What tool can be used to determine the main bearing clearances in a propulsion diesel engine?

The depth micrometer/plastigage is an appropriate tool for determining the main bearing clearances in a propulsion diesel engine. This tool provides an accurate measurement of the space between the main bearing and the crankshaft. Plastigage involves inserting a plastic gauge strip between the bearing surfaces and then tightening the assembly. Afterward, the width of the flattened plastigage indicates the gap size, which corresponds to the bearing clearance. This method is widely used because it allows for easy and precise measurement in confined spaces typical of engine compartments.

The other tools listed serve different purposes. A dial indicator is primarily used for measuring linear distances or the runout of rotating parts but is not suitable for measuring bearing clearances directly. A caliper gauge can measure dimensions but lacks the specificity needed for assessing clearances accurately in this context. Lastly, a torque wrench is used to apply a specific amount of torque to fasteners but does not measure clearances. Therefore, the depth micrometer/plastigage stands out as the most suitable and specialized tool for this task.