Crankcase, Crankshaft, Main Bearings & Flywheel

A.DESCRIPTION :

The engine block is the main body of the engine, around which the engine is built. It is a one piece casting and webs integral with it form the upper halves of the main bearing supports. The lower half bearing supports are in the form of caps machined to mate with the webs in the crankcase. On the upper face of the crankcase are replaceable heli-coil thread inserts for the cylinder head capscrews. These inserts are manufactured from stainless steel which will not rust or corrode. Through accuracy in manufacture, frictional loss between the capscrew thread and the insert is reduced, resulting in an increased clamping pressure on the cylinder head gasket for a given torque on the bolts.

The crankshaft is supported in 5 main bearings for 4 cylinder engine with end thrust on the rear and for 3 cylinder engine it is supported in 4 main bearings. The bearings are of the steel backed insert type and do not require fitting on assembly. The bearing caps, which hold the lower bearing inserts in position, are not interchangeable and each one is stamped with its location in the crankcase No.1 is at the front. The caps are secured to the crankcase by capscrews and lockwires in early models and by “Place” bolts, which do not require any locking mechanisms, in later models.

During manufacture main bearing caps are rough machined, then assembled to the crankcase prior to being line reamed. This results in each bearing cap being fitted for only one position, therefore, finished bearing caps cannot be supplied individually for service due to the necessity for line reaming to fit the particular bore where it is intended to mate.

The crankshaft supports the connecting rods and pistons along its length and converts the reciprocating movement of the pistons into the rotary movement required to drive the transmission. At the front end of the crankshaft is the gear which drives the timing gear train and the pulley which drives the fan and water pump. The flywheel is mounted on the rear of the crankshaft and to this is mounted the clutch which forms the link between the engine and transmission. The purpose of the flywheel is to oppose and moderate, by its inertia, any fluctuation in the speed of the engine. It counteracts varying torques during the stroke of the engine and provides a rotating balance weight which carries the crankshaft over dead centres. The flywheel is secured to the crankshaft by six capscrews with locking plates. Dowels are provided in the crankshaft flange for accurate location. The starting ring gear is a shrink fit on the flywheel and is replaceable.

Extreme care must be taken to assure perfect cleanliness of the crankcase, crankshaft and bearings after service has been completed.