What is plastigauge used for?

Plastigauge is a specialized tool used to measure the clearance between engine components, particularly in the context of main bearings. It is a plastic thread that you place between the bearing and the journal of the crankshaft. Once the assembly is tightened to specifications, the plastigauge squishes and provides a measurable width that corresponds to the gap between the two surfaces. This measurement allows mechanics to ensure that the clearance is within the manufacturer's specified range, which is crucial for the correct operation of the engine. Proper clearance is essential to avoid excessive wear, overheating, or potential engine failure due to improper lubrication. This makes plastigauge particularly valuable during engine rebuilds or when replacing bearings, ensuring that everything is properly aligned and fitted.