Monday, 19 January 2015

Extending the Chimney Bases Upwards

After fitting Sentinel 7109's new chimney bases, Sunday 18th January 2015 was a busy day spent attaching the four chimney tubes.

Having assembled both chimney units completely in my garage before bringing them to site, I was confident that things should go together without mishap. (Odd how it's the one thing you didn't check that comes back to bite you!).

The tubes are numbered from One to Four as Left Front, Left Rear, Right Rear to Right Front. Each tube had been labelled with the corresponding number of Centre Pop 'pips' (really useful if you can find them again!)
Number One Tube in place
Numbers One & Two
Numbers One, Two & Three
Numbers One to Four all in place
All fitted and seeming to be going well.
View from Above
The photo below gives an impression of how the cab will look eventually.
Exhaust Steam Pipe to Numbers Three & Four Tubes
Finally, here's the first heat shield in place and this is where things began to bite back.
First Heat Shield around numbers One & Two Tubes
The one thing I hadn't checked in my garage was how the two chimney pairs looked together. Looking closely at the photo above, the heat shield on the left seems to converge towards the tubes on the right. At first I thought it was a camera lens effect but the truth was revealed when I attempted to fit the second heat shield on the right.

The left and right hand pairs of tubes converged so much that the second shield could not be fitted using the standard mounting method.

After removing the heat shield again, the measured gap between the tubes at their lower end was 5" but only 4.25" at their upper end. Clearly this would not be acceptable (and definitely not a problem that would be encountered on a single engined Sentinel loco!).

In many of the above photos, I've endeavoured to ensure that the vertical strap behind the chimneys holding the two halves of the cab front together is dead upright. As the photos progress, the leaning inwards of the left hand chimney tubes begins to be more obvious.

Now it's going to be a bit of a grind to make the LH tubes upright and parallel to the right hand ones.

Oddly, by rotating tube number two 180 degrees, the leaning is less so it would appear that the part of the tube which fits over the base casting is not quite in line with the tube's axis. However, that is not much help as the mounting holes don't align with it that way round, hmmph!

At one point, I had thought that tightening down the superheater might have distorted the boiler top plate and made the tubes lean inwards. No such luck - life is never that easy!

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