If do not know those who receive exhaust valve to leave,obstruct point of view, also can use undermentioned method to try to decide. Rotational crankshaft when gear, make the first crock of piston is located in top dead centre (exhaust journey top dead centre or compress journey top dead centre) the position, next crankshaft when gear gets off, rotational camshaft when gear, make the first crock into exhaust cam acme up or downward, two cam contour line keeps horizontal, become " on character 8 " or " next character 8 " appearance, in crankshaft of this position mount when gear can assure to assemble the position correctly.