advice for obsolete leaking fuel line O ring

[garyahouse]

Rebuilding a 1972 Honda CB350 four cylinder. See biccie below. These tubes that connect the carbs below have four O rings.

They are leaking a little. I need a total of 12 O rings or a way to seal the ones I have against leakage.

Typical online sources stock carb rebuild kits, but not these rascals... prolly since they're not really part of the inside of the carbs. What to do? I can't find them anywhere. Honda couldn't even tell me what size they are. O rings are available locally, but they're not rated for sealing gas. I'm thinking of slathering them with a little RTV type product and putting them back in place, but nervous about taking dumb shortcuts here. Need some advice.

Gary

darksider #44

 

[Geezer]

A thin coat of fuel safe RTV would do the job. Don't overdo it.

 

[BkerChuck]

Two suggestions, first have you tried David Silver Spares? He's based out of the UK but has a shop now in the states with good website. He specializes in pre 2001 Hondas.

Second, take one of those to a hydraulic repair shop and have them match it up telling them it's for fuel. I work for a hydraulic shop and my parts guy matches that sort of stuff up all the time. Sealing rings for HD bikes, even the coolant crossover pipe we have to pull on our bikes for a valve check.

 

[RossKean]

New is WAY better than old for this application. Even if you find a suitable gasoline-resistant sealant that seems to hold for a while, the O-rings are still worn, dried out and hardened. Just a matter of time before they break resulting in a deluge of fuel. BkerChuck's suggestion of a hydraulic shop is good. Maybe someplace like NAPA or even a small engine repair shop as well - just make sure that the replacements are suitable for use in contact with gasoline.

 

[garyahouse]

Two suggestions, first have you tried David Silver Spares? He's based out of the UK but has a shop now in the states with good website. He specializes in pre 2001 Hondas.

Second, take one of those to a hydraulic repair shop and have them match it up telling them it's for fuel. I work for a hydraulic shop and my parts guy matches that sort of stuff up all the time. Sealing rings for HD bikes, even the coolant crossover pipe we have to pull on our bikes for a valve check.

Chuck,

Odd you would suggest David Silver. Amazing collection of stuff for the Honda. I couldn't believe it when I saw his website. Wow. However, no O rings for me that I could find. I sent him an email, but no reply expected until Monday.

Also contacted Dime City Cycles here in Florida. They got me the carb rebuild kits in the first place. Same problem though, gotta wait till Monday to hear back from them.

Also, not sure I understand the underlined portion above.

Gary

 

[garyahouse]

A thin coat of fuel safe RTV would do the job. Don't overdo it.

Geezer,

I was thinking the same thing. There's no pressure on these O rings beyond just gravity. Just thought I would see bout some feed back from the forum. Would certainly rather "do it right" if I can, but I'm thinking your option would probably work fine as well. Key is, the bike's for my daughter and you know how dads worry.

Can't do much till Monday anyway.

Gary

 

[dcarver]

It's a long shot.. but what the hell, right?

there is a guy on kz1300.com that sells what looks to be the same exact part.. with o-rings...

 

[escapefjrtist]

McMaster-Carr? I buy all the o-rings for Penske rebuilds through them. Hydraulic shop ^^^^ is a great idea too.

Whatever you do, don't cheap out and try to make something work.

--G

 

[rPGoatBoy]

Measure the o-ring groove diameter and width and buy the appropriate sized Viton o-rings from McMaster-Carr. You may want to buy a few different sizes to figure out which ones work best.

 

[garyahouse]

Goat: That's exactly what I was thinking before I posted this. I've got a set of dial calipers in the garage somewhere. Thanks for the link. Not sure which type of O Ring I'm looking for. From the link you sent me, there's a gazillion sizes. My question is what size? Here's what I'm thinking: I need to find somebody to advise what size O Ring I need once I provide the ID, OD, and width of the existing O Ring slot. Maybe MacMaster Carr can advise???

Escape: I understand about ordering something. I agree. But what I don't know is what size. How much "compression" do I aim for once I know the ID and OD of the "gap" these O rings are supposed to seal?

Ross and Carve: thanks for weighing in here. I'm still debating.

Gary

darksider #44

 

[wetwolf]

jeeezzz, itsa fukin oring. since it's honda, i would venture a guess that its metric. metric orings go by the cross section and the ID or OD.

Heres a chart.

https://www.marcorubber.com/sizingchart-oring-common.htm

looks like about a 1.5x10id to me, you will have to get out a measuring stick. for that application, you can use buna, viton, silicone or epdm, the gas won't kill any of those and if you have a good hydraulic shop around, ask them where they get their orings. If I knew what size it was, I can prolly get them for penies a piece if you buy more than 20 at a time.

15 to 20 % compression work for a pressure situation, you could get by with 5 to 10 Im sure. If the carb bodies have corrosion going on, then go a little tighter.

I would suggest going to some place where there are orings and bring a carb and the fitting and see what fits.

Sorry for the rant, but I'm kinda spoiled here, i have an oring shop half a mile from my work and i get all kinds of orings all the time.

long ****** winter.................................

EDIT--- viton is the most gas resistant, but anything will work for many years without worry.

Da Wolf

 

[BkerChuck]

Gary, by HD I was referring to Harley Davidson. I worked for a dealership for many years. The other comments about metric o-rings are valid points. I failed to catch that the first time I read it.
FJR coolant crossover pipe uses a standard 2-116 n70 Buna o-ring to seal it.

 

[redzgrider]

Here you go:

https://www.justcarbs.com/parts/o-ring_casting_dohc.html

Mike Nixon is the Honda carb guru:

https://www.motorcycleproject.com/index.html

If these aren't what you need, I'm betting a quick email to him would get you the exact specs you need:

[email protected]

 

[escapefjrtist]

<snip> FJR coolant crossover pipe uses a standard 2-116 n70 Buna o-ring to seal it.

@Chuck - Since we're talking o-rings...where did you get the sizing and material?

TIA

--G

 

[BkerChuck]

My parts manager at our hydraulic shop was the first employee here and is an absolute wealth of information. Someone on here at one time listed their measurements from when they did a valve check and I just gave our guy those numbers.I"m at work now and just went back to when I bought them and edited my other post to correct the size. I had posted 2-016 and the correct size is 2-116. When another forum member helped me do a valve check I added several of these to our personal inventory and we used 2 on my bike so I can tell you they are working out fine. I'm not sure what Yamaha charges for them but can tell you that at employee cost I only paid .02 each and we sell them to customers at around .12 each.

I work for a hydraulic cylinder repair shop specializing in large mobile crane cylinders so we buy a LOT of O-rings. We tried matching up fork seals and bushings but they're proprietary enough that we couldn't find a crossover that was worth the risk of being a guinea pig with. We have in the past though matched up several other seals for motorcycles and cars saving our staff lots of money. The O-ring seals that Harley Davidson uses for their drain plugs and charges over $1.00 each I get for about .03 each.

 

[garyahouse]

Finally found the calipers.

From my original picture above:
The existing O ring grooves (in inches) are .098 wide

ID is .239
OD of the bore into which these rascals will be placed is .367

That gives me an .064 per side dimension that the O ring needs to seal.

According to the chart provided by werwolf above, I'm thinking that I should utilize an 071 O ring to create about an 11% compression in the groove.

Looking like a 1.8mm (.071") thickness with a 6mm ID (.236") would just about do it.

Contacted a local hydraulic shop. He recommended Viton O rings. Still looking for a local source.

Gary

 

[BkerChuck]

Gary,

We deal a lot with Parker, a fairly big name in hydraulic seals and o-rings. Based on your measurements I come up with a 2-010 O-ring which I went and pulled so I could measure it. Measuring these things with calipers sucks because it's so easy to expand it with your caliper. Our stock measured at .228 ID x .393 OD. I do not have any this small in Viton but I do have buna 70 which will work for your application. Viton offers better temperature resistance without a doubt but they're not in a terribly high heat application. My cost on these at work is .03 each and I'd be happy to throw some in an envelope and mail them to you. If you can't fine them local let me know.

 

[garyahouse]

Thank you Chuck. You da best. As a matter of fact, thank you to all who've weighed in here. I'm happy to say I know a lot more about this stuff now than I did before.

I do need to confess that I made an error in my numbers above (post 15). I have corrected the wrong number in bold print. I ordered a set of 15 Viton O Rings locally at about noon, but am not sure if they'll work just yet. That order was made before your post above, Chuck.

Oops.

They'll be here tomorrow morning, as my daughter picked them up on her way to work this afternoon. So I should know by later on in the day tomorrow how they fit.

Gary

darksier #44

 

[escapefjrtist]

Thanks for the information Chuck!

My next o-ring order to McMaster will include more parts. Cost of the 2-116 in Buna-N70 is $5.08/100...lots of valve checks there!

--G