Plastigage is available in four different sizes for checking vertical oil clearances on main and rod bearing locations. Each package features a handy measuring scale printed in both inches and millimeters. Strips are also color coded for easy size range identification.

Recommended bearing clearances have been determined as a result of extensive R&D by bearing makers and engine manufacturers. Optimal clearances for specific engines can be further refined after running and teardown/inspection (such as would be performed by professional race engine builders).

Also note: If your measured clearance is too tight, DO NOT attempt to polish the bearing running surface with any type of abrasive pad or paper. Bearing overlays are extremely soft and thin and can easily be damaged or even removed by abrasive media.

Engine Assembly Lubricant
Using a quality engine-assembly lubricant is a smart thing to do. Bearing assembly lube is specially formulated to protect the engine bearing and crank upon initial start-up. In addition to all the 1/2 shell bearings, both rods and mains, be sure to apply this lubricant to the thrust bearing faces as well. Before attempting to position the crankshaft in place, always check for cleanliness. Carefully wash the crankshaft in hot soapy water using a soft, clean brush. Rinse with clean water and blow dry with compressed air. Once the crankshaft is clean and dry, apply a thin film of clean engine oil to the journals. Even though engine assembly lube has been applied to the exposed bearing surfaces, it's still a good idea to lube the crankshaft as well before installing. Lube all main journals and rod journals, applying lube well into and beyond the fillet areas.

Carefully position the crankshaft into the main bore saddles, being careful to avoid nicking the crankshat journals. The mere weight of the crankshaft contacting an edge of a block's main bearing saddle can easily nick, gouge, or scratch a crankshaft journal, which can degrade oil flow around the journal or result in a scored bearing, leading to bearing failure.

Connected Adjustments
Choosing a main bearings is one thing, but what about the connecting rods? Many of us put the connecting rods in and hit it with a torque wrench, but is there a better, more accurate way? Even if using the best rod bolts available, measuring bolt stretch offers a much more accurate method of achieving ideal clamping loads as compared with the use of a torque wrench. To use the bolt-stretch method, fasteners must be through bolts (not cap screws) and have flat ground ends that permit accurate measurement of overall length.

To measure rod bolt stretch, first measure the total rod bolt length (from the head surface to the tip of the shank) in the bolt's relaxed state (when installed onto the rod but without the nut). Then measure the bolt again after the nut has been tightened. The difference in length indicates the amount of stretch the bolt experiences in its installed state. For the majority of production rod bolts, stretch should be in the .006-inch range. Check with the supplier to obtain the proper stretch versus load specification. If the stretch is less, the bolt is probably experiencing too much friction that is preventing the proper stretch (requiring lubricant on the threads). If stretch is excessive, the bolt may have been pulled beyond its yield point and is no longer serviceable.