Overhead Camshaft (OHC)

Some engines have the camshaft mounted above, or over, the cylinder head instead of inside the block (OHC "overhead camshaft" engines). This arrangement has the advantage of eliminating the added weight of the rocker arms and push rods; this weight can sometimes make the valves "float" when you are moving at high speeds. The rocker arm setup is operated by the camshaft lobe rubbing directly on the rocker. Stem to rocker clearance is maintained with a hydraulic valve lash adjuster for "zero" clearance. The overhead camshaft is also something that we think of as a relatively new development, but it's not. In 1898 the Wilkinson Motor Car Company introduced the same feature on a car.