Stock E9X M3 S65 V8 crankshaft vs. nitride surface hardened crankshaft
Nitriding is a process by which a crankshaft is hardened with surface treatments. This is the first time BimmerBoost has seen the process applied to the S65 V8 crankshaft from the E9X M3 but this process is used frequently in the automotive world.
This nitride treated crankshaft (on the left) was brought to our attention by @Michael@GermanAutoWerks
and BimmerBoost member @The Convert
explains the process and result well:
Originally Posted by The Convert
Sounds like a good way to harden the crankshaft, right? Here's a slightly more technical explanation:
Hence we come to nitriding, which is favoured by most of the manufacturers of racing crankshafts, especially for single-piece machined items. Nitriding aims to diffuse nitrogen into the surface of specially alloyed steels, rich in elements which are strong nitride-formers, most especially Chromium, Molybdenum and occasionally Aluminium, Vanadium and Tungsten. There are two main types of nitride hardening processes, namely gas-nitriding and plasma nitriding. There are similarities in the two processes, although the methods are very different. Both take place at around 500°C (900°F) and both are relatively long processes, often taking tens of hours and, in some cases, well over 100 hours. The relatively low processing temperature compared to carburising means that distortion should be much less pronounced.
Essentially, quite a bit of heat is used on the surface during the process.
There are several different ways crankshafts are hardened including induction and tuftriding hardening. Nitriding offers certain advantages.
Nitrided crankshafts can easily be welded and ground without concern. A .010 undersize grind will cause some of the benefits of nitriding to be lost. At .030+ undersize, nearly all of the nitriding benefits are lost. Therefore, it is recommended to have the crankshaft hardened again after grinding.
Definitely something for those looking to strengthen their crank (supercharged cars for example) without buying an entirely new custom forged crankshaft.