Topic: All my petcocks leak. I'm up to seven now. I've switched parts

[Mavryk03]

That's the explanation I was looking for. The gas leaks by the fiber washers into the fuel delivery area and then out the brass delivery tubes - really,.. really? OK so I'll get out the allen stainless bolts and the breaker bar and have at it tomorrow with some new copper washers. I guess these old arthritic hands aren't what they used to be.

And no, it wasn't leaking from outside or around the petcock. It was coming out of the bloody tubes - as if I hadn't shut the gas off!! And I do have a pesky float valve on #1 that does want to dump gas on the floor occasionally when the bowl fills from a leaky petcock!!

Mine is the same way but # 4 instead of # 1, I will have to try some of these methods

[mycb750k6]

So yesterday I went to the hardware store because they have a huge selection of metric O-rings in all imaginable sizes. I was going to try the O-ring under the screw head trick from earlier in this thread. A friendly salesman asked if I'd found every thing I need and I told him what I was doing. He said Oh no, you can't do that. Gasoline dissolves rubber. He said in fact all petroleum products do. So I felt like an idiot, put everything back and went home empty handed and then thought my engine is full of O-rings that come in contact with oil all the time. So is there any truth to the statement that gasoline dissolves rubber O-rings? I'm a little annoyed at myself for taking what he said at face value now.

[Bob Wessner]

It does have to be specifically formulated for contact with petroleum products or vapors. Not all rubber is. For instance, nitrile is formulated for this purpose.

[mycb750k6]

OK, well he did say try an automotive parts place so that's what I'll try next and see if they have anything that size and material.

As an aside, I bought a few O-rings from the H/W store to use in my head under the rockers and again around the cylinder studs because I lost the ones in my gasket kit. I guess I've got a ticking time bomb 

[IndyFour]

I had the same leaking issue with my 550 petcock....it mounts in the same fashion as yours does with the two screws inside the sediment bowl sealed with two fiber washers.

Not being able to find new fiber washers locally (i've since found them), I ended up researching what different materials were "gas proof".  As it turns out, nylon is fuel safe and so I went out and found some nylon washers at Lowes.  They are slightly thicker than the original fiber washers and do compress a little bit.  They've been in there several months with no leaks so far.  Cheap too.

I had also considered using copper washers (two or three stacked on each screw)....that was going to be my backup if the nylon didn't work.

[eideteker]

Mine wasn't leaking without teh washers, but that didn't last long.  I used Gylon gasket material from work (after letting a small piece soak to check for problems, couldn't find anything online that said Gylon was or wasn't approved for fuel-contact application).  Also replaced those wonky, half-stripped crosshead screws with hex cap screws - been almost a week now, holding fuel so far. 

[mycb750k6]

OK so I finally put the allen button head bolts in along with the stock fiber washers and cranked on them until they squeaked and I couldn't turn them anymore. No more leak. Glad that's fixed. Whew

[Mavryk03]

OK so I finally put the allen button head bolts in along with the shock fiber washers and cranked on them until they squeaked and I couldn't turn them anymore. No more leak. Glad that's fixed. Whew

hey can you put a pic up of what you did so i can see i need to do that to mine as well thanks

[mystic_1]

Glad you got it sorted!

BTW CB750 petcocks can go for up to $50 on eBay, so those six spare ones should fetch you a fair bit of scratch

mystic_1

[jyck]

Has anyone tried using some kind of gasoline safe teflon tape?  I'm struggling with the same issue.  The nylon washers slowed the leak but there's still gas on the floor.

[mycb750k6]

Mystic, you're right. Now that I know there's nothing wrong with them, I'll probably sell a few. I dislike ebay however and will maybe try to sell some here. Although whenever I sell something, I almost immediately need it again.