Problem with camshaft position

There are three types of camshaft positions: bottom mounted, center mounted, and top mounted. The camshaft of the lower mounted valve train is located inside the crankcase, the camshaft of the middle mounted valve train is located on the upper part of the engine body, and the camshaft of the upper mounted valve train is located on the cylinder head.
The engines of most mass-produced cars nowadays are equipped with overhead camshafts. The main advantages of the top mounted camshaft structure are fewer moving parts, shorter transmission chain, and higher stiffness of the entire mechanism, which makes the camshaft closer to the valve and reduces the waste of reciprocating kinetic energy caused by the large distance between the camshaft and the valve in the bottom mounted camshaft. Engines with overhead camshafts have faster valve opening and closing movements, resulting in higher speeds and smoother operation.