If the S55 engine has a weak point, it is the crank hub. BMW have been using this design for years and it has served us well. However, the S55 is a different animal. It revs higher, runs more boost and puts down more power than a tuned N54. Since the crank hub isn'y keyed, it can tend to slip under extreme load, at high revs, or pretty much whenever else it feels like it.
The actual causes are not known. Speculation runs rampant, however; we do know that DCT, Manual, bone-stock, or heavily modified engines all run the same chances of failure. This crank hub from Gintani hopes to remedy that problem.
Consisting of a Gintani F8X One Piece Crank Hub, Installation Crank Bolt, Key Hole Drill Bit, Key Hole Drill Block, and Gintani Upgraded Crank Bolt. Everything you need to lock that sucker down and ensure that your S55 won't turn into a fancy paperweight.
"But I don't race or modify my M-car".
Well, that's fine and probably a good way to keep your cost of ownership down. It's also irrelevant. Simply leaving the stock hub alone is an extreme gamble with insultingly expensive consequences. Similar in practice to not wearing a seatbelt or not looking both ways before you cross the street. You MIGHT be fine...then again if it all goes sideways you're SOL. The price of a replacement S55 is just short of $10,000 so the question you have to ask yourself is, Do you feel lucky? Well, do ya?
A small price to pay for a big piece of mind.