No, sadly I’m not talking about a visiting engine from a quaint narrow gauge line in Europe!
8A recently came into the workshops for attention, including leaking lens rings on the main steam pipes. Lens rings are essentially doughnut-shaped metal gaskets, forming a seal between concave recesses machined into two adjoining pipe flanges, whilst allowing for movement in the pipes caused by expansion and contraction, as a result of heating and cooling.
Closer inspection revealed that the mounting faces on the cylinder castings have become very thin over the years, as a result of corrosion caused by moisture in the smokebox (photo above). Previous repairs had been made, but any attempt to carry out further repairs to build-up these faces proved unsuccessful. At the same time, cracks were identified running down the steam passages into the cylinder castings which would have been virtually impossible to repair.
Followers of this blog may recall how 5 pairs of new cylinder were cast several years ago; failure of the castings was identified. Diving headfirst into fitting new cylinders would lead us firmly into the realm of the unknown, and highlight many variables which had the potential to see the locomotive out of traffic for months or more, not ideal as we heading for summer and peak season running!
With that in mind, rather than expend considerable resources trying to fit a set of new cylinders immediately to frames which are also original and nearing the end of their usable life, it was decided to affect a temporary repair to get the engine back into traffic.
Parallel to this, the engineering team will be producing drawing for the manufacture of new frames, allowing a frame/cylinder assembly to be built up before the locomotive is removed from traffic, thereby reducing downtime as much as possible.
New smokebox steam pipes (as fitted to 14A), including a section of flexible pipe which significantly reduces the tendency for the lens rings to leak, were already being manufactured. With a little speedy design work, these were modified (photo above) to meet a new penetration in the smokebox shell above the steam chest, where a flange was welded in place (photo below).
New steam chest covers were machined with a flange on top (photo below), and new external steam pipes were fabricated to complete the run from smokebox wall to the top of the steamchest. Whilst the addition of these pipes doesn’t hugely impact the aesthetics of the loco, it does create an image somewhat reminiscent of typical machines from continental Europe.
Hydraulic and steam tests, including a loaded run to Menzies Creek, went well and following some some minor cosmetic work, 8A returned to traffic where it is once more a firm favourite with the crews!
