Leaky glass-fibre tanks

[jerry thurston]

I have recently had to repair a glass-fibre petrol tank with a slow but persistent leak.

The main problem is that because we use all premix there is oil residue everywhere and the resin won't stick.
I reckoned that the leak could do me a favour here, so I sloshed some brake and clutch cleaner in to clean out most of the petrol/oil and tipped this away, then filled the tank with a couple of litres of the cleaner and left it outside to gradually leak until empty, then I did it again... The slow flow of the fluid seems to have scoured the leaking area perfectly clean. Then I left the tank to dry thoroughly for a couple of days.

I removed the previous patching to reveal the hole that had been mended before roughing up the face with a hack saw blade and new wire brush, once satisfied that there was no oil still present in the weave I re-glassed the area.

Mixed a little more resin with a small amount of hardener ( just enough to make it set eventually but to keep it liquid for as long as possible )and poured it into the tank making sure that I didn't block the holes in the baffle. Slowly tipped the tank this way and that to move the resin around the edges of the tank and over where the hole had been mended. Sure enough to start with it dripped slightly in a couple of areas where the bottom was de-laminating where it was attached to the top.

I only stopped tipping as the resin started to set and became immobile.

24 hours to dry thoroughly and tried more brake cleaner (as this is very searching and should reveal any tiny holes).

It's dry!

Only time will tell if this cure is 100%, I'm confident that it is... But you may mock me if you spot me in the paddock with fuel and oil dripping from every crevice!

[bultaco49]

Hi - If your leak cure doesn't work there is a good repair kit available from Casewell Europe, link here
caswelleurope.co.uk
Enter site, scroll down to 'Repair Products and Paints' and look for 'Petrol/Gastank sealer'

I have been rebuilding and restoring Bultaco trials bikes for a few years and the early ones had fibreglass fuel tanks. I have always used Casewell for repair and sealing new tanks and have never has any problems. I would advise any one who purchases or makes a fibreglass tank to seal the tank before use as additives in modern fuels will attack the resin and the seams may eventually leak. Many other tank sealers such as POR15 are not suitable for fibreglass.

Best cleaner for tank residue, including 2t oil, is acetone. Careful if your tank is painted though. Acetone will attack paint.

Tim