Thank's John.

The next job on the crankcases was to mill off the last 0.5mm that I had left on the cylinder flange. To get things lined up I bolted a 20-40-80 block along the X-axis and clocked that true and with the ends of the main bearing and cam bearing housings against that the case was true in X&Y. A couple of 15-30-60 blocks supported the two mounting lugs.

The top was then opened up by drilling and then taken to final diameter and depth with the boring head. The four cylinder screw holes were also drilled and tapped M3 at the same setting.

Leaving the crankcases for the moment A piece of cast iron for the cylinder was turned down to the diameter of the fins and then held by this reduced diameter to face the end and bore out to 24mm

Before cutting a spigot on the end to locate in the crankcase.

Like a lot of parts I make one was used to gauge the size of the other, I think this fit is about right.

The cylinder was again reversed in the chuck and with tailstock support the slots between the fins were added with an insert parting tool

The last turning job now that I did not need anything too solid to hold by was to machine the waist between fins and mounting flange

As I wanted the practice on the CNC I used that to give the flange it's square shape with rounded corners and also drill the mounting holes.

That gave me an excuse for a test fit.

The last machining job on the cylinder was drilling and tapping for the head fixings, the spiral flute taps work just as well on crumbly materials as those that produce long swarf. Just needs a bit of honing to complete.

Thanks for the interest Ron.

Luckily I was able to keep the same 21/42 tooth count on the timing gears by using MOD0.8 which gave a suitable PCD distance. So first job was to machine the blanks, this is the larger gear that has had the faces recessed.

Unfortunately when cutting the teeth on this one the 4mm central hole was not upto holding it still and the gear crept on thearbor, it was also quite chattery. So another blank was cut but this time left flat faced and an angle plate placed against the blank so it could also be clamped to that with a toolmakers clamp and all went well. I also used 32DP cutters but cut to the MOD0.8 dimensions as there is so little difference between the two and I had the 32DP cutters.

The smaller 21T gear was not a problem having a 10mm hole though I did butt the angle plate up against the arbor to stop any deflection.

The large gear was then recessed and some weight reducing slots added more for looks than performance. Also in the photo are the two silver steel (drill rod) tappets and some bronze guides that I decided to include rather than having them run in the plain crankcase holes as shown on the original design.

The crankcases were then held in the mill vice and with a 10mm dia carbide cutter shank in the main bearings to support the small gear and the large gear mounted on the camshaft blank held in a collet the backlash was set and the DRO zeroed so that the holes for the camshaft bearings could be reamed in the exact position required.

All seemed to run smoothly enough .

With the holes done I split the crankcase halves so that the hole could be located on the mill and a recess opened up to give clearance for the cams.

Just a bit of EN1A for those as they don't really take any load and I'm not going to be running it for hours on end.

Each tooth cut in one pass then move on to the next, Andrew would slap my wrists if I did any different In fact they are quite small gears so probably less metal to remove than say cutting a 1.5mm wide slot with a slitting saw that is 1.5mm deep and being a smaller diameter than many saw blades the variable speed machine has a better mechanical advantage.

Ron, it's a fairly basic barrel carb and by having the jar lid as part of the barrel/spray bar assembly the lid and therefor the jar act just like a lever would on a RC model carb, I could also add a thin lever between lid and barrel if I wanted.

Couple of pics with the actual body removed so you can see the assembled parts that all rotate as one.

The crankshaft started out as a length of EN8 steel that was faced to length and ctr drilled for the throw and shaft centers before milling out most of the waste around the pin which is a lot faster and easier than turning it away. I left it for a week to settle after this but it did nor show any signs of having moved.

Then the pin and inner webs were turned, I used a boring bar for the left hand web and an HSS knife tool for the right, the pin was completed with a modified parting tool that has had the middle of the cutting edge ground away with a Dremel which stops any chatter as the tool is worked from side to side as a fine cut is put on.

I then rough turned the ends down using a holder that takes the "other two" corners of a CCMT insert while holding the web in the chuck.

Final finishing was done between centers using a DCMT insert which again helps reduce chatter and will also take off a fine cut.

I also turned and rough bored the flywheel at this stage but more of that later.

Last jobs for the lathe were to screwcut a thread on the end and then cut the taper for the flywheel, doing it at the chuck end makes it easy to bore the flywheel at the same topslide setting.

Finally back to the mill to shape the webs to give some counterbalance.

As I mentioned in the previous post before doing the taper on the crankshaft the flywheel was machined. first job was to recess the sides of a slice of 80mm EN1A steel, by setting over the top slide 2 degrees some draft angle could be included on the outer edge while turning conventionally.

Then buy running in reverse and working on the rear side of the hub that could have the same taper and by noting the topslide handwheel setting it was easy to machine to the correct depth. A tool with a rounded end was used to again give the look of an internal fillet as found on castings.

I could now set my topslide to the correct angle for the crankshaft taper and then use that to gauge the depth of the flywheel's tapered bore all without altering the angle so both tapers match. Fine cuts were taken until the shaft entered the flywheel and left 0.5mm clearance between the assembled bearing and timing gear.

Without altering the topslide angle I also machined a tapered arbor and pushed the flywheel onto that using a block and the tailstock ctr to make sure it stayed in place which allowed me to skim the OD to a true finish relative to the bore and cut the recess for the starting cord.

The arbor did not go to waste, with it held at an angle in an ER Collet block a slot was cut so that it could be used as a bush when broaching the flywheel.

The piston was turned from some 1" 6082 aluminium and a groove cut for a single Viton O ring.

I did all the hollowing out on the KX3 which was a lot easier and quicker at doing the "dogbone" shape than using the rotary table.

It was then just a case of cross drilling and reaming for the wrist pin before parting off and skimming the top.

The two halves of the conrod were taken down to overall size by flycutting the 2014 ali, the rod part was drilled and tapped, the cap drilled and counter bored for the screw heads. I made up a couple of sacrificial brass screws to hold the two parts together so that the CNC could do the outer profile in one without worrying about the screws. The big and little ends were done on the manual mill then a simple block with two tapped holes and a couple of tap hat bushes to holed the rod down and then press go.

Martin, this one was a bit slow taking just over 3 months start to finish but I generally don't spend as much time in the workshop over the summer so that is my excuse. . It's either too hot in there, garden and other interests keep me out and then there are the wasted afternoons hoping for an overtake in the F1. First photo I have of the crankcase is dated 7th July and it ran for the first time 13th Oct

Some of the other 24mm bore engines have taken about a month or if I happen to do one over the Chritmas – New Year period where I usually have a couple of weeks off then they can get done start to finish in that time.

The last major part to be made was the ignition timing bracket which was hacked to shape on the CNC

A few holes and a bit of filing and it was done.

Some brass hardware was turned and a steel screw to allow the clamp to be adjusted so the timing could be advanced or retarded and a couple of Corian insulators completed that assembly.

A piece of 8mm copper tube was bent to a pleasing shape and silver soldered to the previously machined flange to complete the exhaust.

In keeping with the age of the engine some slotted filester head screws were made up in M3, M2.5 plus and M2 one with an additional straight knurl for adjusting the carb slow running position. A single large but flat headed one was made to seal the oil level hole.

Not a bad collection of bits, 58 parts and 32 fixings.

After a quick test run to see if everything work the engine was stripped down again and a bit of colour added, in this case Dodge Orange VHT paint and some satin black stove paint for the exhaust. I also made the stands to display it on from a couple of bits of 1/4" thick aluminium angle that were pocketed out on the CNC.

With the photos out of the way I could run a few tank fulls through it and have a play.