Fixing to loco backhead

[RickyTParticipant @rickyt]

I have been building a 5" gauge Manor to Martin Evans' design for more years than I would like to admit. I have a John Ellis boiler which is some years old and have reached the stage where I have begun work on the various backhead fittings. Some of these (most notably the firebox door assembly and the atomising valve for the sight feed lubricator) need to be fixed to the backhead. My question is how this is best done. I am not aware of any solid stays in convenient positions. I am reluctant to drill into the backhead itself for obvious reasons.

I know that some builders attach these items to a separate plate on the back of the firebox, but that still leaves me with the question as to how the plate itself is then fixed.

I'd be grateful for any advice people may have here.

[RickyTParticipant @rickyt]

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Ricky ,

Conventional practice on models is to bolt firehole door assembly and other major fittings direct to backhead using bronze screws .This basically replicates what was done in full size .

Lots of if’s and but’s in your case though because there are no mounting pads and you don’t know for certain how thick that backhead actually is and if it’s actually adequate to take threads . You may be able to see how thick plate is by looking at bottom of firebox but it’s easy to get misled . Anything less than a definite 3/16 and I’d be wary .

Get it wrong and boiler will be weakened and any test certificate invalidated .

If you do decide to tap threads take it very easy and use new sharp taps and proper tapping grease – removing broken taps from a boiler is not fun .

One individual got round these problems by putting the parts of the firehole door assembly on a steel plate and fixing this to boiler by means of a thin sleeve which closely fitted fire hole in boiler and was clamped on the inside of firebox with little dog clamps .

Back of firebox on GWR engines was lagged with thin steel . Many arrangements can be found but a common one used left and right profiles with joint on C/l . Some others had a one piece top section and bottom in two parts . After a few years in service they were often randomly repaired and patched anyway .

Minor fittings on models can sometimes just be supported by the pipework or bracketed to the lagging sheets .

Regards ,

MikeW

Edited By MICHAEL WILLIAMS on 01/09/2013 16:09:24

Edited By MICHAEL WILLIAMS on 01/09/2013 16:12:14

[Phil AshmanParticipant @philashman88468]

Ricky,

I'm also building a Manor, and have a John Ellis boiler. I fixed my firedoor assembly by tapping directly into the boiler, fixing it with stainless steel screws. I'm not sure if this is correct, or whether I should have used bronze screws as Michael suggests.

The backhead is certainly not as thick as 3/16", nearer to 1/8th I would say, but the fixing seems perfectly sound.

Phil

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi both ,

Many people use stainless steel screws and have no problems but area round firebox is one of the nastiest on the boiler with rapid circulation and a lot of active vapour bubbles .

Combination of active zone , unknown stainless steel screws , funny water and electrolytic effects could cause problems but whether it will or not on any particular engine is anyones guess .

Like all engineering problems you just make the best job of things that circumstances allow .

Taken all round bronze screws are usually a better bet than stainless .

MikeW

[RickyTParticipant @rickyt]

Many thanks for the suggestions.

I was working on the basis (although only a working assumption) it was 1/8" copper as it seems to have been used so liberally elsewhere.

If bronze is indeed the best material to go for, would the screws then need fixing with a solder (comsol?) or adhesive of some description?

[julian atkinsParticipant @julianatkins58923]

hi ricky,

firstly you need to check with your club boiler inspector what is acceptable. i think most boiler inspectors will be ok with a few bolts tapped into the backhead with bronze or non-magnetic stainless bolts. if your club boiler inspector is 'iffy' then use michael's excellent suggestion using the backhead cleading (which you will have to make as it isnt on the drawings). the bolts shouldnt need comsol and if the threads are ok (as they should be) no sealant either.

the atomising valve on the martin evans/fred cottam hydrostatic lubricator is in my view quite unnecessary. i have a simple stop valve on the oil delivery pipe actuated by the regulator quadrant as can be seen in one of my pics in my album. also the martin evans nozzle in the sight glass has far too big a hole in it. No.76 or No.78 will give much better results.

cheers,

julian

[RickyTParticipant @rickyt]

Sounds like bronze screws is the answer then, although I'll only have 1/8" thickness in which to cut the threads. I will run it past the boiler inspector first as he will ultimately call the shots when it really matters.

Many thanks all.

[KWILParticipant @kwil]

Is it possible that you could insert and silver solder into the backhead blind tapped PB bushes. These bushes would need a narrow flange to allow them to be fixed against the back face??

[Phil AshmanParticipant @philashman88468]

That idea occurred to me as well, but I didn't try it because I didn't think I'd be able to get the backhead up to silver soldering temperature. I made up some fixings that consist of a thin hexagon flange, with a threaded piece either side. These screw into the backhead, then the door fitting is fixed to the protruding thread with nuts, the idea being that the door assembly could be removed without having to unscrew anything from the backhead.

The firehole ring protrudes slightly from the backhead about the thickness of the flanges, so the door closes fairly snugly over the firehole.

But in view of what's been said, I think I'll change the fittings to PB instead.

Phil

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