The S55 Crank Hub Problem
If you own an F80 M3, F82 M4, or F87 M2 Competition and you are planning any power modifications, this is the most important article you will read. The S55 crank hub issue is the single most discussed, most feared, and most preventable failure mode on the platform. Understanding it — and addressing it — should be step one in any S55 build.
What the Crank Hub Is
The crankshaft hub sits at the front of the crankshaft and drives the timing chain. The timing chain synchronizes the crankshaft (pistons) with the camshafts (valves). If they lose sync, valves open at the wrong time, pistons collide with valves, and the engine is destroyed.
On the S55, the crank hub is secured by a press-fit interface and a single center bolt — no mechanical key or pin. It relies entirely on friction and bolt clamping force to stay in position.
What Goes Wrong
Under high torque loads — particularly repeated, sustained loads from hard driving, track use, or increased boost — the center bolt can work loose. The crank hub spins relative to the crankshaft. This is called crank hub slip.
Even a few degrees of slip is catastrophic. The timing chain loses sync with the crankshaft. Pistons and valves occupy the same space at the same time. The result: bent valves, cracked pistons, damaged cylinder head, and a destroyed engine. Repair costs start at $15,000-25,000+, and in many cases the owner is looking at full engine replacement.
When Is It at Risk?
The crank hub failure has been documented on both stock and modified S55 engines. It is not exclusively a modified-car problem. However, risk increases significantly with:
- Increased power and torque — more force on the crankshaft means more force trying to spin the hub
- Higher boost levels — tuned cars see meaningfully higher cylinder pressures than stock
- Aggressive driving — track days, drag launches, and repeated hard acceleration cycles stress the press-fit interface
- Engine heat cycles — repeated heating and cooling can affect the interference fit over time
Most shops in the S55 community recommend addressing the crank hub above 500 whp. Some recommend it before any tune at all, especially for cars that will see track use.
The Fix
The fix: mechanically lock the crank hub to the crankshaft using a precision-machined keyway or pin. A hardened steel key is installed into slots machined in both the crankshaft and hub, physically preventing rotation. The bolt and press fit become secondary retention, not the sole retention.
The fix is permanent. Once pinned, this failure mode is eliminated entirely. No maintenance, no re-torquing, no ongoing concern. Companies like BMP Design offer proven solutions installed on thousands of S55 engines.
Cost and Timing
A standalone crank hub fix typically costs $2,000-4,000 depending on the shop and solution used. The smart move is to do it alongside another service that already requires front-end access — a clutch job, oil pan gasket, or turbo upgrade. Combining work saves significant labor cost.
When to do it:
- Before your first tune — if budget allows, this is the ideal time
- Before any turbo upgrade — non-negotiable at this power level
- Before any track day on a tuned car — sustained high-load driving is exactly the condition that triggers failure
- Proactively on any S55 you plan to keep long-term — even stock, the peace of mind is worth the cost
Not Every S55 Fails
It is important to be clear: many stock S55 engines run for 100,000+ miles with no crank hub issues. This is not a guaranteed failure. It is a known, documented failure mode with a catastrophic outcome. The probability is low on a stock, gently-driven car. But the severity is maximum — total engine loss.
The math is simple. A $2,500 preventive fix versus a $20,000+ engine rebuild. The community consensus is overwhelmingly clear: fix it before it fails.
AUTOLAB's Position
AUTOLAB strongly recommends the crank hub fix for any S55 customer planning modifications beyond a basic Stage 1 tune. We consider it a prerequisite for any serious build on this platform. If you are spending money on downpipes, turbos, or a built motor, the crank hub fix should already be done. It is the foundation that everything else depends on.
If you are buying a used F80/F82/F87 and the previous owner cannot verify the crank hub has been addressed, assume it has not. Factor the cost into your purchase decision. The S55 is an outstanding engine — the crank hub is its one significant design weakness, and it has a clean, permanent fix. Address it early and never think about it again.