A connecting rod journal measures 2.730 inches and its specifications is 2.750 inches what size bearings should be installed?

• A. O/S - 0.020 (oversized)
• B. U/S - 0.010 (undersized)
• C. U/S - 0.020 (undersized)
• D. Standard size

Answer: (D)

This question tests how to choose bearing size from the crank journal measurement and the service tolerance. Bearings are available in standard, undersize, and oversize to achieve the correct clearance between the bearing bore and the crank journal. The standard size bearing bore is designed for a journal around 2.750 inches, with a typical tolerance of about ±0.020 inch. The measured journal is 2.730 inches, which sits at the lower limit of that tolerance, so it is still within spec. Therefore, the correct choice is to install standard-size bearings. If the journal were outside that tolerance, you would select undersize or oversize bearings to bring the clearance back into specification.