Sunday, 30 November 2014

No Longer a Screw (too) Tight!

Sentinel 7109's new chimney castings, having been machined to have flat bases, need a nice flat boiler top surface to sit on. Sounds simple enough except that lately I'd begun to wonder about the actual flatness of the boiler top plate on which the castings would come to reside. So one day I took along a straight edge and looked a bit more closely.
A Sinking Feeling
It was clear from the straight edge that all was not quite as I'd hoped and that there was probably 1/4" sag in the centre at the point where the superheater was supported.

Even more closely:
Another Sinking Feeling
And the other way:
And Yet Another
As the lowest point seemed to be where the superheater's support was located, I surmised that perhaps the superheater might have been tightened down so much that it was distorting the top plate.

Whether it would be possible for the top plate to be flattened simply by screwing both chimney bases down tightly, I did not want to entertain in case a casting cracked in the process.

I then checked the effect of loosening the superheater support (where the two nuts are). Indeed the sinking could be lessened to 1/8" instead of a 1/4" which I felt would be satisfactory.

It's clear that it will be better to slacken the superheater support and tighten down the chimney castings first to make the top plate flat. Then tighten the superheater with the chimneys in place.

Nice idea but see the picture below:
Space between the old chimney bases
The new castings leave even less space between them than the old castings shown above so it will not be easy to wield a spanner in there.

But where there's a will...

Tuesday, 25 November 2014

No Longer a Screw Loose!

I confess, this is not going to be one of the most engrossing articles on Sentinel 7109 but a very short piece to record which one of the chimney castings' fixing studs needed to be welded in place to the boiler top plate. It was the one in the photo below.
The regulator is at the top right.
So, when looking to the front from the rear of the cab, the stud is the rearmost outside left hand one...
...the hidden one at the bottom left near the spanners!
A few years ago, when the top plate was refurbished and the fixing holes rethreaded, this stud was so loose, it was more likely to pull itself out than hold down a chimney. Hence the reason for the welding.

Now, just to show off a little, even I felt I'd surpassed myself with the tidiness of the weld itself. No angle grinding was used at all to cover mistakes.

Since it was always going to be a very small weld, I judged that using a stick weld would add far too much metal and need grinding away afterwards to tidy it up leaving iron filings all over the place to rust. It would also be very difficult to wield the stick in such a confined space above the boiler. So I decided to use a TIG torch.

It was still not an easy task as, not only did I have to get the welder in the cab but an Argon gas bottle as well. There really is very little space in this cab!

It was a good decision, however, as the top photo shows.
Related Posts Plugin for WordPress, Blogger...