The Ultimate Guide to Measuring Automotive Bearing Clearances

Measuring Automotive Bearing Clearances with Plastigauge

Application: Plastigauge is widely used in automotive maintenance to measure the clearance between a crankshaft journal and its plain bearing shells.

Step 1: Access the Bearings

Remove the engine sump cover to expose the big-end bearings and retaining set screws.
Clean away surplus oil around the area.

Step 2: Prepare the Bearing

Unscrew the retaining set screws and release the bearing shells.
Wipe the journal and bearing shell surface completely clean.

Apply:

A thin smear of grease to the journal.
A small amount of silicone release agent to the shell.

Step 3: Place Plastigauge

Cut a piece of Plastigauge to the correct length (across the journal).
Position it on the journal, using the grease to hold it in place.

Step 4: Reassemble and Tighten

Refit the bearing shell.
Tighten the retaining set screws to the manufacturer’s torque specification.
⚠️ Do not rotate the journal during this step.

Step 5: Measure the Clearance

Remove the bearing shell again.
The Plastigauge will now appear as a flattened stripe across the journal/bearing surface.
Compare the width of the stripe with the calibrated gauge card supplied with Plastigauge.
Read the corresponding bearing clearance value.

Step 6: Clean Up

Ideally, remove all traces of Plastigauge with a clean oily cloth or an industrial degreasing solvent.
Any residue left is oil soluble and generally harmless to lubricated metal surfaces.

✅ Tip: Proper clearance ensures correct lubrication and prevents bearing wear or seizure. Too much clearance reduces oil pressure, while too little clearance risks overheating and scuffing.