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Discussion Starter · #1 · (Edited)
I had very bad fumes so I bought an aftermarket gas cap and then decided to take this one apart which begins by grinding off the edge so the chrome top can be removed. The main gasket is cracked and that probably was causing the smell. The cracking wasn't obvious until I pulled the gasket out:
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Two other rubber pieces are probably equally important with regards to fumes. One is the gasket that resides in the top of the cap. You can see it loosened from its normal position and lying on the upside down chrome top of the cap. Notice how the "C" impressed into the rubber piece (including the small protrusion at the top of it) fits onto the "C" in an assembled cap. IMO into that "C" cavity and with the proper pressure out of the groove in the right of the cap (the small protrusion on the gasket fits snuggly into it) is the only way for fumes and gas to normally escape. Where next? Since the chrome piece is well secured to the body of the cap, I say out the small notch found 180 degrees from the groove.
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I'm thinking it takes a certain amount of pressure for the fumes to get past the rubber piece, raise it if you will. Makes sense, but where is the vent to allow gas to flow out of the tank and into the carbs? I always thought it used the same pathway only in reverse, but just realized that that air probably could not be drawn down into the tank if the rubber piece is snug.
Note the oring on the bottom of the barrel in the picture below. If that failed I assume gas and fumes could get past the barrel and out that way, too:
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A couple more holes:
Finger Material property Nickel Gas Household hardware

The top hole leads into the "C" cavity. The bottom hole is in the wall of what I call the cylinder and it has a brim that is normally not viewable since it is under the gasket. It rides up and down as the cap is closed and opened. The holes probably line up when the cap is closed. The protrusion just below the bottom of the hole fits in the notch in the tank. There is a large spring in the middle of the cylinder. It applies downward pressure on the cylinder which in turn applies downward pressure on the main gasket and forces the gasket against the filler neck of the tank:
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Each of the pieces separated by the spring have an indentation on the other side. The two tangs at the bottom of the barrel fit into them and turning the key makes them lock and unlock. You can see the indentations in the middle of the picture below:
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The rim of the main gasket that sits on the tank is actually pinched between the yellowish ring and the top of the body of the cap. The center of the gasket tore out rather easily. It may not be viewable, but that yellow ring is at a number of points actually pinched onto the body of the cap. EDIT: That ring is easily pried up. Doing so appears to make the task of replacing the gasket possible. Pry up the ring, pull the old gasket out, replace it with a suitable one from an original or aftermarket cap then press the ring back in by hand. Once completed the bad gasket is replaced and in my case I would be able to continue to use the original ignition key on all 10 of the original locks on my Interstate. I damaged this cap but I'm pretty sure there is a way to salvage it.
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Well, I'm still not sure how this thing works. And since I do not think it is in any way repairable none of the above may be of any practical value but I took the pictures and thought someone might find them of interest. BTW, aftermarket caps are readily available.
EDIT: I now think it is repairable, see EDIT above and post #8 below.
 

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Who ever thought a simple gas cap isn't so simple after all? A lot of engineering and manufacturing in that thing!!! Thanks for the pics.
 
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That seal looks more like a ribbed seal than an O-ring on the end of the lock cylinder to me (O-rings, D-rings, X rings &c are so named because of the cross section shape).
If I filled up and then parked so the heat from the engine expanded the fuel the excess used to come out around the lock cylinder of my original cap so I figured that's how they breathed. I never took it far enough apart to find the seal on the end of the cylinder.

And FWIW, I remember a few people saying they had replaced the outer rubber seals on their caps many years ago but all I remember is that I couldn't find one for sale when mine needed replacing.

A fuel cap that sits on top of the tank exposed to the weather needs to have a labyrinthine vent so that rain can't just flow in. I suspect that the original firmness of the rubber seal with the "C" shaped impression and the depth of the groove were designed to allow air in and fumes out well enough and that the space under the steel cover and the hole in the notch on the opposite side (exiting below the rim of the cap) were the labyrinth.
 

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Did the new gas cap stop the gas fumes?
 

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I can't speak for RVP3 but Eccles smelled a lot less after I replaced its cap. And the paint on the tank stopped peeling around the filler all the time too. I credit this to the fuel not being to escape from below the cap (the seal wasn't quite as bad as the one in the first pic in this thread) so it has to expand a bit more before it can exit from the vent.
 

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Discussion Starter · #6 ·
And FWIW, I remember a few people saying they had replaced the outer rubber seals on their caps many years ago but all I remember is that I couldn't find one for sale when mine needed replacing.
I came across a few either suggestions for repairs or actual replacement (don't recall which) and thought that they must be referring to CX500 caps of which I am not familiar. Now that I look at it, though, laying the right size of a suitable material on top of a bad gasket might work. The large spring pushes the gasket down pretty firmly against the filler neck of the tank.
Did the new gas cap stop the gas fumes?
It did. I seldom think of the vents in the fairing but I sure did while riding with the old cap. It went from bad to barely noticeable if at all.
 

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At any rate, the size & shape of the filler (& thus the part of the cap that goes into it) was the same for other Hondas too and replacement caps made for the CMX250C Rebel are relatively inexpensive and plentiful on eBay.

The 250 cap is a bit different shape from the original but I think it looks OK. I even bought a lock set so I could have the same key for the keyswitch and the cap (no steering lock but it fits the space between the bars and the Danmoto instrument panel nicely)
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Discussion Starter · #8 ·
I always thought it strange that the gasket could not replaced because the yellowish ring was pinched in leaving one with no alternative but to buy another cap and deal with another key. The ring actually comes out easily by prying up with a screwdriver using only a little force. In fact it can be pressed back in place by hand. If I had not ground off the edge of my original cap I could have tried to pop the aftermarket gasket out and put it in the original cap.
Aftermarket on the left:

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Appears to me that a gasket could also be used from a known good original cap. Or maybe a NOS one could be found.
 

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Discussion Starter · #10 ·
Yeah, but with all the other rubber bits and years of wear on the moving parts I think I'd rather have a new cap, though...
I hear you, but the originalist in me would sure make me try. :)
 

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Discussion Starter · #11 ·
Keep in mind that for the past 40 years the ignition, side bags, trunk and fairing compartment have all used the same key. Now that's gone. Sad. BTW, the radio uses a different key but I imagine that's the way they came.
 

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That would depend on which model you have. Mine started out as a CX650E so only the keyswitch, fuel cap, the cubby in the tail and the helmet locks. I immediately removed the latter 2 so they don't count. I added an Interstate but the cover over one pocket is screwed down and the other has a stereo mounted in it so no locks there.
I did have a low trunk for a few years (it was pretty simple to make that open with the same key). When I replaced that with a tall trunk I used the same lower lock but couldn't get its upper lock apart to re-key it so I replaced that with a cam lock. I always used the upper one and eventually the lower lock wouldn't open.
I now have a different trunk - with the cam lock.
Along the line I bought the Rebel lock set so I could use its keyswitch and cap (as in the pic above). So I have a total of 2 keys. It would be nice if I could find a lock for the trunk that took the same key but I'm not going to get too upset about it.
 

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Would be nice to keep the orginal key , there are 10 locks on my Silverwing and all the same key. Did you figure a way to get the tumbler out without damageing the cap?
 

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No. I seem to remember someone posting how to take it apart years ago but I didn't bother with the original one because the seal leaked anyway.

For a long time Eccles has only had 3 locks (keyswitch, fuel cap and trunk) and at one point they each had separate keys because they all had different keyways. With the extra wear & tear winter causes things change on it more often than on most bikes so it has been a long, slow evolution to get to what it has now.

I know what you mean about the 10 locks, though. My GoldWing started out as an Interstate with 13 locks keyed the same. The fairing went on the winter machine (with a different lock on the fairing pocket) and I never use helmet locks (anyone with a knife can cut the helmet's strap, not to mention that the helmet will get wet if it rains)(besides, both of my bikes have sidecars to put things in) so that leaves 10 (keyswitch, fuel cap lid, 2 per saddlebag, 2 on the trunk and 2 that attach the trunk to the rack).
Several years ago I replaced the instrument panel and added a speaker box between the new one and the bars and it wouldn't fit with the original keyswitch so I mounted one made for a CT90 in the speaker box. Its keyway was the opposite of the original locks so for a couple of years I needed 2 keys for it (plus one for the topbox that attaches to the sidecar but I only attach that when we travel)(I rarely attach the original trunk unless we are travelling either). Then I decided it would be a good idea to have a spare keyswitch and that one had the same keyway as the bike's original locks so I re-keyed it to match and was back to a single key most of the time.
 

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Swapped rubber gaskets between my Cx and the Gl that sits against the tanks , going for a ride after lunch see if it helps . The Cx rubber looked in better shape .cross fingers
 

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So finally got to test the bike ,no gas fumes ,yeah.
 

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Want to thank RVP3 for posting the pictures and paying the price of two keys. Yes the brass ring prys off with a flat screwdriver so was easy to change seals. Now where to find a low cost new cap to replace the wornout rubber gasket thats on the Cx , at least theres no fairing to trap the fumes in. Thanks RVP3!
 
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Yup, that be cheap enough, thanks
 

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Discussion Starter · #20 ·
Want to thank RVP3 for posting the pictures and paying the price of two keys. Yes the brass ring prys off with a flat screwdriver so was easy to change seals. Now where to find a low cost new cap to replace the wornout rubber gasket thats on the Cx , at least theres no fairing to trap the fumes in. Thanks RVP3!
Your welcome. If you would, let me know if you find a new aftermarket one that has the same dimensions as the original.
 
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