Going to meet a guy in town here at Proturn Engineering. He used to machine “blanks pistons”, but these days the “blank piston” company, Ross Pistons, is doing all the machining themselves, so Richard is doing the designs these days and sends them of to the States.
But before I was going to see him I thought, make my own design, and we will see what he things of it, but I would say its pretty close.
So what I have done, I made two spacers, 5.7mm thick and rolled a piece of Plasticine. Then I used the bottom of the cylinder that has the steel sleeve sticking out to cut my “Plasticine disk”
I put the disk on top of the piston, and marked the Piston pin orientation on it (solid line).
Then measured the distance from outside exhaust valve to outside mixture valve (left to right side). Cut that off, and made a 30 deg ramp going inward. That’s the angle the valves are positioned. This makes sure the valves keep the same clearance as what they have now!
Finally I marked the spark plugs position (dotted line) 30 deg from center line for piston pin. Looks like 30 deg was a handy angle when they were designing the cylinder about 90 years ago !!! 🙂 The spark plug doesn’t really protrude into the combustion chamber, but this way there is some room for the combustion to start. The shape might change a bit possibly.
So this is what I ended up with (see below)
Now all the off cuts, I made a nice round boll of and decided to calculate the volume. And instead of sticking that somewhere, I calculated if I make the “disk” 0.2 mm higher, then the volume decrease of the combustion chamber is what I need to get a compression ratio of 1 – 7.
Looks nice and clean doesn’t it !! Will be interesting what Richard will say about it.