Could someone confirm the size of the fitting at the main tank for the expansion tank return line? First time pulling a fuel tank. 1/2" too small, 9/16" too large; 13mm too small 14mm too large. What the heck! Sorry just can't find my adjustable wrench at the moment and curious.

 

That sounds wrong - I have both types, one of which is on my desk right now - one is 14mm and one is 15 but that's in the garage so no pic at least till tomorrow - apologies I'm lazy ... the tanks changed but not sure when - either way a 9/16 too large - ... somethings not right

 

Do you mean this part?
https://www.ebay.com/itm/384850662143

If so, I think the threads are UK pipe sizes and I think the hex on the fitting is Whitworth!

 

Interesting part description but I think that is the right hose. Whitworth fitting, good lord haha =) Would a regular set of Whitworth wrenches work on the fitting? It looks like 1/4" Whitworth might fit right between 13mm and 14mm!

 

Just what are we describing as an expansion tank - do you mean the little tank below the main tank in the back of the car ? there is only one pipe in the back with a thread both ends and that isn't the one on ebay - there is a short one on the return line from the engine to the fuel tank - threads into the tank and also a 90 degree fitting.

Are we at the front of the car or the rear - that pipe I showed is the swirl tank to the main tank only one end of it has a thread (I actually think it is only a bleed to ensure the swirl tank is fully flooded) - I also have the return line from the bottom of the boot (trunk) 90 degree fitting which has threaded fittings both ends - the 90 degree fittings are I think SAE - 9/16" x 24 tpi - my old tank is the same. My new tanks threaded fittings are M14x1.5. Some tanks had a threaded feed from the tank to the swirl tank but my tank doesn't so I know nothing about the size of that one - only know it is a 10mm ID hose.

A high end set of Knipex 8601 will solve the problem I have the 250mm and they're an absolute go to for oddball stuff.

Knipex Pipe Plier

 

Yep expansion tank=swirl tank I think and it is the return line not the supply line that comes from the bottom center of the main tank. You are right it only threads into the main tank[the fitting in question] and pushes onto the top of the expansion tank and must just be to bleed air allowing it to fill..

 

This pipe is to enable the swirl/sump tank to bleed back up to the airspace at the top of the main tank. You can still buy Whitworth spanners. He, Whitworth, was a very interesting man a true Victorian polymath. The first person to measure accurately to one millionth of an inch and to standardise thread sizes and to design the thread profile precisely. A very interesting man from an age when people got stuck in and did things, unhampered by too much useless 'education'.
https://en.wikipedia.org/wiki/Joseph_Whitworth
The only other Whitworth threads that I know of on the XJS are the firewall post fixing nuts!