When using Plastigage to check rod-bearing clearance, install rod bearings onto the rod and rod cap. Install the rod onto the crank’s rod journal (make sure rods are in correct order) with fillet chamfer sides facing journal fillets. Following the procedure we’ve already discussed, lay a piece of Plastigage onto the exposed rod journal, install the rod cap and tighten, then remove the cap and measure the Plastigage. Again-and we need to stress this point-do not allow the crankshaft to rotate when Plastigage is in place. The crank must remain stationary.
Next, measure the crankshaft journal (for that specific bearing location) with a micrometer. Subtract the journal diameter from the installed bearing ID to determine bearing oil clearance. A good rule of thumb dictates that you should have about .001 inch of clearance per inch of shaft diameter. For instance, if a main journal outer diameter measures 2.375 inches, then you should have about .0024-inch clearance. In order to provide a slight margin of safety (especially for rod bearing locations), you can add an additional .0005-inch clearance.
The V-series rod bearings typically feature a low to medium eccentricity and provides a hardened steel back. For applications involving crankshafts with large fillets, narrowed bearings are available (under a VN suffix) to accommodate increased crankshaft fillet clearance. The primary difference between the V-series and other Clevite 77 TriMetal bearings is the use of a lead-indium overlay. A lead indium overlay offers a slightly better conformability than a lead/tin/copper overlay, along with slightly reduced wear resistance.
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.