Progress report on restoration of steam locomotive General Steam Navigation

The General Steam Navigation (GSN) Restoration Society has released its latest update on the restoration of Bulleid Pacific Merchant Navy Class steam locomotive No. 35011 General Steam Navigation.

Boiler

Inside the firebox, work continues on the boiler, with the last of the remaining boiler tube stubs removed last month. Rust is being removed rust from inside the firebox, the inside of the boiler is being descaled, and the inside of the boiler and firebox are being cleaned ahead of a planned inspection.

Crank Axle

Progress is continuing on designing the crank axle, and the original drawing has been converted into an electronic CAD file. The next step is to design the chain-driver sprocket and to start conversations with a forger and manufacturer to develop forging and manufacturing drawings. Together with design work for the new crank axle, thoughts are turning to the balancing weights. Rebuilt Merchant Navies had external balance weights on all three axles, but it is planned to remove the weight added in 1958 on the leading and trailing axles and to rebalance the wheels, with weight in the pockets if possible.

The shape and material of the coupling rods still needs to be decided, which will impact the amount of balancing needed on these axles. The aim is to emulate the classic Bulleid appearance with no visible balancing.

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Originally the crank webs and inside connecting rod for the central driving wheel were balanced on the wheel rim, with a large plate on the rear face of the wheels and lead in the pockets. By studying the designs for the original and rebuilt locomotives, the team now knows how to rebalance the driving axle.

From a mechanical perspective, the leading and trailing wheels won’t need rebalancing, although from an aesthetic perspective, it is planned to do this. It is also planned to fit plain rods as were fitted in 1956 since they have greater tensile strength and are less prone to bending. The next step with the balancing is to determine the disposition of lead in the pockets to achieve the desired counterbalance. For the leading and trailing wheels, this is little more than a tweak to the original design, but the central wheel needs further design work to determine the centre of gravity of the lead pockets and the balance weight plate.

Frames update

The five large brackets that held the external valve gear and screw reverser have been lifted off the frames. These are now surplus to requirements, as it is planned to construct Bulleid’s chain drive valve gear and fit a steam reverser. Removing them made it easier to access other areas of the frame, and the last of the brake blocks and arms have been removed from the leading and trailing axles.

All of the parts hanging off the frames will be removed later this year, which will allow the frames to be lifted, releasing the leading bogie, leading axle and trailing axle. The leading bogie will then be assessed and prepared for professional restoration to mainline condition, whilst the driving wheels will be sent to South Devon Railway Engineering for rebalancing and profiling.

There is a need to clean and review the present condition of the frames, and cut out and replace any corroded sections of the framework, rear platform, and dragbox. It is also necessary to reverse some of the areas that were changed during rebuilding to allow a new middle cylinder to be installed and Bulleid’s unique patented chain-driven valve gear to be replaced.

In order to help fund the work on the frames, a Funding the Frames appeal has been launched. All money donated to the appeal will be specifically ring-fenced for the frames. If you can contribute to this project in any way, however great or small, the society will be grateful for your support. You can find out more here on their website

You can see the latest video update below

University Project

The society has a university project looking at the Internal Aerodynamics of a Merchant Navy. It is building on lessons learned last year, as well as a better understanding of test data that is available on both the original smokebox and the rebuilt design. The project is looking at variations of the original exhaust design and variations on a Lempor exhaust to understand the impact of nozzle size, angle, and target on the smokebox draught.

As part of the project, a visit was arranged for the students to visit Loughborough shed to examine 34039 Boscastle.

2022 is going to be a very important year for the project with some big goals in mind. To achieve this, the society needs your help.

If you wish to become a Society member, you can sign up for membership for currently only £15 per year here on their website.