BMW M4 S55
"Did the crank hub the day I picked mine up, no way I'm trusting the stock friction-fit part past 20k miles on a car that gets tracked. Outside of that it's just HPFP and carbon build-up like every other BMW direct injection engine, mine's on 90k km and still pulls hard to 7500."
Power Variants
Recommendation
The core hardware is identical across the base and Competition tunes, the extra power comes from ECU mapping so reliability is essentially the same, buy on condition and documented maintenance rather than the hp figure. The GTS is the outlier: its water injection system is an added maintenance and failure point, check the reservoir, pump, and nozzles specifically on a GTS since a failed system reverts the car to a safer but weaker map. CS models share more hardware with the GTS but skip water injection, so their risk profile is closer to the standard Competition engine. On any variant, crank hub status matters more than power output.
Known Issues
Crank Hub Slipping (Friction-Fit Design Weakness)CRITICAL
The S55 uses a friction-fit crank hub rather than a keyed design. Under high load, hard track use, or with tuned cars pushing more torque, the hub can slip on the crankshaft, causing catastrophic timing loss and potential engine destruction. BMW never redesigned the part and handled failures under warranty instead. Aftermarket keyed crank hub kits are considered a mandatory upgrade by the tuning community, especially on any car that sees track time or has been tuned.
High-Pressure Fuel Pump (HPFP) FailureHIGH
HPFP failure is a known issue across BMW's direct-injection lineup including the S55. Failure can be sudden and can leave the car undriveable. This is one of the most frequently cited reliability complaints on S55 forums.
Carbon Build-Up on Intake ValvesHIGH
As a direct-injection engine, the S55 does not wash intake valves with fuel, so carbon deposits build up on the back of the intake valves over time. This reduces airflow and causes rough running. This is a well documented recurring issue on the S55 and its BMW direct-injection relatives.
Intercooler Leaks (OEM and Aftermarket Units)MODERATE
OEM intercoolers on the S55 have been reported to develop leaks over time, reducing charge-air cooling efficiency and boost pressure. Poorly fitted aftermarket intercoolers can introduce the same fault sooner.
Oil Consumption and Cooling System Stress Under Track UseMODERATE
The S55 has additional oil cooling built in for track use, but cars driven hard on track need close oil level monitoring. Elevated oil consumption and cooling system wear show up more often on cars with a track history.
Official Recalls
Inflator may deploy with excessive force, posing injury risk to occupants.
Inflator may rupture upon deployment, sending metal fragments toward occupants.
Buying Checklist
Service Reality
Strong Points
Also Found In
Time Bomb Parts Inspect Proactively
Tuning Risk If This Example Has Been Modified
HIGHBootmod3 and MHD, the two dominant flashing platforms for this engine, can return the DME to a genuine factory-equivalent state without needing a prior stock backup, so a stock-reading OBD scan after a reflash is not proof the car was never tuned. JB4 can simply be unplugged and removed, leaving no ECU-side trace. This engine's most serious tuning risk, a spun crank hub, does not reliably announce itself in advance: the OEM hub is intentionally a sacrificial 'fuse' that can throw a fault code on mild slippage, but a car can also have been run hard on an aggressive tune for a long period with no code at all until it finally lets go. Buyer guides specific to this model add a further wrinkle: cars with the dual-clutch (DCT) transmission are described as noticeably more prone to crank hub issues than manual cars, due to the shock loading from the DCT's kick-down behavior, so a DCT car's transmission type itself is a relevant risk factor independent of anything visible in an OBD scan.
Specialist consensus treats a pinned or one-piece crank hub, sound oiling (baffled pan, and for track cars sometimes a secondary oil pump), and an upgraded charge pipe as prerequisites before serious tuning on this engine, not optional add-ons. A car showing Stage 2 or Stage 3 power claims without any mention of a crank hub upgrade is regarded within the community as a meaningfully riskier buy than an otherwise identical car with documented preventative work, particularly if it is a DCT car, given both the catastrophic nature of a crank hub failure and this platform's documented driveline stress points.
This profile reflects consensus from Bimmerfest, F80/M3cutters and Bimmerpost forums, SpoolStreet's technical discussion threads, and multiple S55-specialist and buyer's-guide write-ups (MMX, ARM Motorsports, Esse Werks, Machines with Souls, JXL Performance), not manufacturer-confirmed limits or a BMW-acknowledged tuning-related defect rate. Crank hub failure rates and the DCT-vs-manual risk difference cited by these sources are specialist and owner estimates, not warranty or recall data (the driveshaft/differential recalls referenced are genuine NHTSA recalls but are separate from tuning-specific risk). Treat any suspected tuned or previously tuned S55, especially a DCT car, as needing a full pre-purchase inspection, ideally including a compression/leak-down check, a careful listen for rod knock on a cold start, a check for rear-end clunking, and a direct question to the seller about crank hub and oil pan preventative work, rather than relying on an OBD scan alone.
Buying Advice
The S55 is a genuinely capable engine that holds up well when properly maintained, but it rewards diligent owners and punishes neglect. The single most important pre-purchase item is confirming the crank hub has been upgraded to a keyed aftermarket unit, buying a used car with the stock friction-fit hub still fitted is a real risk, especially if the car has ever been tracked or tuned. Budget for walnut blasting and a fresh HPFP check early in ownership since these are the two most common costly failures after the crank hub. Power output differences between the base, Competition, CS, and GTS variants come mostly from ECU tuning and shared hardware, so buy on documented maintenance and crank hub status rather than the hp figure on the spec sheet. A well-serviced, high-mileage example with the crank hub already done can be a genuinely reliable performance engine.
Community Sentiment
Generally positive among experienced BMW M owners who maintain the car properly. The consensus is that the S55 is meaningfully more robust than the preceding N54/N55 turbo four and six cylinder engines when serviced correctly. The crank hub issue is the single most discussed concern and dominates pre-purchase conversations, followed by HPFP and carbon build-up questions common to all BMW direct-injection engines.
Frequently Asked Questions
❯How reliable is the BMW M4 S55?
The BMW M4 S55 has a reliability score of 60/100, rated "SOLID". Strong M engine, but the crank hub upgrade is non-negotiable
❯What are the common problems with the S55?
The most frequently reported issues are Crank Hub Slipping (Friction-Fit Design Weakness), High-Pressure Fuel Pump (HPFP) Failure, Carbon Build-Up on Intake Valves, Intercooler Leaks (OEM and Aftermarket Units), among others. See the Known Issues section above for symptoms, affected mileage, and repair costs.
❯Does the S55 have crank hub slipping (friction-fit design weakness) problems?
Yes, this is a documented issue on the S55, typically appearing around 30,000–120,000 km. The S55 uses a friction-fit crank hub rather than a keyed design. Under high load, hard track use, or with tuned cars pushing more torque, the hub can slip on the crankshaft, causing catastrophic timing loss and potential engine destruction. BMW never redesigned the part and handled failures under warranty instead. Aftermarket keyed crank hub kits are considered a mandatory upgrade by the tuning community, especially on any car that sees track time or has been tuned. Typical repair cost: €600–1,500. DIY difficulty: Hard, requires special tooling and engine bay access.
❯Does the S55 have high-pressure fuel pump (hpfp) failure problems?
Yes, this is a documented issue on the S55, typically appearing around 60,000–150,000 km. HPFP failure is a known issue across BMW's direct-injection lineup including the S55. Failure can be sudden and can leave the car undriveable. This is one of the most frequently cited reliability complaints on S55 forums. Typical repair cost: €600–1,500. DIY difficulty: Moderate, accessible but requires fuel system knowledge.
❯Does the S55 have carbon build-up on intake valves problems?
Yes, this is a documented issue on the S55, typically appearing around 60,000–120,000 km. As a direct-injection engine, the S55 does not wash intake valves with fuel, so carbon deposits build up on the back of the intake valves over time. This reduces airflow and causes rough running. This is a well documented recurring issue on the S55 and its BMW direct-injection relatives. Typical repair cost: €400–900. DIY difficulty: Hard, requires intake manifold removal and specialist equipment.
❯Does the S55 have intercooler leaks (oem and aftermarket units) problems?
Yes, this is a documented issue on the S55, typically appearing around 50,000–130,000 km. OEM intercoolers on the S55 have been reported to develop leaks over time, reducing charge-air cooling efficiency and boost pressure. Poorly fitted aftermarket intercoolers can introduce the same fault sooner. Typical repair cost: €300–900. DIY difficulty: Moderate, accessible with basic tools.
❯Does the S55 have oil consumption and cooling system stress under track use problems?
Yes, this is a documented issue on the S55, typically appearing around 40,000–100,000 km. The S55 has additional oil cooling built in for track use, but cars driven hard on track need close oil level monitoring. Elevated oil consumption and cooling system wear show up more often on cars with a track history. Typical repair cost: €200–600. DIY difficulty: Easy for monitoring, repairs vary by root cause.
❯Is the S55 worth buying used?
The S55 is a genuinely capable engine that holds up well when properly maintained, but it rewards diligent owners and punishes neglect. The single most important pre-purchase item is confirming the crank hub has been upgraded to a keyed aftermarket unit, buying a used car with the stock friction-fit hub still fitted is a real risk, especially if the car has ever been tracked or tuned. Budget for walnut blasting and a fresh HPFP check early in ownership since these are the two most common costly failures after the crank hub. Power output differences between the base, Competition, CS, and GTS variants come mostly from ECU tuning and shared hardware, so buy on documented maintenance and crank hub status rather than the hp figure on the spec sheet. A well-serviced, high-mileage example with the crank hub already done can be a genuinely reliable performance engine.
❯Should I buy a BMW M4 with the S55 engine?
The core hardware is identical across the base and Competition tunes, the extra power comes from ECU mapping so reliability is essentially the same, buy on condition and documented maintenance rather than the hp figure. The GTS is the outlier: its water injection system is an added maintenance and failure point, check the reservoir, pump, and nozzles specifically on a GTS since a failed system reverts the car to a safer but weaker map. CS models share more hardware with the GTS but skip water injection, so their risk profile is closer to the standard Competition engine. On any variant, crank hub status matters more than power output.
❯What should I check before buying a used S55?
Before buying, check: Confirm an aftermarket keyed crank hub has been installed, this is close to a non-negotiable upgrade on any S55, especially a tracked or tuned car; Request evidence of walnut blasting or a borescope inspection of the intake valves within the last 60,000 km; Pressure test the intercooler system and inspect all hoses and end tanks for leaks or coolant staining; Read fault codes with a BMW-compatible OBD tool, specifically check for HPFP and timing-related codes; Check oil level and condition, ask for service records showing oil changes no longer than every 8,000 km.
❯How many km will a S55 last?
There's no fixed mileage limit, it depends on maintenance. The parts worth budgeting for proactively are: Crank Hub (Before 30,000 km or at purchase), Intake Valves (Carbon Build-Up) (Every 60,000–80,000 km), High-Pressure Fuel Pump (80,000–120,000 km), Intercooler Assembly (60,000–100,000 km). Engines that clear these checkpoints with documented maintenance commonly continue well beyond typical ownership periods.
❯Is there a recall for the side/window airbags on the S55?
Inflator may deploy with excessive force, posing injury risk to occupants. Remedy: Inspect and replace affected airbag inflator modules as directed by BMW.
❯Is there a recall for the frontal driver side airbag inflator module on the S55?
Inflator may rupture upon deployment, sending metal fragments toward occupants. Remedy: Replace airbag inflator module under recall program.
❯How much does it cost to maintain a S55?
Estimated ownership cost is €4,500–9,000 over 3 years depending on track use, crank hub status at purchase, and whether HPFP or intercooler work is needed, based on known issues and typical service needs.
❯What is the real-world fuel consumption of the S55?
Owners report real-world fuel consumption of around 10 L/100km, compared to the official figure of 10.2 L/100km.
❯What oil should I use in a S55, and how often?
Community-reported real-world usage suggests changing oil every 8,000 km using BMW LL-04 compliant 0W-40 or 10W-60 for track use (e.g. Castrol TWS 10W-60), often more conservative than the official service schedule.
❯Is it safe to tune or remap the S55?
The S55 is commonly modified, with a high risk level when pushed beyond stock. Typical weak points under tuning: Crank hub (front crank timing drive), Rod bearings / oil supply, Rear differential / driveshaft, Factory charge pipe.
❯What other cars use the S55 engine?
The S55 is also found in: BMW M3 F80 (2014–2018), BMW M4 F82/F83 (2014–2020), BMW M3 CS / M4 CS (2017–2019), BMW M4 GTS F82 (2016, limited production), BMW M2 Competition F87 (2018–2021).
❯What do owners say about the S55?
Generally positive among experienced BMW M owners who maintain the car properly. The consensus is that the S55 is meaningfully more robust than the preceding N54/N55 turbo four and six cylinder engines when serviced correctly. The crank hub issue is the single most discussed concern and dominates pre-purchase conversations, followed by HPFP and carbon build-up questions common to all BMW direct-injection engines.