For petcocks with a tapered barrel, I’ve used polishing compound to remove burrs and get them to fit better. Be sure to go all the way around when turning the barrel in the fitting. If the petcock has a spring to hold tension, stretching the spring a bit might help. Where a threaded nut is used (Caille, for one) a little of the yellow thread tape mentioned in the previous post can be used to replace or supplement the original gasket in the gland nut.
For compression fittings, remember that the threads on the fitting and the compression nut are not where the seal is made, so adding sealant there won’t help a leaking compression fitting. The seal is made when the ferrule digs into the tubing, then is deformed in the taper of the fitting itself. The threaded nut just holds everything tight. The ferrule needs to be straight on the tubing, and once set, probably won’t work in a different fitting. Compression nuts which are split need to be replaced. A tubing bender will do wonders keeping the tubing from linking when you make a new one.
The compression fittings on the late ’20s Evinrude twins with pressure / vacuum cooling have non-standard threads. These are often messed up on these Fleetins, Fastwins, and Speeditwins. Don’t try to force a standard nut on these fittings.
Tom
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