OVER HEAD VALVE (OHV) ENGINE

OHV means OverHead Valve - an engine design where the camshaft is installed inside the engine block and valves are operated through lifters, pushrods and rocker arms (an OHV engine also known as "Pushrod" engine). Although an OHV design is a bit outdated, it has been successfully used for decades. An OHV engine is very simple, has more compact size and proven to be durable.
Downside: it's difficult to precisely control the valve timing at high rpm due to higher inertia caused by larger amount of valve train components (lifter-pushrod-rocker arm). Also it's very difficult to install more than 2 valves per cylinder or implement some latest technologies such as Variable Valve Timing - something that could be easily done in a DOHC engine.