What mastic to bed a nitrile gasket and s/s lid to inspection hole in diesel fuel tank?

[Mudisox]

Having cut a hole in the top of my fuel tank, cleaned it out and secured small bolts with large s/s washers in holes around the edge of , the tank, I am left with a quandary as to what further bedding compound I should ensure that the diesel will not contaminate the fuel but fill in any gaps to seal the 3mm thick lid.
The 60 litre Tank is made of only 2mm s;s with a baffle welded across halfway and this has slightly distorted the top. Gasket is 5mm nitrile sheet. Holes with bolts are 30mm apart and secured with epoxy. [thread did not take in the thin metal.]
Silicon goo? or what.

 

[captainboo]

I sealed the stainless steel circular lids to my stainless steel tank using a 2-3 mm cork and nitrile gasket and Loctite flange sealant I got from Halfords that was suitable for diesel. The bolts round the edge were also about 30mm apart screwed through the tank top from the inside and then the lid bolted to them. They have never leaked for the last 10 years.

This stuff:- LOCTITE MR 5922

 

[tillergirl]

No bedding necessary if the gasket is sufficiently substantial.

Image1 by Roger Gaspar, on Flickr

The gasket was at least 25mm wide and the lid was bolted down. Nothing leaked in 28 years of ownership.

 

[goeasy123]

Blue Hylomar for anything hydrocarbon.

 

[Iliade]

How about adding a reinforcing ring inside the tank to prevent it bending when you tighten up the bolts, or rather to help it flatten out. You could also thread the holes (in the ring) or weld the bolts so that they are captive for when you want to look inside again.

No sealant should then be required.

 

[tillergirl]

Good point Iliade! I didn't point out there is reinforcing square inside the tank and that is why the gasket performs correctly.

 

[Moodysailor]

You should not need any sealant with a suitable gasket, which it sounds like you have.

 

[rogerthebodger]

On both my diesel and water tanks I used a steel / stainless steel cover on to a rectangular hole.

I made up a internal frame from 5 mm thick stainless with M8 studs threaded into the internal frame held in with sikaflex.

The lid and the tank had matching holes with a 5 mm thick neoprene foam gasket There is no sealant between the top of the tank and the lid and I have had no leaks in 10 years of use.