Measuring Clearance in Engine Bearings With Plastigage

Plastigage is a simple and cost-effective method for measuring the clearance (separation) between fitted or hidden surfaces in engine bearings, Here's how it works.

  1. Prepare the surfaces:
    First, separate the surfaces between which you want to measure the clearance
    - Ensure that the surfaces are clean before using Plastigage.
  2. Apply Plastigage:
    - Cut a piece of Plastigage to fit across the bearing journal (the contact surface).
     - Place the Plastigage on top of the journal.
  3. Torque Down:
    - Install the bearing cap (or rod cap) and torque it down to the specified value and angle.
    - The Plastigage will be compressed between the bearing and the journal.
  4. Check Clearance:
    - Remove the bearing cap and compare the flattened Plastigage with the scale on the Plastigage packaging.
    - The width of the flattened Plastigage corresponds to the clearance.
    - Use the calibrated scale to determine the actual clearance. You can interpolate between scale marks for greater accuracy.
  5. Repeat for Other Bearings:
    - Repeat the process for other bearings in the engine.

Advantage of Plastigage: 

  • Inexpensive compared to bore micrometers.
  • Useful for measuring clearances in split bearings or where feeler gauges cannot be inserted.

Remember to follow the specific procedures for your engine and refer to the manufacturer's specifications.

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