tank sender sealing

[gjz30075]

Alex, how about filling up with enough petrol to cover the sending unit BEFORE putting the tank back in the car to check? Just siphon the petrol back out when finished.

Greg Z

[alexblack13]

Hello Greg.

Yes that's a fine suggestion and is more or less what I am planning but I am going to use parrafin as it's safer. I will submerge the tank sender and put a couple of lbs of pressure into the tank and leave it overnight to see if there is any leakdown... A bit like testing the head valves!

If all is ok (and it will be!) then I will go ahead and refit the tank over the weekend..

Still awaiting the parts from Sue but as I am working (2 days max / week ) Wed & Thurs' this week there is no rush..

Thanks to all for the great help & support..

Al' ....

[types26/36]

Alex,
If you are going to pressurize the the tank with a couple of lbs air pressure why dont you just spray a little soapy water over the tank unit and anywhere else you suspect of leaking, I did it with a tank that had been made for me a few years ago......sealed all the pipes etc. then pumped a few lbs in with a radiator tester and the soapy bubbles soon shows any leaks.......saves you filling and draining all the time.

[alexblack13]

Yes.. Good thinking there. I was going to leave it for a day or two under pressure but I think the soapy test would probably do it fine..

Thanks again...

[alexblack13]

Hey Nick...

Just had another good look at the sender unit mounting plate. The connection post looks fine but the plate it'self is 'dimpled' around the screw holes. They will need knocking back into shape before I refit it. That's about all I can see. Dimpling is not severe but will get attention anyway until it's as flat as I can get it..

Thanks for the heads up. I missed your post earlier...

Alex...

[alexblack13]

That's it all refitted and pressure tested. 1st test revealed two small leaks. Both of which were via the mounting screws. (Why Lotus? Why?... Blind holes please Lotus....) Anyhoo .... Out with the offending fasteners and re wrap with another turn of PTFE tape and... no leaks now!

Soapy bubble test works fine.. Good gasfitters trick this one.

I am tempted to take each screw out again and apply yet another turn of tape to each. They all have two turns of PTFE tape now and are slightly tighter in their respective holes. I don't think adding another turn of thread sealing tape to each fastener in turn whilst I still have the tank on the bench would be a bad idea.

Al'. .....

[William2]

I have just bought a new sender unit from Paul Matty (?48 + VAT). It came with a rubber gasket but I am going to use the cork type and use the correct sealing washers. Also going to use a light covering of Blue Hylomar either side of gasket.

[alexblack13]

[quote = It came with a rubber gasket but I am going to use the cork type and use the correct sealing washers[/quote]

?? Sealing washers??

AB

[TroonSprint]

On the MGB the sender is also on the side of the tank and it is sealed with a quarter turn locking ring and a "rubber" gasket. I've owned a few and never had any trouble with one leaking, even after removing it and replacing with a fresh seal. Mind you, there are no screws with holes open to the tank's insides....

My basket case Sprint came with a brand new stainless steel tank, and even that still has the screw holes going right through. It has a very natty banjo fitting for the fuel feed pipe connection, and a drain plug, and it is fully baffled inside. Superb. Why couldn't the screw holes be blind?

Mike

[alexblack13]

Good question Mike! An example of under engineering costing a fortune in Warranty claims.

A really stupid way to do it.. Most of the tanks at that time had the rubber seal ring and the quarter turn 'wedge ring to secure. It was foolproof! I had lots of those out and in in my time.. Never a problem.

No wonder the cars stink of petrol.

I am tempted to do a mod' whilst I have the tank out. Namely fitting blind tapped rivnut fittings with countersunk heads. I would need to drill out the st'd screw holes to approx 6 mm diameter and countersink them to take the rivnuts which would then fit flush with the tank face. Some sealant in the holes then and fit the rivnuts which take M4 fasteners at the correct length. The screw holes would then be sealed off and no fuel could escape along the threads, so no faffing around trying to seal the screws. Tempted as I say. I have the rivnuts in stock too..... If it were not for the issues regarding working on a petrol tank I would get stuck in.. Hhmmmm....

Intrigued with regard to Will2 's ''proper sealing washers'' Will? Care to explain?

I have a set of small diameter (3mm) Doughty type washers with built in rubber seals, but fitting them below the st'd hex setscrews I don't think would work. not enough of a 'flange' on the fasteners which dont sit well on the rubber seals! Oh well ... Perhaps Will' can fill us in? I could be missing something.

[elanner]

Alex,

I think that there's a risk of over-engineering this or, put another way, ignorance is bliss.

When I did mine last year I had no idea that the screws could be a problem. When I took the old sender out I saw that the screws had been fitted with fibre washers. But there was crusty old sealant gummed around them so I chucked them out and got some new ones (in the US getting non-metric washers is easy).

I realized that petrol was going to run up the threads but figured that as long as the washers provided a seal it didn't matter. Of course, the cork gasket also needs to provide a good seal around the screw hole. I didn't think of using PTFE tape (and for some reason always make a hash of using it anyway). I just assumed that the washers and some goo would do the job. And they do.

I had 2-3 of the screws leak so I simply tightened them all up a turn or so. That was that.

I did think the design was rather hokey, but I'd never done any of this before so assumed it was standard practice. A side mounted sender seemed daft enough to start with, so why worry?

Nick

PS: When I bought my first house, many years ago in Blighty, I did some plumbing (central heating, no less!) and always screwed up PTFE joints. So I used horse hair and plumbers putty. Now that stuff WORKED!

[TroonSprint]

I'm surprised that PTFE tape is petrol proof. I was thinking of using some silicone sealant on the threads when I get round to installing the tank. But is that petrol proof? I have this stuff from Toolstation (http://www.toolstation.com/shop/Adhesives+Sealants/General+Sealants/High+Temperature+Gasket+Sealant+310ml+Red/d180/sd2350/p66124) and I've used it extensively on my MGB V8 and it is excellent. But is it petrol proof, that's the question.

While we are chatting about this subject, what size and thread are the six screws that hold the sender in the tank? I don't have any at the moment.

Mike

[alexblack13]

They look like a BA screw, but never checked!

It is a real PITA this silly problem and is partly down to the type of screws. They are just a very small hex head and difficult to get a seal on using either fibre or Doughty (Dowty) type sealing washers. And you need to remove the spring lock washers if you try using a sealing washer of any kind.

The reason I thought about taking the screws up to 4 mm are.. I have them in button heads and the heads are just over 7mm in diameter and the undersides have a decent surface both in finish and in area to sit well on either type of seal and just perfect for the 4mm dowtys I have in stock. That would fix the problem without going nuts and remove the hit or miss, is it sealed? Yes it looks ok, and a few weeks later you have a leak again... I have been here with this already. So if it needs taking out again for leakage down those fecking screws then I am going to retap and try the 4mm screws with sealing washers 1st. If that doesn't work I will 'blind' the holes with the rivnuts mentioned earlier... Over engineered? Well so be it!!

The tank is back in and re-filled and so far so good & I am quite confident it will be fine.

PTFE tape I am assured by my Son is petrol safe. He is an Opps tech' with Shell on Brent Bravo production platform and is currently second in command, so that will do me.

Silicone sealants on the other hand are generally NOT petrol proof unless you buy the correct type.. 3 Bond for EG is perfect. I sealed the screw threads with this to start with but still had a little leakage.. I think most of it was removed when screwing the fasteners in. Hence the now well PTFE wrapped screws. Looking good so far. But will keep you all posted.

Many thanks to all for the great input and suggestions.

Alex...

[elanner]

Ah! "....very small hex head and difficult to get a seal on...."

Mine are a decent size Phillips head. So there was no problem getting a seal - once I'd tightened them properly. There were no lock washers. Of course, after all this discussion it will probably start leaking now.

Nick

[alexblack13]

An example of the bitterness of poor design & quality remaining long after the sweetness of price (& weight?)
is forgotten.....

I thinketh so...

Those little screws are very small. I think no more than about 3 mm or so diameter. but never checked. I just looked at the threads for wear etc...

Nick .. Its possible your fastener holes might have been bored out a bit. A decent head diameter would be a def' advantage and make getting a seal possible. One would have to be careful not to over tighten the screws though as this could damage and extrude the cork gasket. Small shims fitted into the gasket holes would cure this. Allowing a good tighten of the fasteners and not over tightening and damaging the gasket.

That 3 bond sealant it the muts nuts by the way.. I then discovered it is exactly the same as the Hondabond engine build product... And ..... I had a (Old ) tube of that in my box... Oh well! It was past it's best anyway.. Lol...

Alex...

Al ' .....