|Aircooled RD350 engine, late model electronic ignition|
|Wössner RD350 two-stroke piston - work of art|
|Modified RD350 cylinder head with a 12.5mm squishband|
Now the 2.2mm gap could quite well be intentional, as these heads could have been fitted to a race engine, which was running both without a basegasket and had the cylinder itself shortened by the height of the headgasket relieve. Yet this is not an excuse for machining the head too small and also for the headgasket.
|Headgasket 1.35mm thick|
|A stock RD350 head and combustion chamber (for comparison)|
Now here are two schools of thought. If you machine a very steep angle into the head (as seen in the picture above) the mixture will travel to the spark plug without being compressed overly much. It will do so, but not in a very fast way (still heaps faster than stock, but you get the idea!) Now if you used a very shallow angle, let's say around the 3 to 5 degree mark, the charge would be pre-compressed, heated up and would burn a lot faster, because it has already picked up a lot more speed.
There's many ways to actually measure the distance from piston crown to the roof depending on the size of the gap. In this particular case the distance was too big to use solder or twisted strands of solder, so I had to resort to some sort of clay in order to get the cylinder heads in the right ball-park to start with.