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Little Wall

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I assume so as I only have scans of the particular article. It's the CS ending not X but could still be the same mag which could have altered it's name

Alyn Foundry:
I see you’ve found a use for one of those flywheels you made the pattern for Jason….  ;)

Oh no I haven't. They might just have done for the full size engine which was 4 1/2" dia  but the flywheel on this one is 74mm dia. No castings were hurt in the making of this engine ;)

Once the CNC work was done on the crankcase it was then just a case of treating it like any other casting and doing the easy bit of drilling and tapping the various holes and also milling a couple of clearance notches at the sides of where the cylinder mounts to allow the transfer of the air/fuel mix.

With that part complete I turned my attention to the end covers which are almost identical, the only difference being that one has a parallel area that the ignition timing disc can rotate on and the other at the flywheel end is as "cast". The first thing to do was bore out for the bronze bearing, turn the OD and also cut a spigot to fit into the crankcase.

Having previously carved out similar details for the Stuart Lightweight on the manual machines I again took advantage of having the CNC to shape the external pockets leaving the webs that support the bearing housing. First roughing out

Then a finish cut with finer stepover

When doing the CAM I had set it to leave 0.3mm on the bolting face so the part was returned to the mill and skimmed to finished size, as this surface was going to be left as bear metal the turned surface looked a bit nicer than the CNC milled one.

While the mill was covered in aluminium chips I also made the base, this was just drilled and tapped twice from below so it could be held to a smaller block which in turn was held in the mill vice. This allowed for easy access all round the part. Not so easy to see but the outer edge has a draft angle machined into it to more closely represent a casting.

The cylinder started life as a piece of 50mm dia steel bar, faced and ctr drilled for tailstock support so that the waste above the mounting flange could be removed. I did most of this with a parting tool then switched to a 1mm radius end grooving tool so that I got some fillets left in the corners as it was brought down to final size.

I then roughed out the cooling fins with the same parting tool and finished with the groover, this took a bit of setting up as due to the change in length of the fins the angle of each changed slightly as the spacing remains constant.

I used the CNC to cut the shaped holes for the inlet/exhaust boss and the simpler shaped transfer block

I also made use of it to cut the profile of the blocks on the ends of a bit of round bar, these were then cut to the undersize  inner radius of the cylinder using a boring head

A trial fit showed that the CNC had done a nice job with close fitting parts that just needed one or two strokes of a needle file and then they could be lightly tapped into place with a small nylon hammer.

Happy with the fit the parts were cleaned and fluxed before silver soldering together. After machining the inlet/exhaust boss to finished length it was back into the lathe to Finish bore the inside to accept the iron liner. Once that was done and there was no more need for a chucking piece the top of the cylinder was turned to profile and the M10 x 1 plug hole drilled and tapped. You can just see the every thin line of silver solder around the joint from the inside

The last bit of machining was t mill the slots for intake and exhaust and tap two holes M3 to hold the combined manifold in place.

Lastly I grit blasted the outside to remove any discolouration from soldering and give a good key for the stove paint I had planned for it.


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