Petrol tap threads

[tippy]

Hi all, I have a problem with a petrol tank!  I have just come to refit the petrol tap but the threads in the tank where the it screws on are now almost non existent!  I did not notice the issue when I removed the tap.

F2 petrol tank, anyone successfully repaired any of these? 

Thanks in advance.  Tip

[4l04ever]

You could try tapping to M7 and drill the tap out to suit, but that would only give you 0.5mm of thread on each side if all the original thread has gone.

[tippy]

I don’t know if I dare try it!

[midlifecrisisrd]

When you say non existent do you mean the threads are gone or that the plate the threads are in are really thin

The plate the threads are in is only about 2mm thick

Steve

[tippy]

Hi, the plate is fine, the threads have all but disappeared. I’d had some work done on the tank and it must have somehow damaged th threads.

[4l04ever]

You could get the holes partially welded up then redrill and re-tap.

[lcmarky]

Send a tap through first, you may be surprised what it recovers.

[steve63]

It depends what stage you are at with the tank. It would be better if it's not painted yet. 

if it were mine and the threads were gone or nearly gone I would either put a couple of M6 nutserts in and weld them or make/have made some bar tapped M6 and weld them in. When waiting for something to be machined is not an option I've had success rounding the points off nuts, opening out the holes to accept them and welding them in. Never on a tank but on box section where I wanted something stronger than a nutsert.

[jon]

I think I would go about this in a different way. I’d make a new thick flange with new threads and clearance in the centre for the fuel filter. Dangle some cotton with a small weight on the end through the petrol cap hole and out the petc**k hole. Snap the weight off and tie it round the fuel filter. Push the petc**k into the tank and use the cotton to guide the flange into position. Screw it all up.

Jon

[tippy]

Apr 3, 2024 12:53:05 GMT 1 steve63 said:

It depends what stage you are at with the tank. It would be better if it's not painted yet. 

if it were mine and the threads were gone or nearly gone I would either put a couple of M6 nutserts in and weld them or make/have made some bar tapped M6 and weld them in. When waiting for something to be machined is not an option I've had success rounding the points off nuts, opening out the holes to accept them and welding them in. Never on a tank but on box section where I wanted something stronger than a nutsert.

Its painted and all lovely, I barely dare touch it as it is!

[tippy]

Apr 3, 2024 19:14:55 GMT 1 jon said:

I think I would go about this in a different way. I’d make a new thick flange with new threads and clearance in the centre for the fuel filter. Dangle some cotton with a small weight on the end through the petrol cap hole and out the petc**k hole. Snap the weight off and tie it round the fuel filter. Push the petc**k into the tank and use the cotton to guide the flange into position. Screw it all up.

Jon

This I like!

What I have actually done is took it to a guy who is confident he can fix it.  I will report back when I have it in my hands!

I actually have another tank with a different problem that this might end up coming into play on!

Tip

[steve63]

Apr 3, 2024 20:10:19 GMT 1 tippy said:

Apr 3, 2024 12:53:05 GMT 1 steve63 said:

It depends what stage you are at with the tank. It would be better if it's not painted yet. 

if it were mine and the threads were gone or nearly gone I would either put a couple of M6 nutserts in and weld them or make/have made some bar tapped M6 and weld them in. When waiting for something to be machined is not an option I've had success rounding the points off nuts, opening out the holes to accept them and welding them in. Never on a tank but on box section where I wanted something stronger than a nutsert.

Its painted and all lovely, I barely dare touch it as it is!

Oh, well that narrows down your options a tad.
In that case I would probably stick a screw in it to judge how much and how good the threads are then either stick the tap on as it is or if the threads are past it then maybe give the 7mm tap a go as suggested. I've never looked at buying M7 screws before though. Second option is M6 nutserts. You can get them with a tiny countersink so they finish almost flush and the o ring on the tap should hopefully prevent leaks. I may even have some if you are stuck. Best of luck.