Quote:
Originally Posted by cajunfj40
A simpler way of getting more leverage at peak cylinder pressure/TDC is offsetting the piston bore relative to the crankshaft, or offsetting the wrist pin in the piston. Basically, when the piston is at TDC, the crankshaft is rotated a bit beyond the point where the crank arm would be vertical. When peak cylinder pressure occurs, it will be working on a lever arm right away, rather than pushing straight down the vertical stack of piston/wrist pin/conrod/crank bearing/main bearing/main bearing cap, and trying to squeeze the oil films between those parts.
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Some motorcycle engines do this. And Nissan's new variable compression engine has the offset built into its geometry. Pretty neat bit of kit, that thing... a very simple and elegant way to get variable compression... and manages to minimize forces on the pistons to the extent that they claim to use much lighter conrods than normal engines.