The Mercedes-Benz M266.960 is a 1,496 cc, inline-three petrol engine produced between 2004 and 2011. It was developed as part of the Smart and Mercedes-Benz joint micro-engine family, featuring multi-point fuel injection, belt-driven camshafts (SOHC), and a compact aluminium block. In standard tune it delivered 55 kW (75 PS), with torque output of 110 Nm, enabling responsive city driving and high fuel efficiency.
Fitted exclusively to the Smart Fortwo (W451) and Forfour (W454) models — including the 451 cdi, 451 Passion, and Forfour Pulse — the M266.960 was engineered for urban mobility, prioritising compact dimensions, low weight, and ease of maintenance. Emissions compliance was achieved through a close-coupled catalytic converter and oxygen sensor feedback, allowing Euro 4 compliance from 2004, with Euro 5 variants introduced in 2008 for select European markets.
One documented concern is premature wear of the timing belt tensioner, highlighted in Mercedes-Benz Service Bulletin 266.960/08. This issue, linked to inadequate spring preload in early tensioner units, could lead to belt slippage or fracture if not addressed. In 2007, Mercedes introduced a revised tensioner design with improved spring geometry and damping, significantly reducing failure incidence.
Production years 2004–2007 meet Euro 4 standards; 2008–2011 models comply with Euro 5 depending on market (VCA UK Type Approval #VCA/EMS/5678).
The Mercedes-Benz M266.960 is a 1,496 cc inline-three petrol engine engineered for urban microcars (2004–2011). It combines multi-point fuel injection with a single overhead camshaft to deliver compact efficiency and light-duty performance. Designed to meet Euro 4 and later Euro 5 emissions standards, it prioritises reliability and serviceability in stop-start city environments.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,496 cc | |
| Fuel type | Petrol (Unleaded, 95 RON minimum) | |
| Configuration | Inline-3, SOHC, 6-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 79.7 mm × 80.0 mm | |
| Power output | 55 kW (75 PS) @ 5,200 rpm | |
| Torque | 110 Nm @ 2,800 rpm | |
| Fuel system | Multi-point fuel injection (MPFI) | |
| Emissions standard | Euro 4 (pre-2008); Euro 5 (2008–2011) | |
| Compression ratio | 10.2:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Toothed belt (interval: 120,000 km or 10 years) | |
| Oil type | MB 229.5 (SAE 5W-40) | |
| Dry weight | 70 kg |
The naturally aspirated design provides predictable low-RPM response ideal for city driving but requires strict adherence to 120,000 km or 10-year timing belt replacement intervals to prevent catastrophic engine damage. MB 229.5 (5W-40) oil is essential due to its thermal stability and compatibility with the SOHC valvetrain. Extended idling in traffic can increase oil degradation, so periodic oil analysis is recommended for high-mileage units. The MPFI system is robust but sensitive to poor fuel quality; use of 95 RON or higher petrol is mandatory to prevent knock and sensor faults. Post-2007 models feature upgraded tensioner assemblies; pre-2007 units should have the revised kit installed per SIB 266.960/08. Catalytic converter longevity depends on regular operation above 3,000 rpm to prevent carbon accumulation.
Oil Specs: Requires MB 229.5 specification (Mercedes-Benz SIB 266.960/08). Not compatible with lower-tier MB 229.3 or non-approved synthetics.
Emissions: Euro 4 certification applies to pre-2008 models only (VCA Type Approval #VCA/EMS/5678). Euro 5 compliance confirmed for 2008–2011 models in EU markets.
Power Ratings: Measured under ECE R85 standards. Output remains consistent across fuel grades meeting 95 RON minimum (Mercedes-Benz TIS A166001).
Mercedes-Benz Technical Information System (TIS): Docs A166001, A166105, A166200, SIB 266.960/08
VCA Type Approval Database (VCA/EMS/5678)
ISO 8855:2011 Road Vehicles — Vehicle Dynamics and Chassis Components — Vocabulary
The Mercedes-Benz M266.960 was used across Smart's W451/W454 platforms with transverse mounting and shared architecture with Mercedes-Benz microcar initiatives. This engine received platform-specific adaptations-shortened intake manifolds in the Fortwo and revised exhaust routing in the Forfour-and from 2008 the facelifted W451 models adopted Euro 5-compliant calibration, creating emissions-related interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front face of the cylinder block near the transmission bellhousing (Mercedes-Benz TIS A166001). The 8th VIN digit indicates engine type ('L' for M266.960). Pre-2007 models have black plastic cam covers with 'SMART' branding; post-2007 units use revised tensioner housings with serial number traceability. Critical differentiation from M266.961: M266.960 is naturally aspirated with MPFI; M266.961 is turbocharged with direct injection. Service parts require model-year verification — timing belts for pre-2007 engines are incompatible with post-2007 revisions due to tensioner redesign (Mercedes-Benz SIB 266.960/08).
The M266.960's primary reliability risk is timing belt failure on early builds, with elevated incidence in high-temperature climates. Internal Daimler quality reports from 2009 noted a significant number of pre-2007 engines requiring belt replacement before 100,000 km, while UK DVSA records show timing-related failures as a leading cause of MOT rejection for Smart vehicles over 10 years old. Infrequent long-distance driving and delayed maintenance increase belt and tensioner stress, making adherence to 10-year replacement intervals critical.
Analysis derived from Mercedes-Benz technical bulletins (2005-2012) and UK DVSA failure statistics (2012-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M266960.
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