there are actually engines with cam based crankshafts, dunno how efficient aside from less than 100%
, but if you manage the side loads without too much drag it works (rollers probably help too).
Internal-Combustion Cam Engines.
seeing this reminds me that
"Desmodromic" valves also address the spring bias problems, but it adds weight and manufacturers prefer a lighter valvetrain (you can use lighter springs and get more energy back from them that way).
