How to use a micrometer to test the crankshaft runout？
Jul 11, 2025|
Testing crankshaft runout is an important step in determining if the crankshaft is bent or deformed, especially when overhauling an engine or replacing the crankshaft.
The following are the general steps for properly testing crankshaft runout.
✅1.Set up symmetrical supports:
The crankshaft is usually placed on two V-blocks, symmetrically supported on the main journals at both ends to ensure free rotation.
✅2.Install the dial indicator:
Use a magnetic stand or fixture to align the micrometer probe vertically to the measuring point:
Radial runout: The probe is placed on the side of any middle journal, rotate the crankshaft one circle, and record the maximum and minimum reading difference.
Axial runout: The probe is placed on the end face of the thrust flange, and the end face runout is measured by rotating.
✅3.Read the beat value:
Runout = maximum value – minimum value, usually measured in units of 0.001mm
📏Recommended standards (with reference to typical diesel/gasoline engines)
✅Radial runout (crankshaft bending): intermediate journal reading, total difference/2 as bending. The upper limit is usually ≤ 0.03mm, and the conventional standard is ≤ 0.05mm
✅End face axial runout: usually controlled within the range of ≤ 0.07–0.21mm
✅Cleaning and pre-tightening: All contact surfaces are clean, and the probe is pre-loaded ~1mm to avoid measurement errors.
✅Slow and even rotation: Manually rotate the crankshaft a full circle, observe the fluctuations, and avoid inertia.
✅Symmetrical support: Both ends are at the same level to ensure accurate measurement.
✅Multi-point measurement: It is recommended to test multiple journals, and pay attention to comparing the runout difference of adjacent journals to evaluate the coaxiality
