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MG MGB Technical - Fuel Tank removal -stripped thread



I have had the odd wiff of petrol from the rear of my BGT, so given the time I currently have thought I would drop the tank to have a look at the top – all being well a wipe over with some Waxoyl to the tank top and boot floor and one less thing to worry about.

I thought before I got too far just check all the nuts and bolts would move – they all do apart from one. It is one of the ones that the nut comes off from the bottom and there are 2 issues:

- It is a nyloc, 12.6mm across the flats so the ½ in socket is a bit too big. I reckon I can get round that with some bolt grip removers? Luckily it did not come off …..

- The threads of the stud that protrudes through the boot floor are shot so how do I deal with that? Is the stud welded in?


Seemed like a simple job an hour ago. It would be good to sort it in case I have to get the tank out one day, if not this month, as no doubt it will be an issue the day before a trip, or as was the case with my midget the day of the trip.
Mike Dixon

Mike,
unless someone has put an odd nut on it should be 5/16" thread that needs an 1/2" spanner/socket.

Nylocs are fine, possibly better than split washer and plain nut but mostly plain nuts were fitted so again it might suggest that nut at least has been changed.

What makes you think the threads are shot, could you not clean them up, brush clean then use a couple of the correct (plain) nuts to reshape the threads. Run the first nut up and back, turn other side up and repeat, throw it away and do the same with second nut. If you can thread a third nut up and back with just using your fingers then its all good.

Otherwise yes they are welded-in.

This assumes you have the later tank as your profile doesn't show the B.

If you lower the tank check for packing strips (usually rubber) and that they're fitted the right way round.
Nigel Atkins

I suspect the nut is a half inch but severe corrosion has reduced it by a gnat's whisker, so your 1/2" socket just spins making the nut worse. Is that right?

For severely rusted nuts the traditional 12 point sockets are not much good as they will round off the corners. I have a set of wall drive sockets that can cope with just about anything. One set covers both metric and UNF/UNC. I also have a 2 foot long, 1/2" drive, breaker bar and not many nuts can resist that. The danger with a 5/16" thread is that you could snap it, so with my long bar I would get it to turn just a tiny amount then retighten, and keep doing that. It will give up eventually, although it could be tight right the way down the thread, even with penetrating oil.

How do I know this? Long experience reinforced just today as I was undoing the nuts on the leaf spring U-bolts. They were nylocs too and they fought me all the way down the thread, but I won.
Mike Howlett

Yes the studs are welded in from above the boot floor, those are handy to hold the tank while you are dealing with the remaining nuts and bolts. I wouldn't worry about shearing a stud, once the tank is out that will be easy enough to deal with. I've wedged oversized spanners on hydraulic fittings using a 1/2p coin in the past, I'd be trying similar with a socket as well as trying every socket and spanner at my disposal. Sometime a slightly undersized one can be forced on enough to undo. If all else fails I'd drill or grind the stud off from inside the boot.

Not long after getting my roadster I just happened to touch a lower front corner with a spanner working nearby and saw a stain slowly spreading from that point, must have been tissue thin. Obviously a 'panic' job with nowhere to store more than half a tank, I was lucky in that all the nuts and bolts came undone so I could prop the tank on one end outside until I got a new one and properly painted and treated it.
paulh4

Thanks - I like to have a disaster recovery plan in place before I set off!

I have tried metric and Whit as well as AF and no luck - the 1/2 inch is over a mm out, to mix my units. As you know there is not enough space to get molegrips/pipe wrenches or even a nut splitter on it, not helped by the fact the nut is embedded in the fibre washer. I will try the trick with something jammed in the socket but might these work

https://abtoolsonline.com/3-8-drive-shallow-bolt-extractor-remover-removal-set-1-4-1-2-5pc/


The threads look like someone has taken a file to the them - the stud is all but flat on ones side, so I think the stud will have to come out anyway - I would rather do it without the tank in there - but it would save me faffing about with the nut?

Luckily it is the rear one so if all else fails I can put a bolt in there as I can reach both sides at the same time. Not for the purists, I did wonder about gluing a stud or even the bolt in there as I do not have a welder.

Mike Dixon

Sorry Mike I totally misunderstood I thought you'd got the nut off.

I've no idea about those extractors work well or not, they might be just the ticket. Whenever I've bought special tools for just one job I've found they've not worked on that job and I have the alternate dilemma of having bought cheap or bought expensive and then never ever using them again, I once bought three standard tools in a size or type I didn't already have to get a small nut off and none of them worked and I've not used them on any other job since (a mate helped get the nut off by using confidence and brute strength).

Both techniques suggested by Mike and Paul I've used and combined or get a slightly undersized sacrificial socket and hammer it securely on. I've never had any problem snapping studs, when I've wanted to or not.

As always, apply a good penetrating/releasing agent (not standard WD40) and leave to soak for as long as possible (overnight or longer) then first try to tighten to break the rust crud (fibre washer) seal then try to loosen. If this fails repeat the whole procedure, allow plenty of time and patience and for the chemicals to do the hard work.
Nigel Atkins

Unless those extractors are the right size for your nut I'm not sure they will work. You could try a 'universal socket', never used one but they have a set of pins some of which get pushed put of the way to leave others round the nut.

Cutting the stud out with the tank removed would certainly be preferable, and if you don't mind a bolt head in the boot and a nut underneath that's fine. As I recall half the fixings are bolts anyway, going to captive nuts on the edge of the tank - nut-retainer 34G 523, so you don't need to get to both sides at the same time anyway.
paulh4

Incidentally this shows a captive nut and bolt on the left, and a stud and nut on the right.


paulh4

Mike, the extractors look very similar to an an Irwin set I have and they work very well, you could also try a set of Metrinch sockets.
R.A Davis

I thought about those universal sockets with the retractable pins as I was lent one once but I can't remember if I tried to use it it or not so don't know of it was any good or not.

Super Grip Universal Socket - https://www.ebay.co.uk/itm/233814662915

If there's enough room perhaps a 'Super Wrench' might work because of its spring loading where clamp hasn't.

I bought a set of four 'Super Wrench' at an NEC show decades back and I've only successfully used them a couple of times where other more conventional tools failed. They are good on removing round and square tubing where marking up doesn't matter but I've never needed that use.

https://www.ebay.co.uk/itm/383955557731

Not my set in photo, mine are still shiny, but those from eBay listing.

Second photo from other eBay listing.






Nigel Atkins

I've got a set of Super Wrenches and in all the years I've had them I've only found a use for them a few times, most times I've tried to use them they're too bulky or they just don't grip sufficiently. My favourite if I need to grip rounded nuts is an old Top Speed Wrench, it was made in Japan and if there's enough room to use it, it's never let me down.


R.A Davis

Rob (Mike),
apologies, I missed your post (making much of mine redundant).

And I'd have finished mine sooner had I seen your post or been able to remember the sockets were called Metrinch.

The Top Speed Wrench looks perhaps better built but without your post I'd have thought they were the same thing as the Super Wrench.

Seeing a link to Top Speed Wrench perhaps Mike might possibly be better in this case with the SW version. - https://www.toptools.co.jp/english/products/193/



Nigel Atkins

This thread was discussed between 18/02/2021 and 19/02/2021

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