BEAUTIFUL VIEW

Structure and material

Multi-cylinder engines for cars and motorcycles use assembled con-rods like that shown in Fig. 9.16. The big end consists of two parts. The bottom part is called the bearing cap, and this is bolted to the con-rod body. Honing finishes the assembled big end boss to an accurate circular shape. The mating planes of the cap and rod body should be finished accurately in advance because this influences the accuracy of the boss. The plain bearing is sandwiched between the crankpin and big end.

Hot forging shapes the assembled con-rod. Cr-Mo steel JIS-SCM435 or carbon steel JIS-S55C are generally used. Free-cutting steels are frequently used when high machinability is required. Toughening is a typical heat treatment for carbon steel. The recent tendency to pursue high strength at reduced weight has led to the use of carburized SCM420 as well, which is very effective if the con-rod is designed to receive high bending loads.

The science and technology of materials in
automotive engines
Hiroshi Yamagata
Woodhead Publishing and Maney Publishing
on behalf of
The Institute of Materials, Minerals & Mining
CRC Press
Boca Raton Boston New York Washington, DC
WOODHEAD PUBLISHING LIMITED
Cambridge England

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