Originally Posted by
Roelof
DLC is used for 2 reasons:
1) surface hardening
2) low friction surface to deal with the issue where lubrication stops working.
Lubrication is an issue with high rpm engines like the onroad engines. Lubrication has a speed limint to where it works. Going beyond lts say 45.000rpm with onroad engines there is a short moment of a bad lubrication, the low friction DLC surface will take care. All depends the qualuity of the used oil.....
Basically only the crankpin is most needed to have the DLC, that the whole crankshaft is done is just the process.
There is other ways to reduce the friction as well, some is used before they apply the DLC or it would turn in to a file.
But the hardness and low coefficient of friction does help if the oil or additives isn't there. I guess one reason why it has become more popular is all the full synthetic fuels for racing.
Piston pin can also benefit from it, but I don't think there is any engines anymore that run that.