Sealing the deal

Mechanical Meditations

A few posts back I had Rusteco purge the MB5's fuel tank of 28 years worth of rust. The procedure was a success, but removing all that iron oxide left quite a few pinholes, and that bare metal is awfully susceptible to corrosive coastal air. Brazing the holes would only take care of the openings I could see and wouldn't do anything to protect the exfoliated steel, so I decided to kill two birds with one stone and seal the tank. My internet search led me to the Caswell site ( where I found a two-part epoxy tank sealant kit for $39.99

Of the various products available, Caswell’s two-part epoxy sealant is supposed to have the strongest bond (I read forum posts about other sealants peeling off after time) and be the most chemically resistant. It works on metal, fiberglass, and plastic tanks, and the kit comes with enough material to coat two 5-gallon tanks or one 10-gallon receptacle. After plugging the petcock hole with putty, taping over the pinholes, and sealing the tank opening with Seran wrap, I mixed the components in a small tub and poured in the concoction. Using the stuff is as easy as stirring Part A with Part B together, but the instructions insist that the ambient temperature be between 70 and 80 degrees.

Evidently 69 degrees isn’t close enough to 70 degrees, because the sealant flowed like cold molasses. That’s my bad; I was impatient and wanted to get the project done before work instead of waiting until the air was warmer in the afternoon. I tilted and shook the tank for the better part of an hour to get the inner surface entirely coated, and then I had to keep rotating as the epoxy cured so it wouldn’t puddle. It was a pain, but the plus side is that the slow-flowing fluid created an extra-thick coating. A day later the liner is fully cured and barely scratches when I scrape it with the blade of my pocketknife. Not only are the holes plugged and the bare metal protected, but the rock-hard sealant also serves to bolster any compromised areas of the tank walls.

Now that the interior of the tank is fully restored, I’ve allowed myself to think about the exterior. I’m envisioning a Freddie Spencer/NS500 tribute. The MB was introduced in 1982 – a year before Spencer won the GP on an NSR500 – and I think it’s safe to assume that every teen with a Mighty B must have idolized Fast Freddie. There isn’t much room to work with, but I think I can incorporate that famous red white and blue striping.


Caswell Plating
Epoxy tank sealant 70cc kit

Perk LLC -Case gaskets and technical advice. Supplier of hard-to-find moped parts. (317) 371-8530

Rusteco-Rust removal treatment for the MB5's gas tank. (800) 787-8326

Haynes Manuals
-Invaluable technical information and diagrams.
(800) 242-4637

Huntington Beach Honda
-Various OE parts such as gaskets, grommets, and seals.
(714) 842-5533

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