The cylinder case is made of one piece cast iron comprised of a special alloy containing carbon, silicon, and chromium. This mixture provides good elasticity, and thermal expansion. The 6.2L is designed to match fit the cylinder bore with the piston. This is done by dividing the total diameter tolerance size range of 100.987-101.065 mm (3.975-3.979) into 6 size ranges. Each of the bore sizes is identified by a code letter A-B-C-D-E-G. This identification is metal stamped on the cylinder case pan rail adjacent to the proper cylinder, “A” size pistons for “A” size cylinder bores etc., by using this select fit method, the clearance is controlled to .089-.138mm (.0035 in.-.005 in.). See Figure 2-2.
There are 5 main bearings numbering 1 through 5 from the front of the engine. There is an arrow on the cap which points toward the front of the engine.
Each main bearing cap is retained with 4 bolts in order to provide a more rigid support for the crankshaft and minimize stress. The caps are made of nodular cast iron, and are torque driven in place on the machine line before boring, just the same as they are finally torque driven at assembly.
The center or number 3 bearing is the thrust bearing.
The main bearings are select-fitted to each of the 5 main bearing bores. The proper size code is stamped on the pan rail at the corresponding main bearing bulk head. The total diameter size range of the main bearing bores #1 through 5 is 79.826 – 79.850mm. The spread of .024mm (.0096″) is divided into 3 sizes. It will be stamped 1-2 or 3 on the pan rail. Each of the sizes is matched to the corresponding size of split bearing insert in the case half only. The split bearing insert for the main cap is match fitted to the crankshaft main journal.
Figure 2-3 shows the plant chart for main bearing installation. This matches the main bearing journal diameter with the case bore to come up with the proper size inserts.
These numbers 1, 2 & 3 are primarily for plant use in selecting the inserts of the standard, ,013mm (.0005 in.) U.S., and ,026mm (.001 in.) U.S.
These three bearings will be used in the field to obtain proper clearance on a crankshaft.
Service will continue to selectively fit bearing halves in the field by using plastigage, trying to obtain a clearance of .045-.083mm (.0018-.0032 in.) on #’s 1 thru 4, and .055-.093mm (.002-.0036 in.) on #5. The standard, .013mm (.0005 in.) U.S. and .026mm (.001 in.) U.S., bearings are for dealer service in selecting those clearances.