Moss Viton sender unit gaskets - a warning!

[RobThomas]

A Metric, post-Brexit dozen.

[Napoleon Boot]

A Metric, post-Brexit dozen.

Right, take two; I've ordered a cork gasket and 'uprated' gasket from Bull Motif.
(these: https://www.bullmotifspares.co.uk/searc ... r%20gasket)

What is the best method of fixing either of them - sealant or no sealant? I'm not sure if the cork gasket is impregnated with rubber. And should I also look for some nylon washers for the machine screws holding the sender unit in place (which are 8-32 UNC apparently). Or can I put a blob of sealant on them? Is that asking for trouble?

My original problem was that a full tank always led to a very smelly car, and a puddle of fuel on top of the tank. The original paper gasket, refitted with Hydromar Blue, is doing a good job at the moment, with no whiffs or leaks, but it's not in the best condition and I'd like to do the job properly before putting the floorboards back down again.

[RobThomas]

Cork gasket alone should be fine. Shouldn't really need a sealant if the surfaces are flat and smooth. Hylomar might help the paper to be fuel-proof, though.

I think the screw holes are sealed at the other end with steel, but I might be wrong.

[biomed32uk]

Cork gasket with a wipe of Hylomar worked for me, the screw threads need to be sealed with a fuel resistant sealer - I used Bondloc B577.

I was getting the smell of petrol with it creeping up the screws which I get no more, the Bondloc has been there for 18 months now. Has a multitude of other uses as it is a thread sealant and is very resistant to car fluids.

[Declan_Burns]

Cork gasket alone should be fine. Shouldn't really need a sealant if the surfaces are flat and smooth. Hylomar might help the paper to be fuel-proof, though.

I think the screw holes are sealed at the other end with steel, but I might be wrong.

Worth checking if they are really 8-32UNC and adding the result to the list of threads. I have my doubts! There was a long discussion about the threads used on these sensors on the MG forum. On the MG TD they turned out to be 3BA and Moss had been selling the wrong screws for years and all sorts of problems arose. Also worth checking if the cork gaskets are silicone impregnated. Silicone is not fuel proof. Ask me how I know when came out (on my way to the pub) and I saw petrol flowing out under the garage door. I didn't make it to the pub that evening.
Regards
Declan

[philthehill]

8/32" UNC = 1/4" UNC which has a TPI of 20.

[Declan_Burns]

I doubt if 1/4" UNC screws would fit-far too big.
Regards
Declan

[pgp001]

8-32 does not mean 8 x 1/32"
It is a number 8 and is 32TPI the OD is actually 0.164"

Assuming you were not having a laugh. Hope this helps
Phil

[philthehill]

Not having a laugh.

I do not identify 8-32 as a recognised way of describing the bolt/screw so what thread is being described this way?

3 BA has been mentioned but I have a full set of BA taps and 3 BA does not conform with the number of TPI (32).

Phil

[RobThomas]

From a Jaguar thread...

Neville: Spending a few minutes with the Parts Book reveals that the tank "element unit" securing screws are Part No. AS.303/4H. This number shows up in the Standard Parts section under "Setscrews" as having a "3 BA" Thread. It also indicates that there were only two other "cheese head" screws that same size used elsewhere in the car (8 total). The alloy cars used 20, 1/4" countersunk "3 BA" thread screws on the "windscreen tapping plate"? I hope someone else on the list can translate "3 BA" into a more recognizable tap size for us. Good luck, Dick Cavicke

Neville, There are six screws holding on the sender unit. The original thread is not available in the US, I believe it is 8x36x1/4". I use a stainless steel fillister head 8x32x1/4" as a substitute. All you have to do is run a 8x32 tap into the holes, and they will accept the new screws. If you can't get SS at the local hardware store, you might be able to get brass, both will allow you to take things apart later if you ever need to. - Regards, Wray Schelin

I believe the screws are 5-40 (#5 screws with 40 threads per inch). I never could find a flat head brass replacement, but did find an allen head screw which fit correctly. You may be able to find a correct tap at an industrial supply house, like (if you're in the US) Enco, Grainger, or McMaster Carr. - Good Luck - Jag150

Assuming that they are 3BA (and I have not checked this), 3BA is 34.84 tpi and 0.1630" diameter (talk about standardisation!!). This happens to be a thread pitch of 0.73mm and diameter of 4.01mm, a standard 4mm screw has a pitch of 0.7mm, so a standard 4mm tap should do more good than harm. I got these numbers from Newnes Engineer's Reference Book 1951. Check the screw pitch against your 4mm tap before you put it in. - regards, Mike Morrin

Wray, Neville, One of the exasperating or amusing "charms" of the Jaguars from the transition period is the several different thread systems we must contend with. My FHC sports at least four, and possibly five or more if you get pedantic about it. They include: Whitworth, BA, Unified, Lucas' own spiral shapes, and some of the odd choices made by respectively Girling, Lockheed, Trico and Skinners Union. Although most can be easily bought from the UK, for the single car owner it is rarely worth it nor is the need frequent enough to stock all of the taps and dies for each of the variations, so sometimes a compromise is indeed warranted. However, forcing an 8-32 into a 34 pitch hole is to me too much of a "beat it to fit, paint it to match" approach. If you do not want to buy a modest set of the most common taps, a 4MM thread comes much closer to fill the 3BA thread form over the length of engagement than a -32 and it might even provide a more durable seal. - Regards, Klaus Nielsen

Klaus, No forcing required, the diameters are the same(.160"), only the threads are insignificantly different. I think there's confusion here, with the four smaller screws that hold on the small cover that is on the sender unit. I think Neville asked about the sender retainer screws, not the cover screws, which are something completely different. - Regards, Wray Schelin

Wray, I agree that forcing the slight (32 to 34+) difference will not make one whit of near term difference; but I just cannot bring myself to do it when better ways are at all possible. After all, we are talking about repairing/restoring rapidly diminishing resources and both BA tools and spare screws and nuts are still abundantly available from England. Just one guy's view......... - Still, best regards Klaus Nielsen

I have found the threads to be very close if not the same as 6-32 on the several XK tanks I have done... - Lee Eggers

Thanks to all wo have responded to my question.I have a 8nc -32 and 6nc-32 tap in my set, and as stated before, neither of them are correct. The 6--32 is a rattle fit.. After starting this discussion I got to admit that I do not think I have serious damage to the threads, the bigger problem is an accumulation of dirt in the bottom of the hole. I suspect the screws are bottoming out against the slug of dirt before pulling up on the sending unit. A can of WD40 and a needle may be all I need. - Thanks again Neville Laing

[philthehill]

Can somebody please simplify the numbers in the post above i.e. what is a #5 screw?

There appears to be no reference to the type of thread used with a #5 screw.

I am usually pretty good on threads but the descriptions have me totally confused.

I have a very good selection of taps, dies and die nuts but I do not possess a #5 tap, die or die nut.

Clarity is what is needed.

Phil

[paul 300358]

Phil
See https://www.boltdepot.com/fastener-info ... s-tpi.aspx I still don't know, but then will the Americans understand all our sizes?
Paul

This is better https://www.boltdepot.com/fastener-info ... meter.aspx

[philthehill]

Paul
Many thanks for the link.

American National Coarse A.N.C. 60 degree thread flank.

I had an inkling that the describing of the threads may be from the other side of the pond!

I am not aware of any ANC threads on the Morris Minor/1000. UNC yes.

Phil

[Napoleon Boot]

Cork gasket alone should be fine. Shouldn't really need a sealant if the surfaces are flat and smooth. Hylomar might help the paper to be fuel-proof, though.

Thanks Rob, I'll give the cork gasket a try without any sealant and see how I get on; both surfaces are clean and smooth so hopefully that'll work. If not I'll check there's no rubber inpregnated, and use a bit of Hylomar and Bondlok for the screw threads.

I do not identify 8-32 as a recognised way of describing the bolt/screw so what thread is being described this way?

Sorry for opening a can of worms here! I find that a very odd way of describing it as well, but that's how I've seen it written I've read on various threads (no pun intended) and also on Holden's website:
https://www.holden.co.uk/p/spare_parts_ ... r_set_of_6

I have read about lots of folk getting 3BA screws and then finding they don't fit, and vice versa. Luckily I don't need any new screws at the moment (until I inevitably drop one into the tank next Saturday ) but it's weird how difficult it is to find out what size these screws actually are! I guess it also depends on whether the tank and sender are original equipment or a modern replacement...

[philthehill]

The Holden link states 8 x 32 UNC (Unified National Coarse). It was the lack of UNC (or thread style) in the post above that was confusing.