Leaky petcock

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Apr 15, 2004
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My left petcock leaks where it screws into the tank. Don't want my bike going up in flames so I want to fix this before riding again. I tried wrapping the threads with teflon plumbing tape but it didn't work. The tape seems to have disintegrated. So I guess I need some sort of thread sealant I can slop on the threads? But what might work and where would I find it? Wondering what other people have done about this...

71 750 Roadster

Sorry to hear of your petcock woes. Are you sure the leak is at the threaded joint? Some of the older fiberglass tanks will develop a leak between the steel threaded insert and the fiberglass bond. Check this out first.

If you're satisfied that you don't have a fiberglass bond problem, try replacing the sealing washer. This washer is steel with a rubber ring vulcanized to it. Also, replace the all-steel thrust washer that becomes sandwiched between the nut on the petcock and the sealing washer. Lastly, make sure that the seal surface on the tank insert is smooth and flat.

You shouldn't need any sealing goop, but a light coat of Yamabond or Gasgacinch applied to the sealing washer will provide some insurance against leakage.



Hi Debby,

I've never seen a fiberglass tank leaking from the threads, but it's a good idea to really check where the leak is coming from. Go ahead for now, try using new sealing washers. The aluminum with neoprene center are the best, but the original fiber washer type also work.

If you have original type petcocks you will need to eventually replace them as the valve area wears out and they leak. The best taps are made by BAP in Germany and were used on late 70s Triumph twins. These are available at most Norton parts outlets. They don't leak!
These are new petcocks and I'm using new fiber washers. The old petcocks had worn out and were leaking through the valve, like a drippy faucet. I bought cheapo petcocks not the nice expensive ones. Perhaps that was a mistake, but the petcocks themselves are not leaking.

Don't know for sure if it's leaking through the threads (hard to tell) or from the insert but the threads in the tank had heavy corrosion and I had to run a tap through to clean them up enough to screw the petcocks in. So I hypothesized that the leakage was through the threads. Guess I should examine a little closer and see if I can confirm that. Maybe I should get the metal/rubber washers too. Do they seal better? Never a simple solution, always complications. Sigh...


The metal/rubber washers RULE !!!

Nortons aren't complicated....they are a learning process.
Some time in the future, you will think you have it all sorted...
Then something else will teach you another lesson :D

Keep Plugging away & you will be almost mistress of your Norton.
Debby, for petcocks I use a washer that looks like it's made of copper. When you see it up close it's a rubber washer enclosed in a thin sheet of copper on three sides. The rubber can be seen inside. They are thick as washers go and are only good for one use. But I like them because they give you the means to tighten and get the right rotational position for using BSA push pull petcocks that have no jam nut. They are made in England I am told. I use a local supplyer who is out right now but some one else may know were to get them.

Hi Debby,

Regarding cheap petcocks from Taiwan, I bought some that look like the original except they use a rubber seal inside the valve. When tightening one of them broke at the threaded portion that goes into the tank threads. Make sure you didn't crack one of your's at this area while tightening the sealing nut.

Another problem with these petcocks is the rubber seal has holes top and bottom that when the valve is open line up with the hole in the valve letting gas through. The holes in the rubber are smaller than the metal and don't allow enough fuel to flow. Worse yet, after moving the tap several times the rubber seal rotates inside the petcock body stopping all fuel flow eventually. Phil Radford from Fair Spares America told me he doesn't supply this type petcock any longer. I do see them on e-bay a lot.

The best replacement are the taps made by BAP.
Looks like the petcocks are ok. I put some Permatex thread sealer on the threads and some Permatex gasket sealer on the fiber washers. I re-installed the petcocks and tightened them down nice and snug. No leaks so far! :)

I just replaced the petcocks on my 75 Commando with a pair purchased on e-bay (without new washers). They leak at the tank and at the bottom where the nipples attaches. Plus after just a few open/close cycles both sides now flow fuel at a very slow rate. I was going to get new sealing washers but it sounds like I got a set of "cheapo" petcocks. They supposedly have brass internals and are good quality. I e-mailed the seller (a brit parts dealer no less!) last week but no response - big surprise... I'll be looking for the BAP petcocks now.
No more cheap chinese petcocks for me! My main petcock plugged up, and now doesn't flow enough to run the engine. Good thing reserve still works - for now. Maybe I should replace both before I get stranded in the middle of nowhere...

illf8ed, If you have "bap's" installed would you do us a favor ? Pull the fuel line and with a tin can underneth turn on the gas. The stream should be smooth with no ripples when you turn them off put a piece of colored paper under the petcock for an hour or so to see if they drip. If they pass both tests write back. If they don't write back. I would just like to know. norbsa
Yes, it is British Parts Chicago. My second second e-mail got a response. They said they would sent me a new pair. They also said they "have sold thousands of these petcocks without any failures. You probably have contamination in your gastank." Sounds like a nolo plea but at this point I'll give them another chance.
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