Figure 3-40. - Crankshaft construction.

The crankshaft, with the exception of the bearing journals, is plated with alight coating of copper.

The bearing journals are case-hardened.

The bearing journals are ground to size.

Threads are cut into necessary bolt holes.

Crank throw arrangements for four-, six-, and eight- cylinder engines are shown in figure 3-41. The arrangements of throws determine the firing order of the engine. The position of the throws for each cylinder arrangement is paramount to the overall smoothness of operation. For the various engine configurations, typical throws are arranged as follows:

In-line four-cylinder engines have throws one and four offset 180 degrees from throws two and three.

V-type engines have two cylinders operating off each throw. The two end throws are on one plane offset 180 degrees apart. The two center throws are on another common plane, which is also 180 degrees apart. The two planes are offset 90 degrees from each other.

In-line six-cylinder engines have throws a-ranged on three planes. There are two throws on each plane that are in line with each other. The three planes are arranged 120 degrees apart.

V-type twelve-cylinder engines have throw arrangements like the in-line six-cylinder engine. The difference is that each throw accepts two-engine cylinders.

V-type six-cylinder engines have three throws at 120- degree intervals. Each throw accepts two- engine cylinders.

The crankshaft is supported in the crankcase and rotates in the main bearings (fig. 3-42). The connecting rods are supported on the crankshaft by the rod bearings. Crankshaft bearings are made as precision inserts that consist of a hard shell of steel or bronze with a thin lining of antifrictional metal or bearing alloy. Bearings must be able to support the crankshaft rotation and deliver power stroke thrust under the most adverse conditions.

The crankshaft rotates in the MAIN BEARINGS located at both ends of the crankshaft and at certain intermediate points. The upper halves of the bearing fit right into the crankcase and the lower halves fit into the caps that hold the crankshaft in place (fig. 3-43). These bearings often are channeled for oil distribution and may be lubricated with crankcase oil by pressure through drilled passages or by splash. Some main bearings have an integral thrust face that eliminates crankshaft end play. To prevent the loss of oil, place the seals at both ends of the crankshaft where it extends through the crankcase. When main bearings are replaced, tighten the bearing cap to the proper tension with a torque wrench and lock them in place with a cotter pin or safety wire after they are in place.

VIBRATION DUE TO IMBALANCE is an inherent problem with a crankshaft that is made with