One of the many constant challenges for the workshop staff at Belgrave is being able to create and maintain an air tight seal around the smokebox door. A poor seal which allows an ingress of air will cause the vacuum created by the action of the exhaust steam to be destroyed, thereby eliminating the draw of air through the fire and ensuring the engine won’t steam. Any localised overheating of the smokebox door will cause distortion, serving to compound the problem.

Having heard good things from some of our contacts on the Welsh narrow gauge railways about seals utilising fiberglass packing rope, we set about designing a new smokebox front plate and modifications to the existing door in order to try it out.
The existing front plate was found to be excessively corroded so a new smokebox front plate was profile cut and machined, and a plate ring was rolled and welded around the inside of the opening.

A similar ring was rolled and welded to the inside of the smokebox door, forming a cavity into which the fiberglass rope was packed. The ring attached to the smokebox front plate aligns with this cavity, forming a seal against the packing rope.

All the studs in the smokebox had to be replaced, so were ground off flush and drilled out, following which, the new assembly was fitted and issued to the Loco Operations Department for evaluation.