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Originally I started with an Aluminium Cylinder Head, but after a hours of machining I abandoned it.....
The cylinder head was just not correct and so I started again and this time made it from mild steel.
From underneath you can see that I have at this point increased the depth of the part that fits into the cylinder liner.
This engine is being designed as I go and so this may get machined back when I look in detail at the spark plug and valves.
The inlet and exhaust ports now machined and a starter for the plug.
The plug now comes in from the side with a 10° angle downwards.
The relief for the plug was at first slot drilled with a 6mm mill, it was then centre drilled as this allowed me to ensure that the hole was bang on centre and did not move.
I then used a 5.3mm drill which is the pilot size for the 1/4" x 32 thread. I then used a 12mm slot drill to allow clearance for the plug so that I could tighten it.
The slot in the underside of the head is just an initial slot to get access to the plug, I believe I will need to open this out to 6mm diameter.
The inlet port is at the rear of the head.
This is tapped 6x1mm so that I can fit a short inlet pipe and carburettor.
In order, I used a 6mm diameter 2-flute slot drill, then a 1/4" centre drill to mark a pilot hole, I then drilled a 5mm diameter hole, then used an end mill to take this out to 8mm diameter and 6mm down from the outer surface of the cooling fin.
If you have made a similar engine and would like to share your experience we would love to hear from you - ed.