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Poppet Valve Engine - Steel Cylinder Head

|Crank | Crankcase | Cylinder | Cylinder Head | Cylinder Liner | Flywheel | Spark Plug | Timing Gears

Nigel Taylor

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.


Index Page for the Poppet Valve Engine

If you have made a similar engine and would like to share your experience we would love to hear from you - ed.