What readings indicate that a crankshaft should be replaced after straightness testing?

What readings indicate that a crankshaft should be replaced after straightness testing?

• A. Any minor bend is acceptable.
• B. A slight runout less than stated by manual.
• C. Readings outside manufacturer limits indicate replacement.
• D. Runout cannot be measured with standard tools.

Answer: (C)

When checking crankshaft straightness, you compare the measured runout to the engine maker’s specified service limits. If any reading is outside those limits, replacement is required. This is because exceeding the allowable deviation means the crank’s alignment is beyond what the engine can tolerate, leading to uneven bearing loads, poor oil film formation, vibrations, and potential failure. Within-spec runout can often be tolerated or addressed by reconditioning per the manufacturer’s guidance, but once the limit is exceeded, repair isn’t reliable. The other statements aren’t correct because even small bends aren’t automatically acceptable, a runout within the specified limit does not require replacement, and runout can be measured with standard tools like a dial indicator.

When checking crankshaft straightness, you compare the measured runout to the engine maker’s specified service limits. If any reading is outside those limits, replacement is required. This is because exceeding the allowable deviation means the crank’s alignment is beyond what the engine can tolerate, leading to uneven bearing loads, poor oil film formation, vibrations, and potential failure. Within-spec runout can often be tolerated or addressed by reconditioning per the manufacturer’s guidance, but once the limit is exceeded, repair isn’t reliable. The other statements aren’t correct because even small bends aren’t automatically acceptable, a runout within the specified limit does not require replacement, and runout can be measured with standard tools like a dial indicator.