The 4 stroke engine powers most of the classic motorcycles over 250 cc. There are three designs of valve layout available for 4 stroke engines: over head valves (OHV) operated by push-rods (G), overhead camshaft (OHC) either gear or chain driven (F), and side valves (SV) operating directly on the camshaft (F). But what are the differences between the three designs?
The most common valve operating design up until the '70s was the OHV operated by push rods. The camshaft on this design is located in the crank cases or lower part of the cylinder block.
OHC:In the over head cam design, a camshaft is carried in the cylinder head. Some designs have both an inlet and an exhaust camshaft (commonly known as DOHC, or double overhead cam).
Side valve 4 strokes have their valves (B & H) mounted in the cylinder. This design was popular for many inexpensive, low performance engines.