3 Things Every BMW Modder Needs to Know About the S55 Crank Hub
BMW platforms are a favorite for enthusiasts who love to modify their vehicle and chase extra horsepower. If your build is based on the S55 engine, there is one part you cannot overlook: the factory S55 crank hub.
Once you start turning up the power and pushing the engine higher than stock capabilities, the stock hub can slip. In mild cases, this may result in timing issues and reduced performance. In more serious cases, it can lead to major engine damage. If you are planning to go beyond stock power, it is important to understand how this vital component works and when to upgrade it.
It Can Slip for Multiple Reasons
The BMW crank hub is known to slip when power and RPMs rise significantly above factory capabilities. As you add more horsepower, drive the car harder, and shift more aggressively, you are putting extra load on a design that wasn’t built to withstand those conditions.
Traditional crank hubs rely on pins and friction to keep the assembly from moving. Under stock power, that may be enough. Once you increase boost and run the engine harder, however, those pins can shear or lose their grip, which lets the hub rotate on the crankshaft. That’s when timing gets impacted and expensive problems can start to appear. If you plan to modify your S55, treating the crank hub as a must-upgrade item is a smart move.
Know When to Replace It
If you are adding power to your S55 engine without addressing the crank hub, you are taking on unnecessary risk. Hard street driving, frequent track use, or any build that aims for significantly more horsepower than stock can push the factory hub past its limits.
An upgraded BMW S55 crank hub should be on your list if:
- You plan to increase boost, switch turbos, or chase higher dyno numbers
- You regularly rev the engine to redline
- You enjoy performance driving or attend track days
Preventing crank hub slip is not just about performance. It’s also about protecting the engine from timing-related failures that can damage valves, pistons, and other internal components. If a proven upgrade can reduce that risk, it’s worth installing before problems arise.
Spline Lock vs. Pins: Which Is Best?
The stock S55 crank hub uses small pins, and those pins are the weak link once you start turning up the power. A better option is a hub made with spline lock technology. Instead of relying on pins, a spline lock design uses a series of precisely cut splines that press into the crank snout.
This design forms a full 360-degree mechanical connection between the crankshaft and the hub. There is no need for drilling, pinning, or welding. The hub is locked in place by its shape and fit rather than by small pins that can fail. A quality spline lock hub is also fully reversible, so you are not permanently altering the crank. For a serious S55 crank hub upgrade, that combination of strength, ease of installation, and serviceability makes spline lock the better choice.
Find a spline lock crank hub for your S55 engine from Vargas Turbocharger Technologies at vargasturbo.com