The geometry between a piston, piston rod and a crankshaft in an IC engine appear to leave a lot to be desired since the gas expansion only acts on the crankshaft in any usable sense for about 35 to 40 degrees of rotation. And never at a 90 degree angle. The side loads etc would have to be absorded by the casing meaning a more robust structure. It seems to me that a cam arrangement would be more advantageous since the piston thrust would act on the cam at 90 degrees for a much larger part of the crank's rotation. So the question is, are they are more effecient, and if so, why don't we see them in production?