April 04, 2013

"Thompson B3/3 from a whole host of spare parts..."

I'm not even going to pretend that this particular build is anything other than using as many spare parts and different components as possible to make something which, in reality, did more or less the same thing!

I mused on building Thompson's lone, short lived B3/3 locomotive a while ago, but with the arrival of a set of 6ft 9in driving wheels (actually standard Hornby Royal Scot spares), I decided to push it up the queue a little bit to see if the idea was a goer or not.

The answer is...yes, it's definitely a goer. So much so that it's jumped ahead of quite a few projects whilst I'm developing it further!

I have fitted the new driving wheels, which required re-quartering on two sets to the proper configuration, along with the correctly sized brass bearings from the Hornby B1 chassis' wheels. It is somewhat infuriating that the Hornby Royal Scot and Thompson B1 share axle sizes, but not, apparently, the brass bearings. Try as I might, I could not get the set which came with the Royal Scot drivers to fit the chassis, but the B1 bearings fitted first time with the Royal Scot drivers. The result is a working Hornby B1 chassis, re-wheeled with 6ft 9in wheels.

In order to get the wheels to fit good and proper, all of the brake hangers plus any other details such as the sanding gear, need to be removed from the bottom keeper plate and surrounding area. I have kept all of these moulded details for reuse later on in the build (the brake blocks, in particular, can be simply repositioned to fit properly).

Stunningly, all of these modifications have helped to give me a chassis which is only 1mm out on for the actual wheelbase of the B3/3, and that's on the rear drivers which are 1mm too far backwards.

I think I can live with that though, as the front end is absolutely spot on, both for the level and inclination of the standard B1 cylinders, and the placement of the valve gear. I really did not expect it to be fit quite so well as it did!

The next job on the chassis is to fit new brass pickups. Fitting larger wheels meant that the brass wipers already on the bottom keeper plate, would not be long enough (larger diameter, longer distance to circumference of the wheel where the pickup meets the tyre). I therefore need to make some bespoke ones. In order to test the chassis, I simply attached the red and black wires to the terminals of my Hornby rolling road. It ran smoothly through all of the power ranges, and in reverse too.

The driving wheels will need new balance weights to be fitted (it is likely that thin plastic overlays will be the order of the day) in addition to refitting the brake blocks, hangers and similar along with the sanding gear, and as mentioned previously, rewiring and making new brass pickups before the chassis is complete.

In the body stakes, I've discovered a very interesting fact. The B3/3 had its B1 boiler pitched higher than the Thompson B1, with a shorter chimney and a squarish Gorton dome fitted, but the cab and the boiler fittings at that end remained in proportion to the boiler, as per the B1.

This meant that the high shoulders on the B3/3 are actually deeper than on the B1, and at the rear, the running plate dip under the cab is deeper too. The cab itself is longer and deeper, although the roof remains the same more or less. In theory, cutting and shutting two Bachmann B1 bodyshells should give us the correct length running plate at both ends, and cutting and shutting two cabs will give the deeper, longer B3/3 cab.

Obviously the above is by no means a finished picture, but it's an interesting amalgamation of components to present my progress on the idea. That we've got a working chassis (albeit minus pickups at the minute) is a great starting point. I sincerely did not think it would be this easy to simply replace the driving wheels and refit the valve gear!

I've quite a bit of work to do on my other outstanding projects. The Ivatt N1 needs coal rails, Great Northern needs her running in before a coat of blue and transfers (but the nameplates have arrived!) and I've got to finish that Railroad A3 conversion before the end of the month. The B3/3 will fit in and around those projects as they come to completion.

I've also got a layout related update coming up this month, surprisingly!

Until next time, thanks for reading.


Anonymous said...

This is a very interesting one Simon. I'd no idea of the existence of the B3/3. From the high-stepping appearance it looks like you'll have a lot of boiler fitting hacking to do!

Copley Hill said...

The boiler itself needs virtually no alteration. A shorter chimney and a replacement gorton dome is all that is required, as it was a standard B1 boiler simply placed onto the B3 frames.

This means the B3/3's boiler is pitched higher than a Thompson B1, which explains the necessity of a shorter chimney and the flat topped Gorton dome.

Where all the cuts have to be made is at the front and rear ends, for the front "shoulders" need to be deeper by 1mm and the same at the rear by the cab, which also needs to be lengthened to accommodate the longer cab.

Looking at the B3/3 photographs more closely, it must have been a very imposing machine, and it's quite handsome in itself. It's described in several accounts as being very smooth running but suffering from frame cracks more than other locomotives.

Anonymous said...

hi Simon I don't want to be a pain but I dropped a couple of questions on the last post and I was hoping you could take a look at them