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Discussion Starter · #1 · (Edited)
Hi All,

When I took my petcock off on my 81 CM400E to check the screen in the tank last summer, the flat gasket between the petcock and the tank nipple disintegrated into a bunch of pieces. I was able to buy some gasket material from the auto parts store and cobble something together that got me through the rest of the season. Having taken off the petcock again to paint the tank, the gasket is shot again.

It looks like Honda only sold this gasket with the fuel strainer, which of course is not available except from David Silver Spares, and I am not about to pay ~$60 for it. Has anyone found an alternate source of this gasket? I tried finding something that might fit on McMaster but no luck.

I have access to a laser cutter here at work and I was going to buy some flat stock and cut out some appropriate sized gaskets for this. Does anyone have a good condition petcock gasket that they could measure with some calipers? Otherwise I will just measure my petcock(Haha) and guess and check with the sizes. Assuming this works, I should be able to cut out a few dozen of these if people are interested in them/

Thanks!
 

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And this is for your 81 CM400E? I surmised that from your other thread but you didn't specify which bike in this thread.

So you're talking about #9 in this diagram: https://www.partzilla.com/catalog/honda/motorcycle/1981/cm400e-a/fuel-tank

I used a Nitrile rubber o-ring from the harbor freight assortment: https://www.harborfreight.com/397-piece-metric-o-ring-assortment-67580.html
it fits loosely in the petcock collar once you poke it down past the threads. The one I've got in there now is 4 years old. You don't want to use one that's too large, it has to rattle around in there to leave some 'squish' room, oil the two surfaces and the o-ring before tightening, try it dry and it may shred and leak.

I'll see if I can figure out what size I used, I've got another petcock down in the shop somewhere to test fit to.
 

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Discussion Starter · #3 ·
And this is for your 81 CM400E? I surmised that from your other thread but you didn't specify which bike in this thread.

So you're talking about #9 in this diagram: https://www.partzilla.com/catalog/honda/motorcycle/1981/cm400e-a/fuel-tank

I used a Nitrile rubber o-ring from the harbor freight assortment: https://www.harborfreight.com/397-piece-metric-o-ring-assortment-67580.html
it fits loosely in the petcock collar once you poke it down past the threads. The one I've got in there now is 4 years old. You don't want to use one that's too large, it has to rattle around in there to leave some 'squish' room, oil the two surfaces and the o-ring before tightening, try it dry and it may shred and leak.

I'll see if I can figure out what size I used, I've got another petcock down in the shop somewhere to test fit to.
Good catch, added that info to the original post, thanks!

I was hesitant to use an o-ring, I was worried it would try to extrude out since it wasn't contained on the ID. Did you have a problem with the petcock coming loose? I would be worried about over tightening it and damaging the o-ring, but then it coming loose otherwise. If all else fails I might give that a go. Knowing the o-ring size would definitely help, I expect it to be somewhere around a -013 or maybe a -110 if you went with a larger cross section.

Thanks!
 

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I was hesitant to use an o-ring, I was worried it would try to extrude out since it wasn't contained on the ID. Did you have a problem with the petcock coming loose? I would be worried about over tightening it and damaging the o-ring, but then it coming loose otherwise. If all else fails I might give that a go. Knowing the o-ring size would definitely help, I expect it to be somewhere around a -013 or maybe a -110 if you went with a larger cross section.
No worries on over-tightening, that's the reason for using an o-ring that rattles side to side in the bore. When I first tried this I used one that was too large and it leaked each try. Just decide on the angle the outlet points to first, and only tighten the threaded collar until it's tight and the petcock won't turn without significant coaxing, it'll get pretty tight.
I won't be able to get into my shop tonight, snow is expected Wednesday so I'll probably have time then.
Cheers
 

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I got some shop time this afternoon and wanted to post back with the o-ring size I'd suggested previously.

Font Technology Measuring instrument Gauge

Yup, you called it cpl rampage, I used a 110. Any bigger and it would grind up the OD when tightening and leaks would start very quickly. The 110 works very well, but its not really a 110 o-ring in the HF kit.

It shows as 2.4mm width, 9.8mm ID.
I looked it up at https://www.marcorubber.com/o-ring-size-chart-index.htm

And its a little larger than a real 110 o-ring.
The Harbor Freight kit I have contains common metric sizes not USA, British or Japanese sizes.
 

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Discussion Starter · #7 ·
I got some shop time this afternoon and wanted to post back with the o-ring size I'd suggested previously.

View attachment 244978

Yup, you called it cpl rampage, I used a 110. Any bigger and it would grind up the OD when tightening and leaks would start very quickly. The 110 works very well, but its not really a 110 o-ring in the HF kit.

It shows as 2.4mm width, 9.8mm ID.
I looked it up at https://www.marcorubber.com/o-ring-size-chart-index.htm

And its a little larger than a real 110 o-ring.
The Harbor Freight kit I have contains common metric sizes not USA, British or Japanese sizes.
Awesome thanks! I ended up finding a Teflon washer with the right dimensions at work, tightened that down and haven't had any problems. Good to know a regular o-ring will work if I get stuck on the side of the road.
 

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A Teflon washer should work wonderfully and outlast the rest of the bike by decades at least.
 
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