While the main purpose of a crank is obvious, it has many other demands placed upon it. Rotating constantly as it does, it is ideal for taking drives to other assemblies such as pumps. While it is possible to drive pumps electrically - and there are some advantages to doing this - it is banned in some forms of motorsport, and the vast majority of series-production engines drive their pumps mechanically.
With very few exceptions, four-stroke engines use camshafts to open poppet valves, and the cams need to be driven at a fixed speed ratio to the crankshaft, and timed to the motion of the piston very precisely. While it would perhaps be convenient to do so, nobody drives the cams electrically, and so a mechanical connection between the crankshaft and the camshaft(s) is necessary. Read more…
The fatigue behaviour of a crankshaft is dictated by the service loads it is expected to cope with, its manufacture and its geometry. In numerous articles concerning crankshafts, surface treatments and materials, RET-Monitor has stressed the critical importance of compressive residual stresses for increasing fatigue life, and it is here that the correct selection of material, heat treatment and further processing is of utmost importance. 
The previous article looked at the recent trend in crankshaft lubrication commonly known as the ‘nose-feed’ method. In that article, the basics of the concept were explained, along with some of the perceived advantages of using this method of providing lubrication to the connecting rod big ends and possibly the crankshaft main bearings too.
In a previous article discussing the oil holes which are necessary in crankshafts, the author briefly discussed one of the methods by which oil is transferred to the crankpins for the purpose of lubricating the big end of the con rod and its bearings. The article discussed how the oil, having arrived at the main bearing, must make its way through the crankshaft via the oil drillings to the crankpin. We touched briefly on compound-angle drillings and axial drillings in that article, but didn’t mention a method of crankpin oiling which has been 
In the author’s article on the mitigation of stress concentration in critical areas of crankshafts last month (Crankshafts: Stress-concentration mitigation), we mentioned the 1943 paper by Matinaglia. Some of his findings are repeated in the books by C.F. Taylor, which, if you don’t have a copy of these, you would do well to avail yourself of. The paper by Matinaglia is worth reading but, having been published many decades ago in a trade journal, is not easy to get sight of.
In previous articles on the subject of 
In previous articles on the subject of crankshaft materials and hardening, we have made reference to the benefits of having residual compressive stress at the surface of the component. With the nitride hardening treatment used extensively on crankshafts, we not only make the crankshaft more wear resistant, but the change to the composition of the surface also imparts compressive residual stress. There are other methods of achieving this other than by nitriding the crankshaft, and we shall begin to look at these after examining a simple case to show the benefits of residual compressive stress. 
We should all be very familiar with the primary functions of a crankshaft, namely as part of the mechanism which converts reciprocating motion into rotary motion, and to transmit torque to the outside world, where it might drive a gearbox, a generator or other piece of equipment. What a great many crankshaft designs also do is to provide lubrication channels which allow the passage of oil to the big end bearings, and possibly thereafter to the small end of the connecting rod.
In the design of crankshafts we have to incorporate counterweighting for various reasons, either for reduction of bearing loads, or to reduce or eliminate primary couples.
In the previous article, we looked at the hardening and tempering of crankshafts. This month we shall look at the final and probably most important stage of heat-treatment, namely that of surface treatments, especially nitride hardening, more commonly known as ‘nitriding’. Nitriding is essentially a surface treatment, and its effect extends to a finite distance below the surface of the component.
