The short version
- The S55's crank hub isn't positively locked to the crankshaft. Under a big enough jolt of torque it can turn on the crank.
- We regularly see slipped hubs on manual and DCT cars, tuned and standard.
- There's no warning. It just goes, and a replacement engine runs towards £10,000.
- We fit the Insane Performance 4-pin, one-piece hub: from £2,049 including VAT, in two working days.
What the crank hub actually does
At the front of the S55's crankshaft sits a hub. It drives the timing chain, which turns the camshafts, and it carries the oil pump drive. In other words, it's the part that keeps the top of the engine in step with the bottom.
On most engines, a part like this is keyed or splined to the crank, so it physically can't turn. On the S55 it isn't positively locked in the same way. It's held in place mainly by the clamping force of the central bolt. Most of the time that's enough. The problem is the moments when it isn't.
Why it slips, and how often
If the crankshaft gets a sudden, sharp change in torque, the hub can turn slightly on the end of the crank. The situations most often linked with it are:
- Extra power and torque from a tune, especially with bigger turbos.
- Hard launches, or a missed or rushed gear change.
- Wheel hop, or sticky tyres suddenly gripping.
- Regular track use and running to the limiter.
It isn't only a tuned-car problem. We regularly see slipped hubs on both manual and DCT cars, tuned and untuned. There's an element of bad luck to it. Tuning or track use doesn't guarantee a failure, but it means the luck can run out sooner than you'd expect.
What happens if it slips
Because the hub drives the timing chain, if it turns on the crank, the camshafts are no longer timed correctly to the pistons. A small slip can leave the engine running badly with fault codes. A bigger one lets the valves hit the pistons, and at that point you're looking at a replacement engine, not a crank hub.
There's no warning beforehand. It isn't a part that wears gradually and starts making a noise; it just goes. Sourcing a good used engine and fitting it typically runs towards £10,000, depending on what the engine costs. That's why so many owners choose to fix the hub before anything happens.
How we fix it
The fix replaces the factory setup with an upgraded hub that is mechanically locked to the crankshaft, so it can't turn however hard the engine is used.
We fit the Insane Performance 4-pin, one-piece crank hub. We chose it after seeing other respected BMW performance specialists get good results with it, and having now fitted more than 100 ourselves, we're more than satisfied with it.
What it costs and how long it takes
Our crank hub upgrade is from £2,049 including VAT, and the price is the same for every S55 car: the F80 M3, F8x M4, M2 Competition and M2 CS. We need the car overnight, over two working days. Drop it off on a Monday morning and it's ready on Tuesday afternoon.
As with every job, it's photographed as it goes, and the old parts are kept for you to inspect. If you're considering rod bearings, it makes sense to do them at the same time, and that's usually when we do them on an S55.
Does your car need it?
In Rob's words: do your research and understand the risks. If the worry of the hub failing is stopping you enjoying the car, it's money well spent.
If you're planning to remap the car, it's worth reading tuning an S55 and the crank hub too.
Common questions
Which cars have the S55?
The F80 M3 (2014 to 2018), the F82 and F83 M4 (2014 to 2020), and the M2 Competition and M2 CS (2018 to 2021). The original 2016 to 2018 M2 uses the N55 instead.
Can I drive the car normally after the fix?
Yes. Once it's done, the hub is locked in place and the car drives exactly as before. You just don't have the worry any more.
Is there a recall or a BMW fix?
No. There's no recall and no updated factory part, and it isn't something a standard dealer service addresses.
