No.18’s, Lewin, first movements under steam last year were slightly tinges with disappointment over the very poor performance of the engine and the near constant roar of steam up the chimney.  Clearly all was not well with the valves and though the slide valve had received attention, likewise the valve rods, the port faces had not.  Close examination revealed them to have both pitting and a concave surface that allowed steam into both ends of the cylinder at the same time – whence the indifferent performance.  Over the many years of use, the valve had worn an arc into the port face, and whilst they remained worn together, the fit was ok.  But once the valve was machined, it was true (flat) but the port face was not – leaving as much as 20thou gap as well as steam escape routes via the pitting.  Much contemplation then took place, with the inevitable conclusion that the port faces would need attention.  The challenge here is that they are accessed from above, in a confined space and almost certainly inaccessible to any machine tool or boring head.  Originally the castings were probably only hand finished, and so this was the option chosen and Dave Young kindly (heroically?!) offered to have a go at the job.

One week on, he has more or less completed the right hand side chest, though the valve will require truing up to the new port face to give this work the best chance of success.  Here, in photographs, is an illustration of the work carried out:

Below: Using a true flat plate, engineers blue and a feeler gauge, Dave demonstrates the clearance evident between plate and port face.  This is now down to 3 thou from 20thou and the overall surface area is much flatter than had been the case before, where the years of movement of the slide valve had worn an arc as the gland bushes had opened and worn to allow the valve rod to become sloppy.

Below: A view looking down into the right hand side valve chest, showing the port face and the steam and exhaust ports clearly.  What is harder to see is that the surface is now much flatter than it was a week ago, care of 25 hours hard work by Dave and his dreadnought file.  Iron dust is visible from the exertions so far, likewise a few traces of blue.

Below: Dave, with a toolkit of home-made items for reaching into the awkward valve chest, contemplates the next phase…

Below: The homemade tool, a dreadnought file with wooden handle, as used in the confines of the chest, to great effect.

Now that this side is more or less complete, the trickier left hand side remains to tackle.  More of this next time…