I have always liked the look of the Forest engine reproductions that Wayne Grennings produced and thought that I might have a go at a smaller one myself. Chances of getting the non compression carrier flame ignition to work at the smaller sizes even if I could make up a suitable cocktail of gasses was slim but I thought it may work as a flame licker using the proven mechanicals of my Chuky and Alyn Foundries Chuk as a basis.

Graham from Alyn had said that it would not be easy and he was right, I could not get it to run due to a few factors. Firstly the Evan's beam linkage of the crankshaft adds more drag, you can't easily get a clean flame with the shutter rods etc directly above and the biggest problem was with the can being so close to the shutter it tended to push it off the port face.

I had always had it in the back of my mind that if I could not get it to run as a flame licker it may be possible to convert to an air/steam engine with poppet valves much like the Jowitt engine I made a while ago. Even this was going to be difficult due to the lack of room so a couple of weeks ago I decided that a spool valve may work and made up the various part which resulted in a running engine.

It will run even slower than this but starts to get a bit jerkey as it is only single acting, at this speed it will run for at least 20mins on my small compressor without the tank needing to refill so not too noisy to run. It was an interesting project with a few more first crossed off the list such as first spool vale, first Evans bean and first spiral cooling fins.

The cylinder started out in much the same way as the Chuky with the ctr mark of the bore in the 50mm cast iron bar set to run true.

It was then faced, bored and a small spigot added to locate the cylinder head.

Reversed in the chuck the OD of the finned area was turned round and the end gently faced once the tailstock support had been removed.

Over to the mill and the port face was machined flat

Then to width

Followed by milling the port, this was sized for the flame licker version but could have been a lot smaller for the air/steam engine. I also had to subsequently drill and tap two M2.5 hols for the new valve block.

With a change to the horizontally mounted rotary table the rest of the lower part of the cylinder was milled round.

Now for the fun part of machining the spiral cooling fins. The rotary table from ARC has a 72:1 reduction so for ease of machining I opted for a 7.2mm pitch spiral which meant that for every turn of the hand wheel the milll table would need to move 0.1mm, as this was a bit coarse I opted for half a turn of the handle and 0.05mm x-axis feed per plunge cut of a 5.5mm 3-flute cutter. The two ends of the spiral were feathered out further with a 3.0mm cutter.

Just over 1000 plus plunge cuts later this is what I ended up with.

This picture shows the machining marks left by the plunge cuts which were cleaned up with a file and the whole "casting" given a once over with the Dremel to give it that cast look.

I think it could do with some legs next

Did not consider screwcutting as I woud not have been able to start and stop without run in/out grooves and approx 3.5TPI is beyond my machine.

I did briefly consider mounting my old Unimat 3 mill column on the lathe cross slide but by the time I had done that and sorted out gears and a leadscrew drive the mill was the easier option.

The "cylinder head" which incorporates the bearing supports started life as a piece of 5mm plate which was marked out and the bigger bits of waste material roughly sawn off. This was then clamped to a scrap of aluminium on the rotary table for drilling the various small holes and some to define the internal corners. Three of the holes were carried on at tapping size into the ali plate and then tapped so some additional screws could be used to hold the part while the main hole was bored.

The two clamps were then removed and the outside milled to shape.

The flame licker design needed a chamber for the spring and valve, this was bored out on the lathe and then transferred to the mill to shape the outside leaving a flat area into which the exhaust stack would screw.

Jumping forwards a bit the parts including two bearing supports have been silver soldered together, bearing caps screwed on and the assembly mounted back onto the ali plate to bore first the top bearing hole.

And then the other, in both cases the bearing was used to gauge the size of the hole

Hard to resist a quick trial fit

A bit of milling and the bearing caps start to take shape

Then roughing out the curved top which was finished off with a file

Final bit of machining was to drill and tap two radial holes for the legs to fix to.

A quick talking to with a grinding point in the Dremel knocked off all the hard corners and added a bit of texture to get the cast look.