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I find some of your concepts difficult to understand, i believe it to be a language issue and illustrations would clarify your comments. i am having trouble with your high tension chain spark.Here's another idea, suppose that you moved the cylinder with a crank and con rod, so the spark plug location was kept between both pistons. you could mill a relief in each piston, and have the plug protrude half ways into the cylinder.Another idea is to make a piston with a partial spark plug inside it. the electrode would be at the center of the piston, and have an ceramic tube and metal rod that moves radially outward to where it brushes against a contact in the cylinder liner.The cylinder liner also has a ceramic tube and metal contact, so that when both contacts touch and the timing is correct the spark is fired.The advantage of this approach is that you could change the spark plug without tearing down the engine, since all that you would need to do is ensure that the cylinder plug is over the piston plug before unscrewing them. This is similar to how the wrist pins are removed on some subaru boxer engines.