Sealing a thread between ally and brass.

[Dave Plowman (News)]

There's a steel heater pipe which runs under the inlet manifold on my old
Rover. And being steel it naturally rots away with time. It's also NLA.
I made up a new one out of ordinary 15mm copper tube sweated into a 3/4"
male conduit bush which has the same TPI, but maybe not the same actual
thread. But it does screw in all the way and tighten securely. However,
despite loads of PTFE tape, it started dripping slightly after a few
years. What would be the best thing to seal it with? The manifold is
ally - the bush brass. And requires a major stripdown to get at.

 

[The Natural Philosopher]

There's a steel heater pipe which runs under the inlet manifold on my old
Rover. And being steel it naturally rots away with time. It's also NLA.
I made up a new one out of ordinary 15mm copper tube sweated into a 3/4"
male conduit bush which has the same TPI, but maybe not the same actual
thread. But it does screw in all the way and tighten securely. However,
despite loads of PTFE tape, it started dripping slightly after a few
years. What would be the best thing to seal it with? The manifold is
ally - the bush brass. And requires a major stripdown to get at.

some sort of Loctite or red haematite type gunk maybe?

 

[Andy Dingley]

despite loads of PTFE tape, it started  dripping  slightly after a few
years. What would be the best thing to seal it with?

Liquid PTFE. Fiver a bottle or so, Screwfix et al.

 

[F Murtz]

There's a steel heater pipe which runs under the inlet manifold on my old
Rover. And being steel it naturally rots away with time. It's also NLA.
I made up a new one out of ordinary 15mm copper tube sweated into a 3/4"
male conduit bush which has the same TPI, but maybe not the same actual
thread. But it does screw in all the way and tighten securely. However,
despite loads of PTFE tape, it started dripping slightly after a few
years. What would be the best thing to seal it with? The manifold is
ally - the bush brass. And requires a major stripdown to get at.

glycerine and litharge, if you can still get litharge

 

[Cicero]

There's a steel heater pipe which runs under the inlet manifold on my
old Rover. And being steel it naturally rots away with time. It's also
NLA. I made up a new one out of ordinary 15mm copper tube sweated into a
3/4" male conduit bush which has the same TPI, but maybe not the same
actual thread. But it does screw in all the way and tighten securely.
However, despite loads of PTFE tape, it started dripping slightly
after a few years. What would be the best thing to seal it with? The
manifold is ally - the bush brass. And requires a major stripdown to get
at.

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Plumbers' hemp and Boss White; work the Boss white into the strands of
hemp before winding it into the threads. If it's close to a lot of heat
you could use asbestos string instead of the hemp.

Cic.