How should crankshaft main bearing journals be measured?

Measuring crankshaft main bearing journals is a critical task in ensuring the proper functioning of an engine. Using an outside micrometer is the preferred method for this measurement because it provides a high level of accuracy and precision. An outside micrometer is designed to measure the outside diameter of an object with a resolution down to 0.001 inches (or 0.01 mm), making it ideal for measuring the journal diameters which must be within tight tolerances for optimal performance.

In contrast, other tools mentioned do not offer the same level of accuracy required for this specific measurement. A dial gauge is typically used for checking runout or alignment rather than direct measurements of diameters. A ruler lacks the precision necessary for measuring small tolerances, while a digital caliper, although more accurate than a ruler, may not always provide the same level of precise measurement as an outside micrometer in this context.

Thus, for the precise measurement of crankshaft main bearing journals, an outside micrometer is the most suitable choice, ensuring that the measurements taken will help maintain the integrity and performance of the engine.