One form of four-cycle reciprocating engine side valve (Sidevalve engine and the abbreviation are SV). A lot when written in Japanese, "Side valve type" in the main parameter table etc.Moreover, it is called, "F head" and "Flat head engine" from having shape with a flat cylinder head.
It is a mechanism old-fashioned ..in addition.. now at the time of the main current of the engine for the car and the motorcycle DOHC and SOHC. OHV of the push rod drive type that is becoming old-fashioned already (overhead valve)A big feature is to be arranged upward on the piston the exhaust of ..breathing in.. - valve, and queuing up next to the cylinder. It drives directly with the camshaft that this is arranged in the vicinity of the crank shaft.
Because the structure is very simple, the main body of the engine (especially, cylinder head) can be made compact, and driving in engine part is few, it becomes a strong engine. However, on the other hand, the surface area of the combustion chamber that cannot raise the compression ratio enough is large because the combustion chamber becomes a sideways long, wide shape, and the heat loss has the fault of the large generation of the backfire etc. easily.
Moreover, it is the maximum weak point that max power lowers by all means as a permissible rotational speed of the engine is limited to about 4,000 rpm or it or less because the flow of exhaust is very bad, and the time that hangs to the flame spread is long. The structure of the reciprocating engine came OHV and to evolve to OHC (overhead camshaft and SOHC→DOHC) furthermore to cancel these faults.
The organization for the car and the motorcycle is not approved any longer now, and the usage is limited to a general-purpose engine (example and Robin made in Fuji Heavy Industries engine "EY (gasoline)/EY-K (kerosene) series. " etc.) such as for the dynamo and the pump and for a part of management machine (part of "Ranee management machine" series made of Makita Numazu (old and Fuji Robin Industries)). However, taking the place in OHV and a senior model of SOHC is already current states in the main force in the general-purpose engine.
