My working knowledge of two strokes?--Well, they have piston, rings, connecting rod and crankshaft similar to 4 cycle engines. They do not have a camshaft nor valves. The crankcase is closed and will hold pressure. They combine the strokes--When the piston is moving up on compression, it creates a vacuum in the sealed crankcase. The carburetor feeds into the crankcase thru a one way valve, most commonly a piece of very thin spring steel called a reed valve. The lubricating oil is mixed with the fuel, so as the fuel enters the crankcase it lubricates the crankshaft bearings and both ends of the connecting rod, and the cylinder wall. The engine is fired by a sparkplug at or slightly in advance of top dead center and the piston begins to move down in the cylinder on the power stroke. As the piston moves down in the cylinder, this raises the pressure in the crankcase, and the reed valve under the carburetor snaps shut so the pressure in the crankcase can not escape. At some point in it's downward travel, after most of the burning fuel charge has expended it's energy but the piston is still moving down, the piston uncovers a port in the side of the cylinder which is connected to the pressurized crankcase. The fact that the fuel charge in the crankcase is pressurized makes it flow from the crankcase, thru the port in the side of the cylinder, and into the cylinder itself. At this point, the piston bottoms out and begins it's upward travel on the compression stroke. The side of the piston first closes off the port in the side in the side of the cylinder so that the charge of fuel which is now in the cylinder can not escape back into the crankcase. The piston then continues towards top dead center compressing the fuel charge and once again creating a vacuum in the crankcase to draw in more air/fuel mixture. Then the cycle repeats itself. The two cycle engine fires every time the piston reaches top dead center. From what I remember, the top of the piston is not flat, but has a "shape" to it which has something to do with keeping the burning fuel charge from blowing back thru the port into the crankcase---(I could be wrong on that reason.) ----So much for the theory behind two cycle engines.---Like everything else in life, the devil is in the details. If the piston has rings on it, how does it pass a port in the side of the cylinder without breaking the rings? How far down the stroke of the cylinder is the port so that it optimizes the power from the expanding fuel charge and still allows some time for the pressurized charge to flow upward from the crankcase into the cylinder. Would a model engine require seals on the crankshaft where it exits the crankcase, similar to 2 cycle snowmobile engines. (I once had a Yamaha snowmobile that had bad crankscase seals--it would go like stink at high speed but stall every time you slowed to an idle.) I know that there are many variations to what I have described. I know that the Jan Ridders design pressurizes the fuel charge in a separate compartment. I also know that two cycle chainsaws and weedeaters have flat top pistons, and I'm not sure how they get away with that. So you see, I know a great deal about 2 cycle engines. that is the good news. However, there is a great deal more that I don't know about 2 cycle engines, and that is what keeps me from boldly jumping into the design and fabrication of an engine which is doomed to failure because of the things I don't know. If I do this at all, I would much rather follow in someone else's footsteps.---Brian