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Single Overhead Camshaft (SOHC) engines have a single camshaft per bank of cylinders. Dual Over Head Camshaft (DOHC, also known as "twin-cam.") engines have two camshafts per bank. The first production car that used a DOHC engine was built in 1910.

A Single Overhead Camshaft uses adjustable rocker arms mounted on shafts to operate the valves. To check the valve clearance, rotate the crankshaft until the rocker arm is on the base circle of the cam. Measure the clearance between the rocker arm adjusting screw and the valve set.