The crankshaftThe Crankshaft transmits the force transmitted to the connecting rod by the linear movement of the piston as torque to the flywheel of the clutch. The Crankshaft of a combustion engine converts the linear up and down movement of the piston in the cylinder into a rotary movement and forwards this via the primary drive to the clutch and the transmission. In almost all multi-cylinder engines, the individual lifting pins are offset from one another. The only exceptions are genuine V-engines, in which both connecting rods are mounted on a single pin.
Tasks of the crankshaft- absorb the piston forces
- generate a torque from the connecting rod force
- transmit the major part of the torque to the flywheel and clutch
- with the smaller part drive camshaft, oil pump generator, engine cooling and valve control etc.
Structure of the crankshaftEach Crankshaft has the shaft journals in one axis for the bearings in the crankcase and the crank journals for the conrod bearings. Shaft journal and crank journal are connected by crank webs. Crank pins and crank webs result in an uneven mass distribution, which is compensated by counterweights on the opposite side. One of the shaft journals is equipped with lateral thrust surfaces. The guide bearing for axial fixing of the crankshaft is mounted on this. It prevents, for example, displacement when the clutch is actuated. The pins of the crank shaft are hardened and ground in the surface layer. The Crankshaft must be dynamically balanced, accumulations of material can be eliminated by balancing holes. On the output side of the Crankshaft the flywheel is mounted on which the clutch is usually mounted. On the opposite side there is a gear wheel, chain wheel or toothed belt wheel and, if necessary, a vibration damper.
stresses on the crankshaft- high acceleration forces due to acceleration and deceleration of pistons and connecting rods
- on twisting and bending due to high centrifugal forces
- at the bearing points for wear
Nowadays motorcycles crankshafts are produced in two ways:
- Assembly of several prefabricated parts in which lifting and crank pins are pressed into the crank webs under high forces
- Forging, in which the blank is die-forged in one piece
A crankshaft is usually forged from alloyed quenched and tempered steel (nitriding steel) in a die and has a high strength. Crankshafts made of Cast iron with spheroidal graphite, on the other hand, has good vibration damping properties. There are also the so-called full cheek crankshafts for tuning purposes. With the use of Crankshafts the pre-compression in the crankcase can be increased, which leads to a considerably better filling level. The power speed shifts to the upper range. Both torque and power increase due to the increased flywheel mass of the all-metal version. Auﬂerdem also exist the crankshafts produced by the Taiwanese manufacturer Naraku, which offer the same advantages, nevertheless their weight is lower.