Not much to say about machining flywheels that I have not said before. Five Spoke layouts are always a pain to hold as you usually can’t get 3 or 4 jaws inside the rim without the spokes getting in the way so I mount them on a faceplate with a bit of 6mm MDF between. That way I can completely turn the face, one side, the hub and bore all in one setup. The hub was bored using a piece of the 12mm PGMS that will form the crankshaft as a gauge.

Here they are slipped into position to get a feel for how they will look. The columns have also been made which are just tapered shafts with threaded spigots on the ends.

The cylinder jacket started life as a piece of 55mm dia EN3 and was roughed out to shape, the short spigot on the end will locate in the entablature plate.

With the boring bar held at an angle and coming in from both ends the middle was hollowed out to form the water space

There are two small webs at the base of the water jacket, these were formed on the corner of some 5mm plate and then the mill used to cut them from the plate.

here they are stood in place on the entablatur eplate which was cut from over thickness 6mm material, drilled and the central hole bored to accept the cylinder jacket.

The water bosses had there oval profile cut on the CNC, a boring head was used to do the concave cuts to suit the jacket and a holes drilled so they could be screwed in place to solder.

After a pickle the bottom of the entablature plate was faced down to it’s final 5mm thickness.

Then the top was faced to length, both ends bored for the liner and although it is hard to see there is a 1.5mm x 1.5mm rebate to take the lip of the liner.

Lastly the water bosses were milled off flat, drilled for water and tapped for the flange studs.

Thanks, Andrew, yes the flywheels came out very nicely and needed very little clean up.

I toyed with the idea of making a pattern for the cylinder head but in the end took the cheaper option of cutting it from a slice of 65mm dia cast iron bar and letting the CNC cut the iron rather than wood.

The first job was to machine the underside of the head including a spigot to locate in the cylinder liner. I then moved over to the mill and tapped what will eventually be the clearance holes for the head studs so that I could screw the head to a holding plate to give easy access all round for machining. I also ctr drilled the position of the valves at the same setting.

Back on the lathe the valve guide holes were clocked in, drilled and reamed, the cavity behind the valve heads opened up and the seats cut at 45deg using the top slide which keeps everything concentric. I actually only needed to angle the exhaust valve seat but got carried away and did both!

Then onto the CNC, this image shows the contoured effect that the initial adaptive cuts leave.

Then various other paths were run to shape the “cast” surfaces and leave the “machined” faces flat and true

With the head still attached to the holding plate it was easy to hold on the manual mill for the last few operations which were mainly the inlet and exhaust passages and the tapped holes around those for flanges.

This engine has an atmospheric inlet valve where the vacuum caused by the descending piston opens the valve, this can also be used to act as a demand valve for the Propane gas that will fuel the engine by having the flat valve also cover a small 0.7mm gas passage.

The original would have had a water jacket cast in around the cylinder with the water space being formed by a sand core. For our models it is easier to have a separate liner that as well as forming the cylinder also closes off the waterspace. Here the OD has been machined and a steady is in use while the cast iron bar is bored to size. I leave a bit of solid material at the end so that the chuck will not distort the thin liner, this can be cut off afterwards and the liner faced to length.

The cylinder does protrude below the bottom of the entablature and as the liner would have been too thin I turned up a sleeve to add the additional thickness. It also allowed me to silver solder on a bush for a drip feed oiler. Liner, Cylinder jacket and sleeve were all a push fit and assembled with 648 Loctite.

Thanks Andrew, there is some more modern tech to come.

The two crankshaft webs were drilled and reamed on the manual mill and then the holes used in conjunction with some top hat bushes to hold the material on the CNC mill to profile the  counterbalanced shape. The shaft and pin were from 12mm PGMS and all silver soldered together

After sawing out the unwanted bit of the shaft and filing the ends flush slots for the gib head keys were milled in each end. Don’t panic; I did not mill the overhanging left-hand one like that. The small vice ensures that the crank remains in the same orientation when swapped end for end in the main vice which should hopefully mean the keyways and therefore the spokes in both flywheels line up on final assembly.

I had thought about having the gears 3D printed in steel but Graham Corry of Alyn Foundry kindly donated a pair of equal diameter 2:1 timing gears that had been maturing and developing his usual patina in a damp Welsh workshop for some time

After a bit of a cleanup and suitable modification of the holes I could put the crankshaft into the bearings with its gear in place and then holding the other gear on an arbor in the spindle set the mesh of the gears and zero the DRO.

The lower gear support bracket could then be drilled and reamed at this position.

Without disturbing the setup the columns, cylinder and head were assembled to the base and the roughed-out top camshaft bracket screwed into place so that too could be drilled and reamed for it’s bearing at the same DRO setting ensuring the shaft was true and vertical.

Five spoke flywheels are always a bit of a pain to hold. Usually I like to use a 3 or 4 jaw chuck to grip the ferttled casting by the inside of the rim but the spokes and jaws always clash on a 5 spoke layout. So the faceplate was used with a piece of 6mm MDF between it and the flywheel so I could machine the whole outer face, one side of the rim and hub and also bore the central hole to a firm push fit onto the crankshaft.

The castings were woth the cost with nice to machine grade 250 iron and no hidden holes or hard spots thought I will be painting the rims so not quite as critical as a bare finish requires.

And all plumbed in

The water tank started life as a length of 40 x 80 hollow box section. I reduced the thickness of the walls so that I could get a smaller external corner radius and then silver soldered on the top & bottom plates

The hot tube chimney was turned from stainless steel as was the angled burner holder. This is actually threaded internally to allow a small Sievert burner to be screwed in once it’s chrome end has been removed which gives a fairly compact arrangement that does not look too out of scale.

The engine stood like this for a few months while I got distracted with steam engines and also I did not fancy cranking over an engine in the hot weather we have had. I got back to it a couple of weeks ago and did the last few minor items which were cutting the face cam, making the rocker arm and plumbing in the gas supplies. It was then ready for a test run.

It was poping but as soon as it did the hot tube burner went out, I soon traced that to me having just done the hot tube up finger tight when it was made. The application of a copper washer and spanner soon had that sorted. After another few minutes of the odd pop I realised when I had timed the exhaust valve for some reason I set it as though it was the inlet valve. With that corrected compression was much better and the engine fired into life if a bit on the fast side. Sorry it is jumping about but I made the stand just to assemble the engine on and the screws soon pulled loose with starting loads.

With the engine now known to run it was time to make all the studs, nuts and scale fixings, a wooden base and apply some paint.

The stand was made from Oak and the mortice and tennon joints cut on the mill.

Next post should see it with some paint on.