Reboring The Cylinders of HMAS Foden

Just read Ray Freemans article on reboring the cylinders on a locomotive. I brought memories of a similar job I did on the Foden Steam truck back in 1976/77. The old girl (I was never politically correct) was having trouble performing on the road, particularly up hills. We decided to have a look at the cylinder bores and valve faces.

It was too long ago to remember bore sizes etc but I believe the High Pressure cylinder bore was about 4 ½ inches diameter and the low pressure cylinder about 7 or 8 inches. Stroke was around 8 inches or so or perhaps even as long as 12 inches.

Tools available was a REPCO automotive cylinder boring tool (electric) Horizontally mounted on the engine block. But of course our cylinders were horizontal. The capacity of the tool with all it's attachments was for a maximum bore of about 3 ½ inches and a stroke about a ¼ inch too short for our needs.

We mounted this heavy machine onto the face of the cylinders using clamps and ordinary brown wrapping paper between the mounting surfaces to prevent slippage once mounted. (this is an old fitter machinist's trick, it provides much more grip between the metal mating surfaces and the paper is of a uniform thickness)

To overcome the boring capacity of the machine we just made our own boring bars to suit the job. One for each cylinder. ( the facilities of a Naval Engineering College come in handy at times)

After boring the cylinders the remaining rim left by the limited "reach" of the machine, were hand scraped out to size. The Navy taught as to do things the hard way if we had to. The pistons were built up to size and re-machined. New rings were machined from Spun Cast iron and fitted to the pistons. Spun Cast Iron is so called because it is poured into a spinning cylinder while molten and forms hollow "pipe" of cast iron when it hardens. This process gives a casting witch gives excellent strength when used for making piston rings. Cast iron has what was called "grain" as in wood grain an to achieve the max strength in this application you need to use Spun Cast Iron so that the Grain runs around the Piston Ring and not across it

I recall that after machining the rings (a fraction oversize to allow for a tight fit after cutting the diagonal join to allow them to be fitted over the piston) it was quite difficult to spread the rings sufficiently to fit them over the pistons. And, for cast iron, had a lot of stretch capacity without distorting the ring at all.

The valves were repaired by machining the mating surface flat and manufacturing steel plates to fit with the necessary ports cut into them and screwed them to the original valves with countersunk screws and locktited them in.

Reassembled and test run she was much improved

Regards Tony Middleton tonymiddleton@orion-online.com.au