Reboring Locomotive Cylinders by Ray Freeman

Around December 2000 I had a phone call from a historical society in regards to on site line boring the steam cylinders on a Fremantle class Steam Locomotive. They had worn to the extent that so much steam was bypassing that the locomotive was not able to be used.

A time was arranged to inspect the job and in due course we had a look and did some measurements. On measuring the bores we found that from an original diameter of 15.875 inches there was up to .050" taper and ovality. Both sides were worn around the same amount. We were told it was possible to machine the bores till they "cleaned up" and oversize pistons and rings could be made to suit.

The next thing to tackle was mounting the line boring machine to the job. This turned out to be easy as around the end of the cylinders there was a PCD of substantial bolts around 11/4 inch diameter. We took some templates of these and had some 1 inch plate oxy cut on a profile cutter to match the radius of the cylinder ends. These were then drilled to suit the PCD. Once these were bolted on to the cylinders we could tack weld some mounting brackets on to attach our equipment to.

All this took time and it was early in 2002 that we arrived to actually machine the job. Setting up was easy as both ends of the bores were unworn. (The piston does not actually travel to the end of the cylinder.) We bolted on our brackets and attached a support bearing to each end of the cylinder. We then put a boring bar through the bearings and mounted a dial gauge to the boring bar. We then "swept" the bore and adjusted the bearings till we within a few thou total indicated read out. As the bores were around 28 inches long we decided to mount a centre support bearing half way along the bore. This was in the form of a spherical bearing mounted into a bushing with four jacking bolts positioned at 90 deg intervals. The bearing was installed in the bore and lined exactly to the other two support bearings by means of a piano wire. This was positioned to within .001 of alignment. The line boring machine was then mounted to the job and cutting commenced using tungsten carbide cutting inserts. We took the cutting slowly with out taking large cuts up to the centre bearing support with the last cut being around .010 to help ensure a nice round and taper free bore. At this point the centre bearing was loosened and moved into the freshly machined part of the bore. A dial gauge was again mounted to the boring bar and used to sweep the new side of the bore and the bearing adjusted to read zero run out. Machining was then started on the other end. When the last cut was taken we were pleased to see a perfect match in the middle were the two cuts merged. The bore was cut to exactly 16.000 inch. The opposite side was undertaken in a similar fashion with the sizes coming up the same.

Our line boring equipment is manufactured by Hofmann Engineering in Perth Western Australia. Is is powered by an electrically driven hydraulic power pack. This gives us a range of speeds from less than one rpm per minute to 240 rpm. Feed in either direction is provided by a variable feed box that can be either attached to the machine or else where on the boring bar. Diameters can be machined ranging from 1/14 inch to around 36 inches. When used for rebuilding worn bores the machine also does its own internal bore welding by using an attachment and a MIG welder.

My own background in on site machining goes back fourteen years and the bulk of our work is on large mining equipment.

After reading this article, Tony Middleton wrote to me again with another note about HMAS Foden. Tony remembered a similar situation regarding the Foden.