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Crankshaft (machining)

V2-90°-crankshaft blank with center bearing

Shown above is a blank for a two-cylinder V-engine. The center bearing, which can by no means be taken for granted in this type of engine, can be clearly seen. Apparently, the angle between the two cyllinders is 90°. Thereby can the ignitions be evenly distributed over one working cycle. The cylinders are not exactly opposite to each other. They are offset by the throw of the crank and by the width of the main bearing.

Materials used for crankshafts
Cast iron with nodular graphite (GGG)Low
Forged crankshafts without further finishing, which were forged after being more/less cooled down in certain temperature ranges.Medium
Relatively small amounts of alloying elements:
Chrome, Nickel, Manganese, Molybdenum, Silicon and/or Vanadium

Surface finishing reduces the danger of cracking

The forged crankshafts are often said to have a higher firmness due to the uninterrupted direction of the grain. Although this is basically correct, crankshaft damage generally begins with damage to the surface. Therefore, the specific shaping and finishing of the surface is often even more important. In order to protect the surfaces against permanent endurance-strain and to raise the contortion strength and hardness of the crankshaft, fringe layers and especially the running surfaces are induction hardened or treated with nitrite. The design of the crankshaft, in areas of higher tension with the danger of cracking, is crucial. For example, potential danger zones are the rounded off cross-over points from the bearing to the crank web, and the correct arrangement and treatment of the oil drillings.

Small series turned from one piece of material

This kind of treatment is especially important, also for crankshafts which have been turned in one piece. This process is common in small series production, e.g., in the Formula 1 or for rare veteran cars. Thereby, the blank made from a suitable steel alloy, must have a sufficient diameter. It is cut to length and receives plugs for clamping. The main- and big-end bearings are first roughly machined, then later given the finishing touches. The particular shape of the crank webs and counter-balances develops during the milling. The ensuing manufacturing process is, in principle, the same as the mass production manufacturing process. Only the hardening is different. Using modern casting technology, it is possible, with the appropriate amount of effort, to re-build a complete veteran car engine, and with suitable metalworking experience, even the whole car, this has already been done, e.g., with an Auto Union Type C.

More than 1 mm of material can be applied

The process of applying material directly to the worn out bearings is almost more universal. The beginnings of what is applied when cylinders are manufactured is, in principle, possible for all shafts. In this case, after removing the nitrite layer and after the suitable preparation through flame-spraying, a more than 1 millimeter thick layer of metal with a high molybdenum content is applied. This way, even the undersize bearing is possibly avoided. Should the normal bearing itself no longer be available, one can work in the direction of installing another one which is still being sold. In some cases, this method may even be cheaper than buying a new part. 06/07