Thursday, 24 January 2013

Boiler Fittings (2)

At the end of my last article on attempting to fit the first of the boiler fittings, I'd found that the protruding screws for the boiler fittings were not parallel but pointing out radially from the centre line of the cylindrical boiler.

Faced with the problem of how to make the screws parallel, I took advice from our boiler maker Mendip Steam Restorations.

The important point is to understand how the screws are fitted to the boiler so as not to risk damaging them during the 'parallelising' process. The screws are not engineering studs as I'd thought but high-tensile screws fitted from the inside and sealed using a copper washer. Thus heat should be avoided as it could disturb the seal and any percussive (hammering) approach would not be sensible either.

I was advised that I should use a piece of pipe which would fit over the screw threads so that I could bend the screws cold with the extra leverage. Care to avoid damaging the threads would be needed also.

I settled on the idea of a 1" inside diameter piece of pipe of length 11.25"; this was the maximum length that could be fitted between the boiler and the front of the cab. It would also fit nicely over the 1/2" Whitworth nuts so I thought. Of course plans had to be changed when I found that the screws were 5/8" and the nuts would not fit into the pipe. It's a voyage of discovery with this mistress!

So two larger 5/8" nuts were reduced by angle grinder to fit the pipe as well as the thread. And here they are:
Reduced pair of nuts on the lower left screw
(One nut is close to the boiler shell to avoid bending
the screw near the shell and weakening the seal).
Before attempting the tweak on the front of the boiler where space is restricted, I thought I'd just have a quick go on a more accessible one at the rear (which will eventually support the regulator assembly).

Now I'm not particularly strong but not that weak either but attempting to bend a 5/8" high-tensile Whitworth screw with only 11.25" of leverage was way beyond me (particularly as fine adjustment was needed). So a longer pipe was going to be needed and not a straight one!

And here it is:
A nice fit
And the length?
About 4 feet of leverage
How wide is the cab, I hear you ask? Not wide enough!
New use for the off-side window!
As you can see, the window aperture has found an additional use!

Now I've been able to begin the adjustments but, as luck would have it, a horizontal adjustment is not quite all that is needed. Some vertical adjustment is also needed. So the pipe extension is going to need curtailing.

Nearly there but not quite. At least I now know how to do the parallelising!


  1. How did the screws get so bent out of shape in the first place?

    1. It's not that they were bent out of shape but straight out of shape!
      The boiler is circular. When drilling a hole for a screw, the hole is drilled perpendicular to the surface. If there are two screws a distance apart, they will not be parallel because they are perpendicular to the surface at different points around the circular surface.

      To make them parallel (ish) the screws need to be bent into straightness or "parallelised" as I put it!

      I hope that makes sense? Perhaps I didn't explain it well enough originally.

  2. Hi Andy, following your exploits with interest. Just a thought here: once you've bent the screw, are you going to be able to get the inner nut off (the one down near the base of the screw) ?

    Colin (ex IVC !)

    1. Hi Colin. The screws never need to be bent very much and so the thread is not distorted excessively. The inner nut can be tight to get off but has not been too stubborn so far. We did grind a half-thickness nut later to get over the problem.
      Andy (In IVC since 1977!)


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