Part 18 By Vince Cutajar

Using a long reach 8mm ball nose mill I started work on the port holes. Started with the horizontal holes. Clamped the head in the vice. Centre drilled and drilled 6 and 7.5mm. Then reamed 8mm and then used the ball nose mill to give it a radius at the bottom of the hole. For all these operations I used a collet holder instead of the drill chuck. I also faced off the flanges to the desired size.

Bolted the head to the rectangular fixture upside down. Located one of the valve holes with a 5mm silver steel in a collet. Clamped the fixture to the mill table. Drilled 7.5mm and the reamed 8mm. Using the new 8mm ball nose radiused the bottom to match the other horizontal hole. For the valve seat I used a countersink tool.
Finished the other hole and valve seat.
Next made the flange template/exhaust flange from brass.
For the spark plug hole, set the head up in the vice at 60 deg. With this setup I can see where the drill is coming out in the combustion chamber. I did not follow Westbury's method because I could not picture it and it involved trial and error. Milled flat the spark plug face. Picked up the centre of the head from the mark I had left and marked the line on the freshly milled face. Did not find a way to mark the other line to get the centre of the hole. So I put a 14mm end mill in the chuck and eyeballed it. Drilled the hole in steps of 1mm all the time checking the bottom of the head. At 7mm decided to move the X-axis 0.1mm to one side and used an 8mm slot drill to continue. Drilled 9mm and then tapped 10 x 1mm. Did not go right through with the taps.
The spark plug in the head.
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