The present study investigates the dynamic response of single-cylinder reciprocating engines. In particular, simplified models of the crank-connecting rod mechanism are examined, which take into the flexibility of the crankshaft. Crankshaft, connecting rod and piston are major parts of the crank-connecting rod mechanism, and their size, mass, centroid location parameters are required precisely in manufacturing process. However, manufacturing error cannot be avoided completely in practical manufacturing process, and it would lead to different vibration performance of engine. Therefore, understanding the effect of manufacturing error on the vibration performance of engine is the aim of this paper. In order to obtain dynamic characteristics of engine, both rigid and flexible body dynamics simulation were done by using software ADAMS.