, cold flow, tear and abrasion resistance. Inferior resistance to ozone, sunlight or weather. Recommended for: General Purpose, Petroleum, Water, Diester, Water-Glycol... Not Recommended For: Halogenated Hydrocarbons, Phosphate Ester, Ketones, Acids, Brake Fluid.

Viton - A linear copolymer of vinylidene fluoride and hexafluoro propylene (approximately 65% fluorine). Compatible and recommended with most fluids and gasses. -20F to +340F (to 600F for short periods). Recommended For: Petroleum, Silicate ester, Diester, Halogenated Hydrocarbons, Most Phosphate Esters... Not Recommended For: Keytones, Skydo 500, 7,000.

The bottot line is - Both Buna-N and Viton are recommended and will work with exposure to gasoline (sorry mate, "Petrol")

Cheers,

Rod Macleod - TF 1500 HDB46/6798 ("Moll")
Rod Macleod

Why not buy a larger diameter seal and install it in the groove where the original cork seal is supposed to fit?
Jim Merz

Jim - Quite a number of years ago a set of viton 'O' ring seals were sold as a cure for all the usual fuel leaks on the T series cars. The kit included a large 'O' ring and a packing piece as a replacement for the cork seal around the filler tube. It was my experience that the 'O' tended to be pushed back as the cap closed, with the rear edge catching the seal first and bunching it up. If you take a look at a cork seal that has been in use for awhile, you will see evidence of this "bunching" tendency. Cheers - Dave
David DuBois

This thread was discussed between 23/09/2006 and 25/09/2006

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