I have a 1973 Bonneville t140 and my petcock is leaking. The petcocks are new I don't think that rubber on that washer is making a good seal. Can I just use a thread seal? Thanks Don
If you can find a petrol resistant sealer then it should work, i only fit fibre washers and screw them all the way in and then give the lock nut a good turn and never had a problem
Why not try threadseal you never know. You could use wellseal i think , maybe even rtv gasket but as dark says I would try nipping the locknut a little first, or as it is a rubber washer maybe very slightly undoing it , you may have distorted it out of shape.
You need viton seals. I have a T110, and since ethanol was introduced I've had leaks. The cure for me was on eBay LCBspares item no 322262858299 (Lancashire Classic Bikes) Problemo solvo! Taff
You need a Doughty seal. They come in all sizes metric and imperial. The screw thread on the pet cock should be British Standard Pipe Taper (BSPT) so fitting either a Doughty or fibre washer plus giving it a good nip should seal the leak.