Tuesday, 23 December 2014

Keeping the Heat In (A Cover-Up!) (1)

From the beginning, Sentinel 7109's boiler had a top cover as shown in this old photo below:
Inside cab (a long time ago)
(Photographer unknown. If you claim to own this photo, please leave me a comment).
The cover was part of the miscellaneous collection of items belonging to but not fitted to 7109 on arrival at Midsomer Norton in 2004.

It has lain largely untouched for the last ten years but its turn has finally arrived. Looking at its original condition, it's not difficult to imagine why I'd ignored it until now.
Original condition showing the rusty edges
It doesn't look much better in the old photo at the top.
Close up of top/side join
The cover was made with top and side panels riveted to a curved angle iron support piece. As a guess, I would say that the riveting prevented any rust-proofing from getting between the angle iron and top or side panels. Thus continued exposure to condensation and wet caused rust to form and squeeze apart the joints. The result was a 'corrugated' appearance and many sharp edges. I could not see how this could be simply 'tarted up' without complete disassembly.
No better from the inside
I ground off all the 150 or so rivets for the various joints and punched them out. (The idea of removing 150 rivets was the main reason why I had kept well away from this task before! I even had to replace my long-serving angle grinder after it started to issue metal gear fragments and smell of hot plastic!). Eventually I was then able to practise my panel beating technique to flatten the areas to be re-joined.
Half top cover after deconstruction
The temporary joins look a lot worse than they really are. They will be screwed together with dome-head screws which bear a resemblance to rounded rivet heads.
Close up, better than it was
Now, after a coat of red oxide paint, one of the top covers is starting to look presentable.
After a coat of red oxide primer
Potentially, the cover could get very hot as it sits on top of the firebox and superheater which at times can glow red with heat. Much of the space will need to be filled with ceramic wool wadding to keep the heat in.

Also worth noting is some detail in the old photo at the top of the article. The superheater tubes coming out from the top of the boiler to the regulator and stop valve assembly are lagged. I think we had better do that too (could be a little hot to the touch otherwise!).

Tuesday, 2 December 2014

Leaky Axle Box Gasket

Each of Sentinel 7109's axle boxes supports its corner of the loco on a plain bearing and has an oil bath in the bottom. A large sprung pad sits in the oil bath and is spring loaded against the lower surface of the axle bearing. The pad acts as a wick to lift the oil to the lower bearing surface. As the axle rotates, oil is carried round from the pad to the weight carrying upper surface.

Some time ago, I'd noticed that one of the axle boxes seemed to be retaining its oil level much better than the other three.

I checked whether there was any water under the oil in the offending box using an oversized horse-syringe (for want of a better name).
One of these
There was a lot of water!

On removing the covers from the two right hand side axle boxes, the oil retaining one showed signs that its gasket was split at the top. On further inspection, both the right hand side gaskets were in poor condition and weren't helped by being disturbed.

New gaskets were made for both of them. (As no problem has been apparent with the LHS boxes, they have been left alone).
Front RHS gasket of 1.5mm Rubberised Cork
With the cover on, the axle boxes look like this.
Assembled (complete with missing stud!)
The missing stud will be replaced, of course (and the wheels will be painted).

Note: These photos have been cropped. If there are any modellers wishing to copy the axle box detail, leave me a comment below. I have other photos with more detail that I can supply on request.

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