Cylinder Update – August 2021

The machining of the two new cylinder blocks for 4709 is now well advanced at Roach Engineering at Brierley Hill in the West Midlands. As they are to be siamesed as a pair before installation in 4709’s chassis, the work is likewise being progressed with both castings being machined sequentially in stages, in preparation for their joining.

Wooden patterns ready for the foundry

This arrangement will ensure that machining operations are undertaken for each casting one after the other. With identical alignment for the first cylinder being used for machining the second, the team at Roach can ensure excellent dimensional repeatability, while saving significant time (and resources) by avoiding multiple set ups.

New castings for the front and rear cylinder covers are also in train and will shortly join the newly cast valve covers already at Roach. The work is progressing to programme with completion expected in early Autumn. The finished covers will then join 4709’s cylinders, ready for assembly.

The next step will be to mount the new cylinder assembly into the extension frames. This work will be carried out by and under the supervision of the Dinmore Manor Fund’s Mike Solloway at the Tyseley workshops. Mike lives in the Midlands and recently successfully fitted new cylinders to former GWR 2-8-0, 3850. His expertise with almost exactly the same process for 4709, will be invaluable.

The progress will see the front-end assembly offered up each of the extension frames and its mating cylinder in order to ensure precise alignment of all the bolting holes.

Cast, heat treated and now en route for machining

Once achieved, the cylinders are then bolted together upside down; the mating faces having been treated with sealant prior to the join. The extension frames are then final fitted to their respective cylinders and all of the newly machined bolts finally fitted. 

Only at this stage can the dimensions for the racking plate be measured, as it has to be installed to be a very ‘snug’ fit between the extension frames.

When done, this allows the racking plate/extension frame angle to be accurately machined, requiring very precise measurement to achieve the required standard of fit. Once all the numerous and newly machined bolts are finally in place, the two-ton leading centre stay can then be machined from site dimensions and it too finally fitted in place.

To complete the front-end assembly, the buffer beam will re-fitted. At this stage, the whole unit will be ready to be (re-)fitted into the 4709’s frames.