2582275 - 1024A CRANKSHAFT

Made from spheroidal graphite cast iron, induction hardened. It rests on five main bearings with bearing shells graded into different sizes.The crankshaft endfloat is optimized by two thrust washers located in relation to the centre main bearing.Eight counterweights arranged at 180° ensure that the crankshaft rotating masses are perfectly balanced. A channel runs along the inside of the shaft to lubricate the main bearings and big end bearings.

The crankshaft consists of:

  • main journals (1), which rotated in the main bearings with bearing shells interposed;
  • crank pins (2), over which the connecting rod big ends fit;
  • crank arms (3), the same height as half the travel, which connect the main journals to the crank pins.
The shaft is also prepared for:- the fitting of the flywheel; - the fitting of the sprocket which, via a toothed belt, transmits motion to the timing system components.The crankshaft is the component which, via the connecting rod, transforms the reciprocating rectilinear motion of the piston into a rotary motion.It is subjected to forces which vary dramatically in terms of intensity and direction, and must therefore be sufficiently strong.

Its shape is designed according to the:

  • number of cylinders
  • type of engine (in line, a v, a w, etc.)
  • number of main bearings
  • number of strokes (2 stroke or 4 stroke)

In order to prevent damaging engine vibrations, the crankshaft should be both statically and dynamically balanced. These vibrations are due to:

  • centrifugal forces, generated by the masses with rotary motion (crank pins, big ends, 1/3 of the weight of the connecting rod, crank arms);
  • inertia forces, generated by the masses with reciprocating rectilinear motion (piston, gudgeon pin, 2/3 of the weight of the connecting rod).
A shaft is said to be statically balanced when, resting on two supports, it remains balanced irrespective of the rotation position.A shaft is said to be dynamically balanced when, supported between two points corresponding to the rotation axis and made to rotate, it transmits a reaction equal to half of its own weight to each support.The addition of counter-weights in suitable positions balances the shaft either statically or dynamically.However, to lessen the engine vibrations, it is not sufficient to balance the crankshaft, but it is necessary also to ensure that its motion is uniform, by both offsetting the working cycles (following a given firing order) and by fitting the shaft with a suitable flywheel.The firing order is obtained by offsetting the cranks, in engines with several cylinders, at an angle equal to:α = 180° x t/i

where:

  • t = engine strokes
  • i = number of cylinders
In our case (4 stroke engine with 4 cylinders)The crank offset angle is:a = 180°x4/4 = 180°The cranks are arranged on the same plane and in parallel in twos.
There may be two firing orders: 1, 2, 4, 3 or 1, 3, 4, 2; the most common firing order is 1, 3, 4, 1 as the centrifugal forces and inertia forces are more balanced.