The BMW S55 twin‑turbo straight‑six is a brilliant engine, but the crank hub is its single biggest weakness. This guide covers the symptoms, root causes, affected models, repair costs, and a clear verdict on whether to repair or replace.
BMW S55 crank hub failure is a known and potentially catastrophic weakness on the twin‑turbo straight‑six, where the crank hub slips on the crankshaft, causing timing to jump. It typically manifests as a sudden loss of power, engine warning lights, or complete engine failure. Repair costs can range from £3,000 to £8,000+ for a crank hub fix and timing reset, with full engine replacement potentially exceeding £12,000. Early diagnosis is essential to avoid a much larger bill.
For full symptom progression, affected models, and cost breakdown, read on.
S55 crank hub failures rarely happen without warning. The symptoms can be subtle at first, but they escalate quickly if ignored.
If you notice any of these signs, stop driving immediately. Continuing to drive with a crank hub issue can turn a £3,000 repair into a £12,000 engine replacement. For related timing issues, see our engine knocking noise guide.
The S55 engine uses a two-piece crank hub design. The hub is pressed onto the crankshaft and secured with a single central bolt. Under high torque loads, the hub can slip on the crankshaft, causing the timing chains to jump. The primary reasons are:
The keyless crank hub design is the root cause – it's a well-known weakness that BMW never fully addressed. For a broader view of S55 issues, see our S55 timing chain guide.
| Model | Chassis | Engine | Years | Risk Level |
|---|---|---|---|---|
| M3 (F80) | F80 | S55B30 | 2014–2020 | Very common |
| M4 (F82/F83) | F82 | S55B30 | 2014–2020 | Very common |
| M2 Competition (F87) | F87 | S55B30 | 2018–2021 | Common |
The S55 engine was used in all F80 M3, F82/F83 M4, and F87 M2 Competition models. Early‑production engines (pre‑2016) are particularly susceptible, but all S55 engines can suffer from crank hub failure, especially if tuned. Always verify your specific vehicle's service history and tuning status. For complete chassis‑specific detail, see our fitment matrix.
Frequent hard launches, aggressive downshifts, and sustained high‑RPM use place the most stress on the crank hub. Track use and tuned cars are at significantly higher risk.
Aftermarket engine tuning increases torque output, which directly increases the load on the crank hub. Most catastrophic failures occur on tuned cars, especially those with increased boost.
Failures can occur at any mileage, but most happen between 20,000 and 60,000 miles. Early‑production engines (2014–2016) have a higher incidence of failures.
A BMW‑compatible diagnostic tool will read fault codes from the engine control unit (ECU). Common codes include P0015 (camshaft timing over‑retarded) and P0016 (crankshaft/camshaft correlation).
The specialist will manually verify the timing by checking the position of the camshafts relative to the crankshaft. A deviation of even a few degrees indicates hub slippage.
With the front timing cover removed, the specialist can inspect the crank hub for signs of slipping, such as witness marks or damage to the hub and crankshaft.
If you're experiencing symptoms but aren't sure, our Diagnostic Wizard can help narrow it down.
The cost of addressing S55 crank hub failure depends on the extent of damage. Early intervention can save you thousands, but once the hub slips catastrophically, a rebuild or replacement is unavoidable.
| Component / Repair | Supply & Fit (Indie) | Main Dealer Est. |
|---|---|---|
| Crank Hub Fix (preventative, no damage) | £3,000–£4,500 [EM-QUOTE] | £5,000–£7,000 |
| Hub Fix + Timing Reset (minor slip) | £4,000–£6,000 | £6,000–£9,000 |
| Hub Fix + Valve/Piston Repair (if contact occurred) | £6,000–£9,000 | £9,000–£14,000 |
| Used Engine Replacement | £8,000–£12,000 | £12,000–£18,000 |
| Reconditioned Engine Replacement | £12,000–£16,000 | £16,000–£22,000 |
Labour is a major cost – 14–20 hours at £65–£100/hr. Prices are indicative for 2025; always obtain a written quote for your specific vehicle. For full cost data, see our average replacement cost page.
While the crank hub is a design weakness, there are steps you can take to reduce the risk of failure.
For more detailed economics, see our Repair vs Replace vs Scrap Framework.
⚠️ Caution — depends on the extent of damage.
Our data flags S55 crank hub repairs as Caution against the 70% BMW threshold. A preventative hub upgrade is a small fraction of the car's value and is highly recommended. However, if the hub has already slipped and caused valve damage, the repair cost can approach or exceed 70% of an older M car's value. For most owners, a preventative fix is a wise investment, but a catastrophic failure may push the car into scrap territory. See the full economics framework for a worked example.
If you're still uncertain, compare this failure to the S55 timing chain guide or read real owner decisions in our case studies section.
The first sign is usually an intermittent engine warning light with timing‑related fault codes (P0015, P0016). You may also notice a slight hesitation under acceleration or a lumpy idle.
This is a major job that requires removing the front timing cover, verifying timing, and installing a new hub. It is not a DIY task – specialist tools and experience are essential to avoid catastrophic engine damage.
Preventative hub replacement (with a keyed or upgraded hub) typically costs £3,000–£4,500 at an independent specialist. If the hub has already slipped and caused damage, the cost can rise to £6,000–£9,000 or more.
It depends on the car's overall condition and value. A preventative job is almost always worth it, as it preserves the car's reliability and value. However, if the engine has already failed, the repair may be uneconomical on a low‑value example.
BMW's repair-or-scrap threshold is 70% of the vehicle's market value. If the fitted replacement cost exceeds 70% of what your BMW is worth, it may be financially wiser to scrap or sell the car rather than repair. Use the Repair vs. Replace Calculator to decide.
There is no official recall for the crank hub on the S55, as BMW considers it a design feature rather than a defect. However, many specialists recommend upgrading the hub as a preventative measure. Check with your dealer for any applicable service actions.
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