Gas cap seal while cleaning a tank

I’m working on two nastily rusted tanks from a ‘75 CB125 and a ‘81 CM200t. Both were super rusted but I’ve gotten the bulk of it removed with a combo of vinegar, bolts/nuts, lots of shaking and some experiments with electrolysis. I’m now about to do a final bath in evaporust and start the procedure for a Por15 seal.

The thing I keep having trouble with is sealing around the gas cap to avoid leaks while rotating the tank around. When it was vinegar, no big deal, but I’m hoping to reuse the Evaporust as much as possible. I’ve tried plastic wrap and rubber gloves around the cap, but they just tear when I turn the cap tight.

Do you fine folks have any suggestions?
 

pidjones

Well-Known Member
Might try inflating something in the opening instead of using the cap. Balloon, rubber glove, tied-off inner tube, plumber's plug.
 
Thanks guys... great tips. Would the expanding plumbers plug work on a tank opening that has the two notches?
 
Last edited:

Maritime

Well-Known Member
Thanks guys... great tips. Would the expanding plumbers plug work on a tank opening that has the two notches?
not buy itself but a couple pieces of rubber fit in the slots first then the plug should do it. Make them fatter than the slots by a little so the plug pushes them in and should seal up.
 
Have you replaced the gasket on the fuel cap? If it's just a drip, I'd put a bucket under it to reclaim the evaporust and call it good.
 
Yes, the vent leaks and it's also a super old gasket.
I should have checked this thread and used your idea of extra pieces of rubber. In the mean time I used Ichiban's suggestions of the expanding plug and added some Thermal Adhesive Plasma to seal up the notches. It's working for now, but I'll use rubber pieces for the next tank.
GasTankPlug.jpg
 

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