What is an Over Head Valve (OHV) engine?
In today's Power Equipment market you may see a machine advertised with an "Over Head Valve" or "OHV" engine. What does that mean? First of all, let's understand that there are 2 basic valve configurations in today's engine. These configurations are:
- L-Head (commonly referred to as "flathead", "conventional head", "valve in block" or "side valve"). As some of these names imply, the L-Head engine has the valves positioned in the block, typically next to the piston/cylinder.
- Over Head Valve (commonly referred to as OHV or "valve in head"). Again, as the name implies, the OHV engine has the valves positioned in the head of the engine, above the piston/cylinder. The valves are also in an inverted position when compared to the L-Head engine.
So how are the L-head and OHV engine different from each other? The L-head is the "old" design, with the valves in the block. The valves normally are positioned along side the cylinder with the tops of the valves being even with the top of the cylinder. Below is a diagram of a L Head or flathead engine, courtesy of howstuffworks.com.
The OHV engine, on the other hand, has the valves positioned in the head. The valves are positioned directly above the piston, as shown in the photo below.
Next time we will discuss the advantages of the OHV engine versus its L-Head engine counterpart.