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Tech Tips Vol 2 Top
The chrome on these flip-up caps holds up pretty well over the years but the spring loaded seal hardens and cracks. Often its metal disc holder and especially the rivet head that holds it in place rusts badly. In this case, the holder was okay so I replaced the seal with a modern polyurethane one, and the rusty rivet with a stainless bolt. After removing the cap from the tank, the first step is to carefully drill out the head of the retaining rivet. Use an oversize, sharp bit and the seal/holder will pop out once you’re through.
ou can now lay out the components. Don’t lose the small "rubber hose" spacer which goes on before the disc holder. If reusing the holder, Scotch brite and a dab of grease will help keep it from rusting. If it’s too far gone, new disc holders with integral neoprene seals are available from many British parts suppliers.
ow disassembled and cleaned, next tap the steel rivet that’s still inside the mounting boss. You could drill it out and tap a much larger retaining bolt but the rivet shank is thick-walled and once tapped accepts a 10 - 32 x 3/8” bolt perfectly. I use a button head allen bolt, flat washer and split washer all in stainless.
efore you start drilling make sure you have the correct drill bit for the tap. In very, very small type on the tap is the drill to use and they go by numbers not size. The 10-32 tap calls for a #21 bit. Drill plenty deep but not too far for obvious reasons. I first do a test tapping on a piece of similar material.
s it worth saving or just buy a whole new gas cap? If the chrome's decent I like to renew the original. It’s certainly much cheaper. Putting on just the seal requires patience to seat it all the way in the groove. A smear of grease helps. If your disc holder and rivet are in good order replace the seal only. In this case, the rivet was rusted badly and had to go. With stainless fasteners this will no longer happen. And you can unscrew it later.
Don’t forget this rubber spacer which goes on the mounting boss followed by the disc with seal.
The button head bolt and washers can be purchased online from a distributor such as albanycountyfasteners.com and are great for other motorcycle applications.
This seal is made of ethanol fuel tolerant “proprietary” polyurethane. Worth a try for $10. Neoprene ones are also available.
Not to scale
Test piece
Tap for #10-32 threads
#21 Tapping Bit
Commando “Ceandess” Fuel Cap Seal Renewal