Smokebox to Boiler joint

Please can I call on you all again for some assistance, I am trying to fit a smokebox to a boiler, the front of the boiler is out of round, as you would expect it to be, by about 15 thou. I am boring the smokebox rear ring to fit the high spots but I will be left with gaps which I assume need to be sealed. I have read lots of construction articles by Evans, Young and LBSC and none cover the fitting and sealing, Jack Buckler in the Sweet Pea book says to bore it a relatively easy fit on the front of the boiler barrel, not a word about any subsequent sealing. How do you all do yours?

15 thou out of round at the smokebox is what I would call very accurate. It is not a pressure joint and can easily be sealed with heat resistant gasket sealant, graphite type or similar. Full size riveted seam boilers had gaps bigger than this and were sealed by peening the plates with a chisel to seal the gap. These had to seal against the full boiler pressure.

Paul.

Hello Baz,

I wouldn't worry about the 15 thou gap when fitting the smokebox to the boiler; if you intend fixing the smokebox to the barrel, e.g. bolting it or fitting a few screws then most of any gap will disappear. I'd recommend a smear of gasket sealant, Heldtite or similar to both surfaces prior to assembly and that'll do the trick. Some folks will also put a bead of silicon sealant around the joint at the rear of the smokebox as an additional seal, but with only .015" gap I think it is a bit superfluous.

I've used the foregoing method for many years with complete success.

Regards,

Bob

Thank you Paul and Bob for your replies, I have located a stockist of Heldtite so I will be purchasing some this week.

hi Baz,

silicon sealant if perfectly ok. it will fill a 15 thou gap. car gasket sealant is also ok. you can always tap the copper to get it to fit. it wont do the boiler any harm.

dont ever use fire cement as advocated by Mark P. it will crack and leak. i always make mechanically sound joints around pipes in the smokebox.

cheers,

julian

Julian,

Silicon sealant as in the stuff the local DIY shop sells for sealing the bath etc? I was not sure if it would take the heat but if you recommend it I am sure there is half a tube of it in the shed, left over from domestic duties.

Thanks

Barry

hi barry,

yes ordinary silicon sealant is perfectly ok. however there is a high temp version available from Screwfix for sealing fireplaces.

cheers,

julian

If there's 'half a tube' of silicon sealant anywhere on the planet, I've never found it

Neil

Car accessory stores sell high temperature silicon gasket material for use on car engines.

Old thread, but I will prolong it. I want to add dummy rivets around the smokebox joint of a 5" SPEEDY. Do I drill for the rivet, lightly countersink inside and set the rivet, or use soft solder and then clean up afterwards or use some sort of glue ?
BobH

Why not screw it on with slotless roundheads, look like rivits but don't need hammering home.

When I have done dummy rivits I just deburred the back of the hole, cut rivit so length equals metal thickness and then one punch mark in the rivit has been enough to expand it in the hole. Taper reamer can also be used from the inside rather than a csk