1. The assembled crankshaft consists of several parts. A forging machine with a small capacity can forge these parts, resulting in lower costs than for the monolithic crankshaft, along with lower machining costs.
2. Without a retainer, the rollers of a needle bearing are likely to cause abnormal motion called skew, which leads to seizure or abnormal wear. The retainer maintains the intervals between the rollers to avoid this motion. Also, the roller does not have a perfect cylindrical shape but has a barrel shape, which prevents skew. The needle roller rolls with slip. The shaking of a crankpin and con-rod increases the slip. With sufficient lubricating oil, a plain bearing is suitable and costs less. Despite the low friction loss at the big end, no car engine presently uses a needle roller bearing for the big end.
3. Junkatsu Handbook,1987
4. The small roller bearings have been improved by the development of high-power motorcycle engines. Okuse H., et al.: SETC Technical Paper 911279.
5. Tekkouzairyouwoikasu Netsushori;Koyanagi,1982