Cylinders 3
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NEW 6/03/03
With Alastair busy on the valves I turned my attention to the remaining cylinder bits that required turning. The first job to be tackled was the cylinder covers. These are cast with a chucking spigot - so the first job was to turn this spigot somewhere near true. The outside edge of the castings were held in the 3 jaw to do this. Incidentally I tried machining one cover without first truing up this spigot - not to be recommended!!!
The covers have a register which fits into the end of the cylinder bore. These were turned to match each individual cylinder to ensure a good fit was obtained. At this point the holes for the piston rods were also drilled and reamed to ensure they are concentric with the registers.
Having turned the inside faces of all the covers the next job was to turn the outside faces. The front covers are recessed to look nice while the rear covers have a nice flat bolting surface machined, along with the front of the gland box. To hold covers a split ring was made up which simply compressed when the lathe jaws were tightened and held the workpiece securely.
Having completed all the turning work on the end covers I turned my attention to the pistons and their rods. The pistons were made from a length of 2" dia cast iron which we had left over from another job. This was turned down to just oversize, and then drilled and threaded.
The next job was to make the piston rods. These are a piece of 1/4" dia stainless threaded at one end. The pistons were then screwed onto the rods. The die was left slightly so open so the thread was very tight - there's no way they are going to work lose!
The rods were now setup in the 4 jaw and set to run absolutely true. The pistons were now turned to the diameter of the bore - 20 thou. This ensures that the rod and the pistons are absolutely true. The final job was to make the grooves for the piston rings. A tool was ground up and then fed in very very slowly - the result couldn't have been better!
