BMW F80 Crank Hub Problem Explained
It's the one thing every F80 buyer hears about — and it's widely misunderstood. The S55's crank hub is a friction fit, not a keyed one, so under the extra torque of a tune it can slip on the crankshaft, upsetting the engine's timing. Here's exactly what it is, why it happens, and the pinning fix that solves it.
The crank hub sits on the front of the crankshaft and drives the engine's timing system. On the S55 (shared with the F8x M4 and the M2 Competition) it's held on by an interference fit — pressed tightly onto the crank and clamped by a central bolt, but with no key, spline or pin mechanically locking the two together. It relies purely on friction. At stock power that's usually fine; add the torque of a tune and that friction grip can be overwhelmed.
If the hub slips, timing goes with it
When the hub rotates relative to the crankshaft, the position the timing sensors think the engine is at no longer matches reality. Valve timing drifts out, the car may throw timing/correlation faults or run badly — and in a worst case the valves and pistons can meet, causing serious engine damage. It's not common on a careful stock car, but it's the reason this gets so much attention on tuned F80s.
Why It Happens
A stock-strength joint asked to hold tuned torque.
BMW designed the friction fit for the engine's factory output. The problem is that the S55 responds enormously to tuning — a simple flash can add big torque — and that extra twisting force is exactly what tries to rotate the hub against its press fit. Heat cycling, hard launches, high-rpm shifts and repeated big-torque hits all chip away at the grip. So while a slip can occur on a stock car, the risk climbs sharply once power goes up, which is why tuned cars are the focus.
What Actually Goes Wrong
From a small shift to a serious failure.
Warning Signs
Catch it early and it's a far smaller problem.
- Timing / camshaft-crankshaft correlation codes — the classic electronic flag that the hub has moved.
- Rough running or a check-engine light — as the timing drifts away from where the ECU expects it.
- A noticeable change after tuning — new fault codes or odd behaviour appearing soon after a power increase.
- Loss of power or a misfire — symptoms of timing that's no longer correct.
The Fix: Pinning
The accepted, durable solution is to pin the crank hub — drilling through the hub and into the crankshaft and inserting hardened dowel pins so the two are mechanically locked together and can no longer rely on friction alone. (Upgraded hub solutions exist too, but pinning the factory hub is the common route.) It's an involved job — the front of the engine has to come apart to access it — so it's most efficient to do before or alongside a tune, or as planned preventive insurance.
The smart approach
Most knowledgeable F80 owners treat pinning as essential before adding meaningful power — you pin first, then tune. On a car that's already tuned, having the hub pinned (with documentation) is one of the most valuable things you can find. If you're buying a tuned F80 without it, budget the job into your offer.
If You're Buying an F80
- Ask about the crank hub first — is it pinned, by whom, and is there documentation?
- Match it to the tune — a tuned car without a pinned hub is a real risk; price the job in.
- Scan for timing codes — check for any stored or pending correlation/timing faults.
- Review tune & track history — how much power, for how long, and how hard it's been driven.
- Pair with the full picture — read the S55 reliability guide for the rod bearings and the rest.
The Bottom Line for Owners
The crank hub isn't a reason to fear the F80 — it's a known, well-understood item with a proven fix. The rule is simple: pin before you tune, and buy a tuned car that's already been pinned (or budget for it). Treat any timing-related code seriously and address it promptly, and the S55 will reward you. See the full S55 reliability guide and the F80 hub.
FAQ
What is the crank hub problem?
The S55's crank hub is pressed onto the crankshaft with a friction fit and no key or pin locking it in place. Under the extra torque of a tune that grip can be overwhelmed, letting the hub slip on the crank and throwing the engine's timing out — which can run the car badly and, at worst, cause valve-to-piston damage.
Does it only affect tuned cars?
Tuned cars are by far the highest risk, because the added torque is what tries to rotate the hub. A slip can occur on a stock car but is far less common — which is why pinning is considered close to essential once power goes up.
What is "pinning" the crank hub?
Drilling through the hub into the crankshaft and inserting hardened dowel pins so the hub is mechanically locked to the crank, rather than relying on friction. It's the accepted durable fix, and it's most efficient to do before or alongside a tune.
What are the warning signs?
Timing or camshaft-to-crankshaft correlation fault codes are the classic flag, along with rough running, a check-engine light, or new odd behaviour appearing soon after a tune. Treat any of these as urgent on an S55.
Should I buy a tuned F80 that isn't pinned?
Be cautious. A tuned car without a pinned hub carries real risk, so either factor the cost of pinning into your offer or look for one that's already been done with documentation. A pinned, well-documented tuned F80 is the safer buy.
The Bottom Line
The F80 crank hub is a friction-fit weak point, not a ticking time bomb — understood and solved by pinning. The golden rule is to pin before adding power, and to buy a tuned car that's already pinned or budget for it. Respect timing-related codes, do the job properly, and the S55 is one of the great tunable M engines. Read the S55 reliability guide, and head back to the F80 hub.