BMW S55 Common Problems & Reliability
The twin-turbo S55 in the F80 M3 is a brilliant, hugely tunable engine — but it's an M motor, and two issues define ownership: the crank hub and the rod bearings. Understand those, keep on top of the turbo wear items, and it's a deeply rewarding car. Here's the honest breakdown.
The S55 marked the M3's switch to forced induction — a closed-deck, twin-turbocharged straight-six making around 425 hp (444 in Competition trim) and a colossal amount more once tuned. It's strong and responsive, and the aftermarket is huge. But like any M engine it rewards diligent ownership, and there are two items every buyer must price into the decision before anything else.
The crank hub is the defining S55 concern
The S55's crankshaft hub is a friction (press) fit that drives the timing system — and under the extra torque of a tune, it can slip, throwing off timing and risking serious engine damage. Many owners "pin" the crank hub (mechanically locking it) as preventive insurance, especially before or soon after tuning. On a tuned F80, addressed crank hub history is close to essential — see our crank hub guide.
The short version
The S55 is robust and tunable, but buy with the crank hub addressed (or budget the pinning), check the rod-bearing history and oil condition, and confirm the smaller turbo items — charge pipes, cooling and a wastegate rattle — have been sorted. A well-kept, sensibly tuned F80 is a superb car; a hammered, undocumented one can be a money pit.
The Two That Matter Most
Price these into any F80 purchase.
- Friction-fit design — the press-fit crank hub can slip, especially with the added torque of a tune, upsetting timing.
- Worst case is serious — slipped timing on a running engine risks major damage, so it's not to be ignored.
- The fix is pinning — mechanically locking the hub (or an upgraded hub) is the accepted preventive cure, popular before or with a tune.
- Buy one that's done — on a tuned F80, documented crank-hub work is close to essential; on a stock car, factor it in.
- A known M consideration — like other M engines, the S55's rod bearings are a wear item owners watch.
- Preventive replacement — many owners replace the bearings at intervals (sooner on tracked or hard-driven cars) as insurance.
- It's debated — how necessary and how often is argued, but oil analysis and history help you judge a given car.
- Ask & check — find out whether (and when) they've been done, and review oil condition or any oil analysis. See our rod bearings guide.
The Smaller Stuff
Turbo wear items — mostly cheap, but check them.
- Charge pipes — the plastic OEM charge pipes crack under boost (especially when tuned); aluminum replacements are a cheap, common fix.
- Cooling system — a twin-turbo M engine makes heat; the electric water pump, expansion tank and coolant are wear items, and track use stresses cooling.
- Wastegate rattle — the turbos can develop a rattle from the wastegate arms; common and more annoyance than failure, but note it.
- Carbon buildup — direct injection collects intake-valve carbon over time; periodic walnut blasting keeps it breathing.
- Oil consumption — M engines can use some oil; check the level (electronic) and keep it topped to spec.
- DCT service — where fitted, the 7-speed DCT is robust but wants its fluid and filter serviced on schedule.
What to Check Before Buying
An M car lives hard — history is everything.
- Crank hub: on a tuned car especially, confirm it's been pinned or addressed, with documentation.
- Rod bearings: ask whether they've been replaced and when; review oil condition or analysis.
- Tune & track history: how it's been driven, by whom, with what supporting mods — and whether it's seen heavy track use.
- Charge pipes & cooling: check for cracked pipes, a healthy cooling system and any overheating signs.
- Service records: regular M-spec oil changes, fluids and DCT service (if fitted).
- Codes & basics: scan for faults, and run the standard checks — brakes, tyres, body and electronics.
Owning One
An F80 is a usable supercar-killer, but it has M-car running costs: it goes through brakes and tyres faster than a regular 3 Series, wants diligent fluid and cooling care, and — if tuned — the crank hub and rod bearings are real budget lines. Buy a documented, sensibly modified car and it's hugely rewarding. Detailed guides live on the F80 hub; keep a scan tool handy for codes and battery registration.
FAQ
Is the S55 reliable?
Fundamentally it's a strong, capable engine — but it's an M motor with two items that define ownership: the crank hub and the rod bearings. Address those and stay on top of the turbo wear items (charge pipes, cooling), and a well-kept S55 is dependable. A neglected or hard-tuned, undocumented one is the risk.
What is the crank hub problem?
The S55's crankshaft hub is a friction (press) fit that drives the timing system, and it can slip — especially under the added torque of a tune — upsetting timing and risking engine damage. The accepted fix is "pinning" the hub to lock it mechanically. A dedicated guide is on the F80 hub.
Do I need to replace the rod bearings?
It's debated. Like other M engines, the S55's rod bearings are a wear item, and many owners replace them preventively at intervals — sooner on tracked or hard-driven cars. Whether and when is a judgment call; ask about history and review oil condition to decide on a given car.
Is a tuned S55 safe to buy?
It can be, if it's done right — a sensible tune with supporting mods, a pinned crank hub and good records is fine. Be wary of a heavily tuned, hard-tracked car with no documentation, where the crank hub and bearings may be at risk.
What about charge pipes and wastegate rattle?
The plastic OEM charge pipes crack under boost and are commonly swapped for aluminum — cheap and easy. A wastegate rattle from the turbos is also common and usually more annoyance than failure, but note it and factor it in.
Is the DCT reliable?
The 7-speed DCT is robust and a joy to use, but it needs its fluid and filter serviced on schedule. Confirm that service history on a DCT car; a neglected gearbox is best avoided.
The Bottom Line
The S55 is a thrilling, tunable M engine that's dependable when bought and kept right. The two non-negotiables are the crank hub (have it pinned, especially if tuned) and the rod bearings (know the history); the rest — charge pipes, cooling, the odd wastegate rattle — is routine turbo upkeep. Find a documented, sensibly modified F80 and it's one of the great modern M cars. Read the dedicated guides on the F80 hub.