When drawing up the engine I played with a few options for the cylinder. I did think of doing an aluminium finned outer with cast iron liner but it would not have been easy attaching this to the frame and the same problem would have existed if I went with an all cast iron option. In the end I settled on a steel finned outer which could be silver soldered into the frame that would also accept a cast iron liner.

First job was to saw of a length of EN1A steel with sufficient length to allow it to be held in the 3-jaw while a spigot was turned to locate it in the upper part of the frame. Here you can see me using the frame to gauge the fit.

Then with some added tailstock support the fins were roughed out using a 2mm GTN type parting insert.

Changing to a 2mm dia MRMN tool the sides of the fins were tapered and the valley rounded to give the ‘cast’ look.

The chucking piece was then sawn off and the cylinder outer bored and a spigot cut to locate into the lower part of the frame.

The next job was to make the various webs that stiffen the frame, these were located into shallow slots milled into the inner faces of the frame and shaft bosses, here you can see a couple in place; the crests of the fins have also been rounded over.

After completing the webs and adding more bosses for the valve guide and fan spindle it was time for a bit of silver soldering.

I could now treat my fabrication as a casting. After sawing out the spacers between the bosses the inner faces were milled back to length then the frame held flywheel end upwards and the shaft holes drilled and reamed. If you look closely particularly at the cam shaft boss that I tried to hide with the milling cutter you can see that things moved slightly during soldering but that protruding boss is due to be flushed off so won't show.

The bottom was given a quick skim and the mounting holes added.

I opted for off-the-shelf gears as they are cheap particularly as they were wide enough to cut down the middle so I have some for the next project; some makeshift shafts were slipped into the holes and gear mesh checked out okay.

Part one here  Part three here