Part 17 By Vince Cutajar

I chucked up a piece of 65mm aluminium stock and partially parted a piece off. In the same setup still using the parting tool I cleaned up the sides of the disk. Then I hacksawed the disk off and faced off and cleaned it up. I left a mark of the centre on the disk.

Starting from the centre of the disk and using the DRO and the same distances between the holes, drilled, reamed (4mm) and countersunk the four holes. The cylinder head was bolted to the disk and the whole assembly held in the 3 jaw chuck. The bottom of the cylinder head was faced off to dimension.
For the combustion chamber, I marked out the two diameters I needed and milled it out first with a 15mm slot drill and then with a 20mm end mill. Then continued with a boring bar.

Using the same boring bar I turned the shallow groove to fit the cylinder liner lip. I actually used the cylinder liner lip as a gauge. Depth was adjusted just to leave a hairline space between the cylinder and the cylinder head.

I left a centre mark in the combustion chamber just in case I need it later on.

Machined a fin from solid in the bottom of the cylinder head. Used the same parting tool I had used when I did the fins in the cylinder.
The engine is starting to take shape.
Cleaned up the sides of the cylinder head. Used the centre mark I left on the top of the head as my datum. I first did one side and then the other side.
Made another fixture for the cylinder head. Similar to the previous round one, but this is rectangular. I drilled and counterbored the holes around the centre mark (barely visible) of the rectangle. I also changed the 4mm tapped holes in the head to 4mm clearance holes. I screwed in the 4mm tap in the threaded hole clamped the tap in the drill chuck and clamped the head to the mill table. This to align the spindle to the tapped hole.
With the head bolted in the rectangular fixture, I clamped it in the vice and using the centre mark I left on the head and the DRO I marked the holes for the valve guides and the rocker arm pillar. I also marked for the port holes in the flanges.

Drilled and reamed 5mm the valve guide holes and also drilled and tapped 6mm fine the hole for the rocker pillar.

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