Sealing tapped holes in boiler

On my Emma Victoria build words and music Henry Wood details the firehole door hinges as being secured by No. 6 BA screws drilled and tapped into backhead.

Trying to do a hydrostatic pressure test and struggling to get these screws to seal, already stripped thread so re drilled and tapped for 5 BA. Fasteners put on with some Hylomar red, steel washer and fibre washer.

Is it normal to tap into boiler shell for something like this or would I be better off drilling out and silver soldering blind bushes in.

Bill D.

Hello Bill you should never tap into the boiler shell. Always solder a bush into place and then you can tap to your hearts content.

Regards,

Andrew.

A backing pad fitted at the construction stage would be good, but too late now, but blind bushes are better still, presumably still doable.

IIRC, LBSC used to recommend even tapping handrail stanchions into the boiler barrel

I was a bit dubious when I built the boiler but as this was (and still is) my first loco I thought 'well Henry obviously made it work so will be ok'

I am a bit reluctant to get the blow torch out again but think it's probably best option, if I can't seal it for a pressure test what chance have I got when running in steam.

Bill D.

I was a bit dubious when I built the boiler but as this was (and still is) my first loco I thought 'well Henry obviously made it work so will be ok'

I am a bit reluctant to get the blow torch out again but think it's probably best option, if I can't seal it for a pressure test what chance have I got when running in steam.

Bill D.

Clean with acetone the screws and threaded holes and use high temperature, high strength Loctite. It might be 620, I’d have to check. An example: the cylinder end cap on my Ellie tram’s single oscillator is glued on with this. The register wasn’t even a good fit! No screw threads. The safety valve is set at 60 psi and the tram has run for several hours over several years. Another example: a young fellow’s Maisie had the turret bush strip out. I made a new bush next size up, tapped directly the boiler barrel which was was quite thin, and glued in the new bush. Sealed fine and he got a bit more life out of the clapped out boiler and engine. Obviously not code compliant but it never leaked of came loose.

If you're tempted to use high temp high strength, then make some bronze studs so you don't have to get them out again, in fact that's good practice anyway for something tapped straight into the copper, especially for 5BA tapped into existing 6BA where the thread form is not complete. Once you've got it watertight you don't want to disturb it