Filler cap gasket

[Bill2001]

The rubber filler cap gasket on doesn't like to stay stuck to the inside of the filler cap. Looks like it was affixed with epoxy at one time (which I figure won't stay glued to rubber or plastic with gasoline sloshing around). What adhesive should I use to fasten the gasket to the cap? It seems that a newer gasket might not have shrunk and would "snap in" to the cap better, but at $15/per, I thought I'd ask first. (Wombat 94)

--Bill

[socalhodaka]

You could take a chance on eBay, or another used one, if you glue it into the cap you might plug the very small but important vent hole. $15 is a bargain, some people look at these old bike and the old ads like a piston for $10 and try to relate that to today
. These old bikes are not cheap, but a lot of fun.

[Bill2001]

The replacement gasket is $15 and the replacement cap with gasket is only $33 which isn't too bad. I have another good cap, less gasket, on my "pristine tank" (no dents or dings) so I may take a chance on a new gasket. The current cap+gasket works and doesn't leak, the gasket disc is not adhered to the cap and it takes some fiddling to get the cap and gasket on. I was wondering how the rubber gasket was fastened to the cap from the factory. It would be hard to find a gasoline-proof adhesive.

Yep, that vent is critical.

--Bill

[Dale]

Bill,
I don't believe that the gaskets were ever adhered to the caps. When new, the gaskets fit snug enough inside the cap that they stay together as one unit. As they get older the rubber tends to shrink a bit and want to fall out. If it does not leak then I guess it is just a matter of inconvenience. If bad enough, thankfully, new ones are available.
Dale

[Bullfrog]

Dale's comments accurately describe the situation.

Ed

[rlkarren]

I have an idea that I've been wanting to try...

I was rebuilding a carb one time and forgot to remove the rubber o-ring when I put the carb in the chemical soak. 3 days later and the o-ring was almost twice the original size. I noticed after a few more days that it didn't return to its original size so that's when I had the idea to put my own gas cap gasket in there since it also does not stay in.

I haven't done it yet but I am planning on it. I don't know how long to leave it in but I suppose an hour or so might do it.

$0.02

Roger

[taber hodaka]

Yea but don't leave it i longer than three hours, twelve minutes and 19 seconds. just kidding, let us know the results. -------Clarence

[admin]

The new reproduction rubber gas caps are made from viton rubber. Very expensive and fuel/oil resistant. Easily can make new gaskets out of plain material for a lot less but they will not last.

[Bill2001]

That makes sense-- as an elastic ages it can shrink and a good way to hold it into a screw-in cap is to have a snuggish interference fit. The Teutonic BMW would (and does) overengineer a simple gas cap, but the UJM has a simpler solution that last only a couple of decades. I'll get a replacement gasket next parts order.

Yep, chemical carb cleaners can wreak havoc on anything organic. The dip-basket cleaner was much stronger than the EPA-mandated stuff we get nowadays. But necessary on carbs that have had fuel and lubricating oil evaporate to dryness and water corrode the potmetal in carbs.

Paul-- the gasket is in "good shape" but you can tell it is old. Viton is a good material. And the price is not that bad-- the BMW's are thin cork in a two-piece formed housing and the chromed potmetal caps have been NLA for decades. I'm just glad to be able to get parts without a lot of angst...

--Bill

[---]

Rubber or synthetics swollen but carb dunk are permanently compromised. They do more than simply swell, they also decompose or at least lose much of their original resilience. You can try it but I don't think it will do what you think it will. I would rather glue it in with fuel resistant adhesive.

[bchappy]

Keep in mind that the tank rim seals in the very outer edge of the cap gasket, so if it has shrunk very much it may not seal. Of the 3 Hodakas I have restored none of the gaskets would stay in so I replaced all 3. They fit tight and I have not had to worry about them leaking.

[Bill2001]

Absolutely correct-- the old gasket is about 1/8" smaller than the new one I got today. The new gasket pops into the cap and fits snuggly. Should work like a charm.

Being a packrat, I'll hang on to the old cap gasket "just in case"...

--Bill

[viclioce]

My Road Toad didn't have one in the cap. I just ordered a replacement. Got it yesterday. I was looking at caps on eBay and the prices there are even becoming rediculous! Someone was asking $34.95 for a used cap!!! Don't even know if it had the gasket in it. ; o Victor