Crankshafts & Components

The crankshaft turns the reciprocating motion of the pistons and connecting rods into the rotational motion that turns the transmission gears, axle shafts, and ultimately the wheels. The crankshaft turns on its axis in the cylinder block. The connecting rods are attached to offset crank throws, which enable the conversion of motion. Cast iron is commonly used to make low output engine crankshafts, while forged steel is needed for high horsepower motors.

Bearing journals are machined on the crankshaft so it can be supported in the cylinder block and to attach the big ends of the connecting rods to the crank throws. The crankshaft rotates in the block on plain bearings supported by a thin film of pressurized oil, and the rods are supported in the same manner on the crank throw rod journals. Most crankshafts have counterweights to offset the mass of the piston and rod assemblies and maintain engine balance.

A flywheel is mounted at the rear end of the crankshaft to smooth power flow, and provide a mounting surface for the clutch assembly. On vehicles with automatic transmission a flexplate is used in place of the flywheel to which the torque converter is attached. Both flywheels and flexplates have teeth around their circumference where the starter drive engages. A vibration damper, also called a harmonic balancer, is mounted on the front of the crankshaft to dampen the torsional distortion created in the crankshaft during engine operation. Accessory drive pulleys are usually attached to the vibration damper.

Crankshafts are stout, precision made components that with normal vehicle maintenance and use, should last the life of the vehicle. However, lax maintenance can result in dirt getting between the crank journals and bearings, or reduced oil flow, either of which can result in scored journals, increased clearance, metal-to-metal contact and engine knock. In such cases, the most economical repair with the least vehicle down time can usually be achieved with a crank kit, which includes a fully machined crankshaft and replacement bearings.

Oil leaks at the rear main seal are another common crankshaft malady. We have replacement seals and seal kits for all popular vehicles, but in cases of extreme wear the crankshaft seal contact surface can become grooved, making a replacement seal ineffective. However, there’s no need to completely replace the crankshaft if the sealing surface is marred. On our digital shelves you’ll find easy to install repair sleeves that are a press fit onto the crankshaft, creating a smooth surface for effective sealing and oil control.