5637 STEAM




Axle Stub Repair

The centre axle unit went away to Riley’s of Bury for essential repairs to be carried out. The failing axle was removed and replaced by a new one that started life as a raw billet of steel imported from South Africa. This was machined to size and pressed into place with a reported 100 ton force.

After replacing an axle it can’t be guaranteed that both wheels will retain their original relationship, i.e. still be parallel/square to one another. If this was not the case, then the whole axle assembly would need to be trued up on a wheel lathe. In normal service, all three sets of driving wheels would wear together at the same rate, however because the centre set had been machined to a new set of dimensions the other two main driving axle sets must also be re-machined to the new dimensions to ensure equal spring loading.

Thankfully for 5637 the two wheels did remain in alignment, but this does show that simple projects can have additional costs, as an expensive repair to the centre axle had not been anticipated in the early planning stages of 5637’s HGO. Just to give an idea of what the impact might have been, the Severn Valley Railway had to replace the whole centre axle assembly on a GWR Pannier at a cost of around £30,000 and 5637’s sister engine 6619 on the North Yorkshire Moors Railway has undergone a full centre axle renewal at a cost of around £50,000. 5637 got away lightly with a repair costing around £8,000.

Photo: : L.Thorp
The repaired crank axle and wheels

Axle Boxes

With the return of the centre axle unit back to the ESR, work could begin on aligning all six axle box centres, machining the horn guides back to square and flat relative to one another. Each axle-box was re-shimmed so it was not only centred in its frame with its partner on the other side but also maintained the correct dimensions to the axle-boxes on the other wheel sets.

It is crucial that the working clearances between the centre axle’s two axle-boxes and their associated horn guides are within a few thousands of an inch. The reason for this being that the pistons and their connecting rods are attached to the centre axle big end cranks. If there is too much free movement then the range of movement of a piston could be exaggerated and strike both cylinder covers causing extensive damage.







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