What is Plastigage used to check?

• A. Bearing oil clearance
• B. Camshaft runout
• C. Piston ring end gap
• D. Valve lash

Answer: (A)

Plastigage measures the clearance between a bearing surface and the crankshaft journal. You place a thin Plastigage strip on the bearing surface, torque the cap to spec, and the strip compresses under the load of the bearing. After removing the cap, you compare the printed width of the deformed strip to the included scale to determine the oil clearance. This reading tells you whether the bearing clearance is within the engine’s specifications—too tight can cause contact and overheating, too loose can allow excessive oil flow and wear. Plastigage is commonly used for main and connecting-rod bearings. It isn’t used for camshaft runout, piston ring end gap, or valve lash, which are measured with different tools like dial indicators or feeler gauges.