Steam dome

[Boiler BriParticipant @boilerbri]

The rebuild of a 5" Brittania that I have bought was going well until I pressure tested the boiler. A couple of small leaks need dealing with so the boiler has been stripped in order to prepare it for the repair.

The dome plate was held in place with ten high tensile cap head 6ba bolts. These were rusty which made it hard to get the Allen key in. They had gone rusty because the tapped hole in the centre of the plate that holds the cover on was tapped right through into the steam space. When the cover was screwed down there was no way to seal the thread, unless a bit of thread sealant was used on a wing and a prayer. I will silver solder a blind bush on the cover plate base so that the steam can not leak and the cover screw will go into a blind hole.

With the tapped ring being bronze that the cap heads go into do I need to replace the cap heads or can I use brass screws? The brass is not in contact with the steam or boiler water, so no dezinkification will take place.

Your advise everyone please.

Bri

[Boiler BriParticipant @boilerbri]

[julian atkinsParticipant @julianatkins58923]

Make up proper fitted stainless bolts out of stainless hex.

Do not use brass screws, due to lack of strength.

Cheers,

Julian

Edited By julian atkins on 24/04/2016 21:58:30

[duncan webster 1Participant @duncanwebster1]

whilst I agree that SS hex head bolts are the best bet, as they are in tension they don't need to be fitted. If you can find 6ba SS bolts to buy they would be OK. Ebay list them (actually hex head screws, but now I'm being pedantic)

Edited By duncan webster on 25/04/2016 00:09:02

[julian atkinsParticipant @julianatkins58923]

This is a bit of an aside but partly links into Duncan's post above.

The most common leak on the inner dome IMHO experience is around the bolt head rather than the flange. I have a view that this is due to the greatly reduced flange mating surface where the bolts are located, which in 'scale' miniature locos is always rather less than optimum.

Fitted bolts with a plain unthreaded length to match the inner dome flange reduce this problem considerably.

I only ever use stainless on boiler fittings for bolts etc.

They are a pain to make, but well worth the extra effort.

Cheers,

Julian

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