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Author Topic: Gas cap help  (Read 1291 times)
Spurlock
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« on: January 03, 2018, 05:32:38 PM »

My bike has apparently been fitted with the domestic Japanese style gas cap, and whoever ground off the protrusion on the front edge (to make it fit the USA tank) got sloppy and nicked the sealing rubber, allowing gas to leak into the well under the cap and down the drain hose. So I'm looking at solutions.



I'd rather stick with a stock cap rather than swapping for an aftermarket keyless one, but I know that is an option. Other options are to buy a new cap, still available from Honda apparently but expensive plus I would rather have just one key for everything.

Another option might be to buy a used cap and try to either swap the key cylinder or swap the good seal onto mine. Has anyone successfully done either of these things? I saw a thread from several years back where morti said he had changed locks. I assume that changing either the lock or the rubber requires bending back the punched areas around the outer rim as shown below. Has anyone done that?

My first thought was to look for some magic flexible fuel-proof sealant to fill the grind marks in the gasket, but so far I've come up empty there. Any help would be appreciated.



-Bill
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1975 Honda CB125S2, 1989 Honda NX250, 1989 Honda GB500, 1989 Honda CB-1
Spurlock
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« Reply #1 on: January 03, 2018, 06:48:59 PM »

I think I found a solution. Managed to get the old gas cap apart and now see how the rubber seal comes out. So I've ordered a $13 Chinese knock-off CBR cap and will take it apart and use its seal in my cap. Here's how the disassembly went:

I had an old screwdriver with the end formed into a slight hook. I used it to lightly tap outwards around the rim of the casting to bent back the punched areas that were holding in the steel ring.



I then put the screwdriver in the slot of the ring and twisted lightly. The corners of the blade are ground sharp and square so by twisting it grabbed the steel ring and i could pull up with good force. I probably did not need to do the outward tapping of the punched areas since twisting the screwdriver pushed the casting away. I kept moving around the ring, twisting and lifting and the ring began to raise up. In a minute or two it was free.



Then I saw that it is the steel ring that holds the rubber seal in place. Lifting off the rubber and a washer below it, this is what I saw:



Removing the three screws exposes the lock, and I suspect that at this point inserting the key and turning to the unlock position would let me pull out the lock. But a little voice told me that might involve springs and small parts flying around, so I think I will take the safe option and just swap the rubber sealing ring from the new cap, assuming it looks good..



-Bill

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1975 Honda CB125S2, 1989 Honda NX250, 1989 Honda GB500, 1989 Honda CB-1
a_morti
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« Reply #2 on: January 04, 2018, 04:06:04 AM »

Good work, useful pics!

It was a lot of years ago I had a cap apart after my bike was stolen and recovered. Can't really remember how that went, but I got the cap off some other honda and had to swap some stuff between one and the other. Must have been ten years ago now, amazing how the web holds stuff for posterity.
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Spurlock
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« Reply #3 on: January 04, 2018, 09:47:37 AM »

Good work, useful pics!

It was a lot of years ago I had a cap apart after my bike was stolen and recovered. Can't really remember how that went, but I got the cap off some other honda and had to swap some stuff between one and the other. Must have been ten years ago now, amazing how the web holds stuff for posterity.

Thanks morti, it was your earlier posts that encouraged me to dig into the cap. Now I have to hope the Chinese gasket is decent quality and fit. Many Honda models used that same gasket even with very different cap designs, so if the Chinese part looks dodgy I can always look for the lowest price Honda cap and cannibalize it.

-Bill
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« Reply #4 on: January 04, 2018, 10:31:28 AM »

If you have a local breaker it would be a good way to find that. Maybe they would have a cap with no key or one which has been screwdriver'ed.
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« Reply #5 on: January 06, 2018, 05:59:08 AM »

Hi Bill, good to find you on this forum site. If you read my RVF400 rebuild on BARF you'll see I went thru a gascap teardown. To get at the gasket you need not unbend the casting punches. In fact, I found them extremely brittle and broke a couple on the China knockoff that I tested on. Instead I used a flat bladed screwdriver to work under and around the rubber seal to "pry" out a metal washer (kinda like putting a tire bead onto a wheel rim) that is held in by the gasket. Once this large washer ring is removed there will be 3 screws buried under the gasket securing the rubber to the cap. Pell the rubber back and unscrew the 3 Phillips screws.

The China caps are of very decent quality esp for the price. I got a helmet lock, gas cap and ignition for $15! Shipped!

Following your work and inspired to make a few changes. Thanks!
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Spurlock
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« Reply #6 on: January 06, 2018, 10:36:41 AM »

Hi Bill, good to find you on this forum site. If you read my RVF400 rebuild on BARF you'll see I went thru a gascap teardown. To get at the gasket you need not unbend the casting punches. In fact, I found them extremely brittle and broke a couple on the China knockoff that I tested on. Instead I used a flat bladed screwdriver to work under and around the rubber seal to "pry" out a metal washer (kinda like putting a tire bead onto a wheel rim) that is held in by the gasket. Once this large washer ring is removed there will be 3 screws buried under the gasket securing the rubber to the cap. Pell the rubber back and unscrew the 3 Phillips screws.

The China caps are of very decent quality esp for the price. I got a helmet lock, gas cap and ignition for $15! Shipped!

Following your work and inspired to make a few changes. Thanks!

Hi Rick, Maybe your VFR cap is different, but on the CB-1 and other CBR caps the rubber seal is clamped in place by the outer ring with the "V" shaped profile. The cap seal flares out at the bottom and is pinched in place by the ring. The 3 screws only hold the latch/vent assembly and its separate gasket in place.



You're right about the casting being brittle, and when I get my Chinese part I will just work the flat blade screwdriver with a twisting motion in the groove of the ring, to spread it and at the same time gently push the casting punches out. Much safer than tapping directly on the casting. I'll post photos back here when I have the part.

-Bill
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Spurlock
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« Reply #7 on: January 09, 2018, 09:09:58 PM »

OK, I received the Chinese clone CBR gas cap today and it looked like an exact copy and well made. One option I was considering was to install this aftermarket cap but swap in my lock so it would open with my existing ignition key. But after screwing it onto the tank and closing the cap, it sat slightly ajar as if not pushed all the way closed. So I went with my original plan which was swapping the Chinese cap seal into my Honda cap. Here's how it went:

The existing domestic Japanese CB-1 Type 2 cap, left, and Chinese aftermarket right.



To remove the compression ring that holds the rubber seal in place, I started by carefully prying in the V-groove of the ring at each spot where the cap casting was swaged, in order to spread the swaging a bit.



Then using the modified screwdriver with the tip bent into a slight hook as shown in a post above, I twisted and pulled to lift the steel compression ring out of the cap. Here you can see the ring is lifting out of the casting.



After doing the same on the existing cap, here are both caps with rings and seals removed.



The Chinese seal looked identical to the OEM, so after placing it in my cap I needed to press the steel compression ring down tight against the seal before swaging the ring in place. A 2" PVC coupling turned out to be the perfect diameter to press the ring tight against the seal using a woodworker's vise.



Then with the ring held tight against the seal rubber I went around the circumference with a hammer and punch to swage the ring in place.



Voila, a new seal installed in my old cap. Now to see how the Chinese seal material holds up over time.....



-Bill

« Last Edit: January 09, 2018, 09:12:30 PM by Spurlock » Logged

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« Reply #8 on: January 10, 2018, 08:24:45 AM »

Thanks for posting this, very useful.

It's a shame it sat proud because they both look identical. Did you work out why it didn't close properly?

I have a problem with my gas cap too, the mechanism is well corroded. I frequently lubricate it and it's fine for a while, then it gets stiff again. One day I'm going to snap my key in the lock. I could do with replacing it really, but because you've taken yours apart do you have any idea how easy it would be for me to take the latching mechanism apart to give it a proper clean up?
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Spurlock
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« Reply #9 on: January 10, 2018, 12:32:32 PM »

Thanks filterMan,

I didn't bother figuring out why the Chinese cap sat proud when closed, probably should have. I suspect some small dimensional difference in the latch pieces or the hinge location.

Taking the latch and lock mechanism apart is actually not too hard. You should be able to pull those parts out without removing the sealing ring/gasket although I suspect it would be easier with the sealing ring out of the way. Plus you risk tearing the seal by leaving it in place. There is a steel washer under the lip of the seal, pictured in the photos above. The washer has a notch to clear one of the latch pawls. If you have not removed the seal, lift the seal lip and rotate the washer to align the notch, then lift the washer with a small hook and tease it out from under the seal (hopefully without tearing it!) Then 3 screws are exposed. Remove the screws and the lock and latch mechanism will lift out. Note which way the key tumbler is oriented. Insert the key into the lock and pinch the latch pawls slightly together while pulling lightly on the key. Make sure the key slot is facing down, otherwise the small brass colored plates shown below can fall out the other side. Here is the tumbler part way out.



And here it is all the way out. The brass colored plates are T shaped, so with the wide ends facing up as shown in this photo they cannot  fall out the opposite side. Each is a different length corresponding to the notches in the key, so if they were to fall out you would have to find their correct locations by trial and error or studying the key notches. Best not to let them fall out!



Hope this helps,

-Bill
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« Reply #10 on: January 10, 2018, 03:14:03 PM »

Thanks for that, I'll be taking it all apart at the weekend, it's good to get photos of it all.

Cheers
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