Petcock rebuilding issue

[tkent02]

Just came in like 5 minutes ago from the garage..its now been sitting for around 3 or 4 hrs and still no leakage. I know it needs to fit snuggly against the seat surface of the body. Thats my entire point about the size of the oring in the rebuild kit..its too big to let it slip into the seat properly without binding and its not seating enough to seal completely. I am gonna track down some orings and try them in place of the ones that are in the kit. My gut is telling me this is the issue.

Chuck, there's an O ring oracle in Dallas, somewhere near the old Cowboys stadium. She is a big old fat lady, knows anything and everything about O rings, and she has them all. Every last one... I will try to come up with the name of the company, something like D&E engineering or something with letters like that.

OK, I think this is it:
H&D Distributors,
3236 Irving Blvd.
Dallas, Texas 75247

[sedelen]

Steve, I think not paying enough attention to the o-ring sealing surface is what causes most petcock re-building to fail.

Dale,
I believe with your years of experience this holds true.
I acquired 3 petcocks in addition to the one on the bike, 1 was a GS1000G model so I didn't do much with that. The one on the bike and the other 2 leaked. I had bought a rebuild kit and initially just replaced the diaphram, I eventually put it in all 3 petcocks one at a time, they still continued to leak. It wasn't until I started replacing the 5 hole gasket that they stopped leaking. The same thing happened to GS Rick, he replaced the diaphram on his GS1000G and it still continued to leak, I told him to replace that 5 hole gasket and it quit.
It does state in the GS1000E service manual that fuel in the Prime position flows not via the diaphram but through the reserve pipe. A bad 5 hole gasket could allow the prime to leak. Those things get hard, shrink, and crack, and when they're like that they don't seal very well.
Page 8-2 http://www.mtsac.edu/~cliff/storage/gs/GS1000.pdf


My little petcock testing station. I spent more than one afternoon playing with these petcocks.

[rustybronco]

Steve, In my response, I guess I was assuming to much.

I would hope that most people would be paying attention to all the sealing surfaces and replace parts that are worn or damaged when they overhaul these things. when I overhauled mine, I made absolutely sure all the surfaces the 5 hole gasket seals against were as perfect as they could be, even to the point of polishing the 'lever side's' flat sealing surface with 1000 grit crocus cloth. again, I think, renewing all the sealing surfaces, along with replacing the worn parts, would be what most people normally would pay attention to. where I can see as a failure point in most repairs, is not paying enough attention to the seat the o-ring on the vacuum diaphagm seals against.

[chuck hahn]

Dale..As you guys already know, I am a FIRM believer in the "every part is cleaned like new " approach too. Seeing i took that approach and cleaned every surface and 4 or 5 attempts at installing it still failed and the 750 one sealed first time, thats what made me suspicious of the kit and start comparing the two. I should have right then gotten out the calipers and measured but didnt. The difference was clearly visable though even without my glasses on. I also noticed the new 5 hole gasket was quite a bit thicker than the old and compressed ones. I also tweeked that waffled spring washer thing that goes under the front cover to be sure the lever was being pushed back sufficently to seal against the 5 holer.

[Dave8338]

crocus cloth

One of the few, that even know what that stuff is.

[Roostabunny]

What a relief this thread is! No offense to the guys who advised to buy oem vacuum petcocks when the originals leak, but they also said I wouldn't have to worry about it again for another 26 years! With the price of an OEM petcock for my '81 850G up from $48 to around twice that since I bought a new one about 5 years ago (note - not 26 years ), I decided I had to give the $24 rebuild a try.

So here's my question: How did you guys taper the dowel you used to lap the surface where the o-ring seals. Seems like you'd need it to be pretty exact.

The reason I ask is that I've reassembled it twice, and both times it leaked worse than the original. The first time I realized I hadn't aligned the hole in the inner diaphram with the matching holes on the petcock body and the spacer. But I think that would impact fuel flow, not make it leak. So when it leaked the second time (after also stretching the spring a smidge), I took a close look at the race, and there's definitely a ding/scratch looking thing in there. So what size dowels did you guys use and how did you copy that taper angle?

[rustybronco]

So here's my question: How did you guys taper the dowel you used to lap the surface where the o-ring seals. Seems like you'd need it to be pretty exact.

I took a close look at the race, and there's definitely a ding/scratch looking thing in there. So what size dowels did you guys use and how did you copy that taper angle?

Roostabunny, I just eyeballed the angle on a piece of wooden dowel I had. If you push down fairly hard on the dowel and rotate it on the seat, it will leave a witness mark on the dowel. You should be able to change the angle as necessary from the markings left on the dowel.

[TheCafeKid]

Chuck, before you pass that fuel tap as 100% working, sit the tank out in the sun for a bit and let it get nice and warm and see if she still doesn't leak...

[Roostabunny]

Thanks, Rustybronco!

"Witness mark", I like that. Got the tool carved, but ended up using some polishing rouge from my dremel toolbox. Might be too fine, as the race looked shiny when I was done, but it still leaked. You think valve compound will make a difference?

My neighbor suggested a thin dab of vaseline or dielectric grease to help the seal, but it seems like that'd go away after a few minutes of running. Any thoughts?

[rustybronco]

Thanks, Rustybronco!

"Witness mark", I like that. Got the tool carved, but ended up using some polishing rouge from my dremel toolbox. Might be too fine, as the race looked shiny when I was done, but it still leaked. You think valve compound will make a difference?

My neighbor suggested a thin dab of vaseline or dielectric grease to help the seal, but it seems like that'd go away after a few minutes of running. Any thoughts?

I think Valve lapping compound is what's needed to cut the seat so it comes out round, not a polished oval.

To make the dowel round, chuck it up in a drill motor and sand the angle with a piece of sand paper attached to a flat piece of wood, or if it will fit in a pencil sharpener, that might work as well.

Another thing that might help matters is the size of the o-ring used to seal off the seat. I think the one that comes on the diaphragm in those aftermarket kits might be a wee bit too small. The one I used to replace my old one was a little larger than stock. I used it because it was all that I had on hand, but it sealed perfectly.

[chuck hahn]

Josh..with over just 200 miles and sitting on top of the hot engine for a few hrs..coupled with the 80 degree Texas sun and not a drop...I think its gonna be ok,,,for how long is of course anyones guess.

[Roostabunny]

Josh..with over just 200 miles and sitting on top of the hot engine for a few hrs..coupled with the 80 degree Texas sun and not a drop...I think its gonna be ok,,,for how long is of course anyones guess.

Ha, Chuck, thought you were talking to me. Until I remembered that TheCafeKid is a Josh, too.

Out of curiosity - do you know the dims of the o-ring that worked?

[chuck hahn]

Nope...not gonna take it apart.

[Roostabunny]

To make the dowel round, chuck it up in a drill motor and sand the angle with a piece of sand paper attached to a flat piece of wood, or if it will fit in a pencil sharpener, that might work as well.

Another thing that might help matters is the size of the o-ring used to seal off the seat. I think the one that comes on the diaphragm in those aftermarket kits might be a wee bit too small. The one I used to replace my old one was a little larger than stock. I used it because it was all that I had on hand, but it sealed perfectly.

Cool deal, thanks, RustyBronco! I picked up some lapping compound and a 3/8" hardwood dowel. I think the pencil sharpener (which did fit the 3/8" dowel) was a good way to get started, but I'm fairly certain the angle is too shallow compared to the seat. But the drill is a great thought to finish it up and keep it round, thanks!

Meanwhile - same question for you as I asked Chuck: Do you happen to know the size of the o-ring that worked for you? No guarantee that'll be the right size for mine, I guess, but it's a starting point to try.

[Roostabunny]

Nope...not gonna take it apart.

Of course not. I was just crossing my fingers that you knew what it was when it went in.

Edit: Because when I'm trying to solve a gas leak with a part that doesn't work right I always take measurements as I go.