A nice simple job.
After all the fun and games with the crank and bearings, these were much simpler. The rough castings are turned to a rough oversize, and bored for the piston rods, and the first ring grove cut all at one setting (to ensure concentricity), then switched end for end (in the case of the HP one) and the other end (top) machined oversize too, and the 2nd ring grove cut.
IN the case of the LP piston, almost the same process was followed, except that it comes in two parts, which first get joined. This is to make the LP piston hollow and lighter.
Once the pistons are rough finished, and ring groves cut, then a dummy piston rod is made and used as a mandrel. Because this is cut and then used without removing from the chuck, and the pistons are mounted on it in the same way they will be fitted to the real piston rod, you can take a final skim over the outside (bore face/skirt) and know everything is true.
Lastly, a small file was used to gap the rings into the bore, and it all went together just perfectly! Time will tell!
HP and LP pistons with rings – ready to be fitted. A nice simple turning job.
SY Befur 
Fantastic progress and looking good.
thanks Nick, it’s true we are making progress, but slower than I would like. I have concluded that I am going to finish the engine first and then get straight on with the boiler – leaving the hull to the end. My original plan was to do metal work in the winter, and woodwork in the summer (being a better temperature for the epoxy work), but realized that this would mean having the car port full of boat for several years…. So sanity suggests this revised approach… Still agonizing about sail plans and superstructure – open launches are more attractive, but not in a squall on the solent, and I really fancy a Junk rig for simplicity of handling, but they are a bit “out of character” and more “in the way” when not in use – a gaff or sprit rig would furl more cleanly away…. decisions decisions…