I made the stupid mistake of cutting the hole in my fuel tank (for the gauge sender) in the wrong place and, although the sender is now in the right place, I'm faced with an unwanted hole in the tank.

It's a plastic tank, and I tried using the piece of platic cut from the correct hole, which was slightly bigger then the first hole, and sealing it on with SikkaFlex. This looked like it would do the job until I filled the tank with fuel when it started to lift off. I assume the fuel vapour has attached the sealant.

So my question is how to seal the hole permenantly without needing to replace the tank. The hole is in the top of the tank on a Fury so will not be accessable when the body is fitted.

Make an oversive cover out of suitable material (same sort of material as the tank, aluminium, etc).

Drill some bolt holes around the outside.

Put some rivnuts in

Bolt on cover using a suitable gasket to seal between the 2 items.

well you deff need a good sealant...

i thought window glue/sealent is good enough....

Db

You could also try using a soldering iron to weld the 2 pieces together...

Are you sure you haven't got one of the infamous leaky plastic tanks that will need replacing anyway?

Obvious to say it but... don't put any naked flames anywhere near the tank or the hole. Use an electric soldering iron if you must but if it was me I'd be looking for a mechanical fix.
BTW my local (proper) accessory shop stocks cork composite sheets which make good gaskets for just your type of application.
Cheers, Pewe

I have a plastic tank in my boat and the unused holes in the top are just covered with some thicker plastic, cork gasket held on with stainless self tappers.

Buy some Blue Hylomar.

Make a circular plate to cover the hole (alloy plate will do), rivet it on with at least 6 equally pitched holes, and assemble with Hylomar. Dip the rivets in Hylomar before you insert them. Use the softest ally rivets you can find so they actually form inside the tank and don't just stretch the tank material as they form, and end up pulling through....

Cheers,

Rich.

stop!!!!!!!!
you need to use 3mm ally plate as a cover over the hole - allow an inch overlap and bolt thro with ally rivnuts

use ONLY 3mm nitrile rubber sheet right across the hole IE the exact same shape as the cover plate with no hole in the middle just the holes for the bolts

put bolts every 1 1/2" - use 6mm bolts in stainless

do em up tight and make sure the mating sealing face is clean, not scored etc..

there is no permanent mastic type stuff - been there trying to seal my inspection cover up - worked wonders when i went to a gasket manufacturer - they told me the ONLY way to do it

petrol will dissolve hylomar eventually and PU adhesive

dont use thinner ally cos it will distort as you tighten down tight

take care with the hole drilling not to slip or to oval the holes and remove ALL burrs from the top face