Comprehensive S55 Pinned Crank Hub Installation Kit

The S55 engine has had documented cases where the crank hub has slipped which causes timing problems or in severe cases engine damage. What is the crank hub? Simply explained, the S55 engine doesn't have a traditional keyed crank snout for the oil pump or timing chain sprocket. Rather the crank hub along with the timing sprockets creates an interference fit locking timing in place. BMW chose this design for the S55 engine because the timing cover is part of the block casting and it makes assembling the engine much easier. Additionally, it cuts down on assembly times and makes setting engine timing much easier since all the timing components are free-floating until torqued to spec. The major downside to this design is the only thing keeping your engine mechanically in time is the torque from the crank center bolt. If this center bolt loses preload (torque) on the crank hub it will cause the main timing chain sprocket to slip causing the engine to go out of time or to skip timing altogether causing serious engine damage.

How common is this problem? It's hard to say. There are very high-mileage S55-powered BMW's out there that have never been opened and are just fine. There are very low mileage cars that had the crank hub slip with less than 10,000 miles. There is no guarantee that every S55 will experience this problem. But there is no guarantee that it won't happen either. Usage type, driving style, transmission type, horsepower level, etc are all potential factors that can influence the possibility of a spun crank hub.

If you're a new owner of an F8X S55-powered BMW or you have had yours since new you have to consider the options to address this potential problem. FCP Euro believes the best solution is a pinned two-piece crank hub for three reasons:

1) The pinned/keyed crank hub has no possibility of slippage even if the crank hub center bolt were to lose torque. It's mechanically locked to the crankshaft similar to how traditional crankshafts have timing sprockets keyed to the crankshaft.
2) The two-piece design still allows for easy assembly of the timing components just like the factory three-piece design
3) Fewer components: the two-piece keyed crank hub is as the name suggests, two pierces. These two pieces are keyed to one another (the oil pump sprocket pinned to the crankshaft and the timing chain sprocket/hub keyed to the pinned crank hub sprocket. As opposed to the factory setup which is three individual pieces that are friction fit when torqued to spec.

This kit includes all the gaskets, seals, and hardware required for installing Evolve's 4 pin two-piece crank hub. This kit includes all new timing guides, chains, tensioners, and other pieces needed for renewing the timing components during the installation of the pinned crank hub. A basic kit without new timing components is available and sold as p/n KIT-11237574827KT.