Crankshaft is the main rotating mechanism of the engine, which is responsible for converting the up-and-down reciprocating motion of the piston into its own circular motion, and what we usually call engine speed is crankshaft speed.
Camshaft is called overhead camshaft in English, or OHC for short. There are three installation positions of camshaft in general engines: lower, middle and upper. Overhead camshaft is to put the camshaft in the cylinder head and above the combustion chamber, and directly drive the rocker arm and valve without a long push rod. Compared with the pushrod engine with the same number of valves (i.e., overhead valve structure), the overhead camshaft structure requires far fewer parts to reciprocate, thus greatly simplifying the valve train structure, significantly reducing the engine weight, improving the transmission efficiency and reducing the working noise. Although the overhead camshaft makes the structure of the engine more complicated, it brings better comprehensive performance of the engine (especially the significant improvement of ride comfort) and a more compact engine structure, which makes the engine manufacturers widely adopt this design in their products soon. The driving modes of overhead camshaft and overhead valve structure are not necessarily different. Power can be transmitted to overhead camshaft through timing belt, chain and even gear set.