Crankshaft Maintenance: A Comprehensive Guide for Optimal Engine Performance

Crankshaft maintenance is a critical aspect of engine maintenance that involves the inspection, measurement, and repair of the crankshaft to ensure optimal engine performance and longevity. This comprehensive guide will provide you with the necessary technical details and quantifiable data points to ensure your crankshaft is well-maintained and your engine is running at its best.

Crankshaft Inspection: Identifying Wear and Damage

Proper crankshaft inspection is the foundation of effective maintenance. Here’s what you need to know:

  1. Visual Inspection: Carefully examine the crankshaft for signs of wear, damage, or cracking. Look for discoloration, pitting, or grooves on the journal surfaces, as well as any visible cracks or deformities.
  2. Magnetic Particle Inspection (MPI): This non-destructive testing method can detect surface and subsurface defects in the crankshaft. The crankshaft is magnetized, and a magnetic particle solution is applied, revealing any flaws or cracks.
  3. Liquid Penetrant Inspection (LPI): This method is also used to detect surface-breaking defects. The crankshaft is coated with a penetrant liquid, which is then removed, leaving the penetrant in any cracks or flaws, making them visible.
  4. Frequency of Inspection: The number and frequency of inspections will depend on the engine’s operating conditions and the manufacturer’s recommendations. As a general guideline, inspect the crankshaft every 500 to 1,000 hours of operation, or as specified by the manufacturer.

Measurement of Crankshaft Runout

crankshaft maintenance

Crankshaft runout is the amount of deviation from a true circular path when the crankshaft is rotated. Excessive runout can lead to vibration, noise, and reduced engine performance. Here’s how to measure and evaluate crankshaft runout:

  1. Dial Indicator Measurement: Use a dial indicator to measure the runout at each main journal and pin journal. The indicator should be mounted on a stationary fixture and positioned to measure the radial movement of the crankshaft as it is rotated.
  2. Manufacturer’s Specifications: Refer to the engine manufacturer’s specifications for the maximum allowable crankshaft runout. Typical values range from 0.025 mm (0.001 in) to 0.125 mm (0.005 in), depending on the engine size and application.
  3. Corrective Actions: If the crankshaft runout exceeds the manufacturer’s specifications, the crankshaft may need to be reground or replaced to restore proper alignment and balance.

Crankshaft Grinding: Restoring Dimensions

If the crankshaft journals or bearings show signs of wear or damage, the crankshaft may need to be ground to restore its dimensions. Here’s what you need to know:

  1. Measurement of Wear: Use a micrometer to measure the diameter of the crankshaft journals and bearings. Compare the measurements to the manufacturer’s specifications to determine the amount of material that needs to be removed during grinding.
  2. Grinding Tolerances: The amount of material removed during grinding should be within the manufacturer’s specified tolerance. Typical tolerances range from 0.025 mm (0.001 in) to 0.125 mm (0.005 in), depending on the engine size and application.
  3. Surface Finish: After grinding, the crankshaft journal surfaces should have a smooth, uniform finish with a surface roughness (Ra) value of 0.2 to 0.4 micrometers (8 to 16 microinches), as specified by the manufacturer.
  4. Balancing: Following the grinding process, the crankshaft should be dynamically balanced to ensure even mass distribution and minimize vibrations.

Crankshaft Balancing: Ensuring Smooth Operation

Crankshaft balancing is the process of ensuring that the crankshaft’s mass is distributed evenly around its axis. This helps to minimize vibrations and ensure smooth engine operation. Here’s how to approach crankshaft balancing:

  1. Dynamic Balancing: Use a dynamic balancing machine to measure the crankshaft’s imbalance and determine the necessary counterweights or material removal to achieve proper balance.
  2. Manufacturer’s Specifications: Refer to the engine manufacturer’s specifications for the acceptable crankshaft balance tolerances. Typical values range from 2.5 g-cm (0.035 oz-in) to 10 g-cm (0.140 oz-in), depending on the engine size and application.
  3. Balancing Procedure: Follow the balancing machine’s instructions to add or remove material from the crankshaft counterweights until the desired balance is achieved.
  4. Verification: Recheck the crankshaft balance after any adjustments to ensure it meets the manufacturer’s specifications.

Crankshaft Replacement: When Repair is Not Enough

In some cases, the crankshaft may be beyond repair, and replacement may be necessary. Here’s what you need to know:

  1. Replacement Criteria: Factors that may necessitate crankshaft replacement include excessive wear, damage beyond the limits of grinding, or the inability to achieve proper balance.
  2. Replacement Costs: The cost of a replacement crankshaft can vary significantly depending on the engine type and the manufacturer’s specifications. Expect to pay anywhere from $500 to $5,000 or more for a high-performance engine crankshaft.
  3. Installation Procedure: Proper installation of the replacement crankshaft is crucial to ensure proper engine operation. Follow the manufacturer’s instructions for torque specifications, bearing clearances, and other critical installation parameters.

Technical Specifications and Guidelines

In addition to the measurable data points mentioned above, there are several technical specifications and guidelines that should be followed during crankshaft maintenance:

  1. MIL-STD-471: This military standard provides procedures and test methods for the verification, demonstration, and evaluation of qualitative and quantitative maintainability requirements for crankshafts.
  2. DOD-HDBK-791(AM): This defense handbook provides information on testing maintainability parameters, responsibilities for conducting the tests, and evaluation of the maintainability features of crankshafts.
  3. ISO 4156: This international standard specifies the performance requirements and test methods for crankshafts used in reciprocating internal combustion engines.

By following these technical specifications and guidelines, you can ensure that your crankshaft maintenance practices are in line with industry standards and best practices.


Crankshaft maintenance is a critical aspect of engine maintenance that requires a thorough understanding of the various measurable and quantifiable data points involved. By following the guidelines and best practices outlined in this comprehensive guide, you can ensure that your crankshaft is well-maintained, your engine is running at its best, and your investment in your vehicle is protected.

РMaintenance Performance Measurement and Management, Luleå University of Technology, 2012.
– Innovation for Maintenance Technology Improvements – GovInfo, 2013.
– DOD-HDBK-791 (AM) – AcqNotes, 2013.
– MIL-STD-471 – Military Standards, 2022.
– ISO 4156 – International Organization for Standardization, 2021.