[Christ]

Originally Posted by dcb

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).

Rotary engines work that way, too, but not like the illustration you provided.

There is an ellipsis lobe on the crankshaft (called an eccentric shaft) on which the rotors act to create rotational inertia (torque).

They make a similar type of contact as a cam does with it's followers, except that the rotor is always side-loading the ellipsis, putting the most force at it's most susceptible tangent, whereas the cam's follower is not.