When checking main bearing clearance with plastigauge, what does a flattening plastigauge more at one end indicate?

When checking main bearing clearance with plastigauge, what does a flattening plastigauge more at one end indicate?

• A. The rod is bent
• B. The crank journal is tapered
• C. The crankshaft is bent
• D. The main bearing is over torqued

Answer: (A)

When using plastigauge to check main bearing clearance, a flattening of the plastigauge more at one end indicates an inconsistency in the shape or alignment of the components being measured. This uneven flattening typically suggests that the rod is bent. A bent rod would cause uneven pressure across the bearing surface as the rod does not sit evenly against the crankshaft, leading to more plastigauge compression at one end compared to the other. This scenario is important to identify because it can result in premature wear or failure of the engine components. The other factors mentioned do not directly result in asymmetrical flattening. For instance, a tapered crank journal would affect the overall clearance uniformly across the bearing rather than creating a significant difference from end to end, while a bent crankshaft would likewise cause uniform issues across the bearing surface. Over-torquing the main bearing could also lead to clearance problems but typically would not result in a distinctly more flattened plastigauge at one end unless it evolved from an underlying misalignment or bending issue.

When using plastigauge to check main bearing clearance, a flattening of the plastigauge more at one end indicates an inconsistency in the shape or alignment of the components being measured. This uneven flattening typically suggests that the rod is bent.

A bent rod would cause uneven pressure across the bearing surface as the rod does not sit evenly against the crankshaft, leading to more plastigauge compression at one end compared to the other. This scenario is important to identify because it can result in premature wear or failure of the engine components.

The other factors mentioned do not directly result in asymmetrical flattening. For instance, a tapered crank journal would affect the overall clearance uniformly across the bearing rather than creating a significant difference from end to end, while a bent crankshaft would likewise cause uniform issues across the bearing surface. Over-torquing the main bearing could also lead to clearance problems but typically would not result in a distinctly more flattened plastigauge at one end unless it evolved from an underlying misalignment or bending issue.