GB/T 726-94
Reciprocating internal combustion engines — Designations of the direction of rotation, valves in cylinders and cylinder heads, and definitions of right-hand and left-hand in-line engines and engine orientation
往复式内燃机旋转方向、气缸和气缸盖上气门的标志及直列式内燃机右机、左机和发动机方位的定义