The Difference Between OHV & L-Head Snowblower Engines

Small Engine

• Many snow blowers are powered by small gasoline engines. These engines are more simplified than the engines found in modern passenger vehicles and can be grouped into two categories -- overhead-valve and L-head. The main difference between overhead-valve and L-head engines is the cylinder head design and the way the valves operate. The lower end of the engine -- the pistons, connecting rods and crankshaft in both engines operate similarly.

Cylinder Head

• Most small engines used in snow blowers have a cylinder head. The head mounts to the top of the engine block and forms the top of the combustion chamber of the cylinder. The two main types of small engines used in snow blowers -- L-head and overhead-valve -- have completely different cylinder head designs. The cylinder head in an L-head engine contains no moving parts. Air-cooled L-head cylinder heads may have cooling fins cast into the exterior surface. The cylinder head in an overhead-valve engine contains the valves. Unlike the head in an L-head engine, the overhead-valve engine utilizes a valve cover to seal the engine oil, rocker arms, valve springs, and other parts from the elements.

L-Head Engine

• This type of engine contains the valves, valve guides, and valve springs within the engine block. The valves are usually located next to and parallel to the cylinder bore. The valve heads are facing upwards. The opposite end of the valve makes contact with lobes on the camshaft, causing the valves to open and close at the correct time. Many automotive engines prior to the 1960s used this type of engine, which was reliable and inexpensive to manufacture because it has less moving parts than an overhead-valve engine. The more simple design of the L-head unit leads to a combustion chamber that does not burn fuel as efficiently as an overhead-valve engine. This may cause the L-head engine to use more fuel and create more emissions than its overhead-valve counterpart. For this reason, some localities may forbid the sale of new snow blowers that use L-head engines.

OHV Engine

• The overhead-valve engine is used in most passenger vehicles built as of 2012, as well as many snow blowers. This engine design is more complex than the L-head design. The cylinder head on an OHV engine is more than just a metal plate to seal off the combustion chamber -- it contains the valves, valve guides, valve springs and rocker arms. The valve heads in an OHV engine face downward, as opposed to the L-head engine where they face upward. This type of design has a more efficient combustion chamber than an L-head engine that may lead to better fuel economy and less emissions. Lobes on the engine camshaft operate the pushrods, which cause the rocker arms mounted within the head to move up and down. This in turn opens and closes the valves. A disadvantage of an overhead-valve engine, as compared to an L-head engine, lies in the increased amount of moving parts involved to operate the engine.