Mercedes-Benz OM660 Specifications
| Engine Model: Mercedes-Benz OM660 |
| Engine Type: 4-cycle 3-cylinder SOHC 6-valve turbocharged liquid-cooled diesel |
| Total Displacement: 48.8 cu.in (0.79 L) |
| Rated Engine Power: 40-53 Hp (30-40 kW) at 4200 rpm |
| Fuel System Type: Common rail direct injection |
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The Mercedes-Benz OM660 is an ultra-compact,
turbocharged inline-three diesel engine developed specifically for the Smart
Fortwo. Produced between 1999 and 2014, the OM660 held the distinction of being
the smallest common-rail diesel engine in mass production during its
manufacturing run. The engine was engineered for extreme fuel efficiency and low
CO2 emissions, utilizing an all-aluminum construction to minimize mass.
The OM660 is mounted at a steep 45-degree angle within the Smart’s rear-engine,
rear-wheel-drive layout, a configuration that dictated unique lubrication and
cooling system designs. Over its production life, the engine evolved through
multiple power output stages while maintaining its core architecture,
culminating in a Euro 5-compliant variant with a diesel particulate filter.
Engine Type: Inline 3-cylinder, 4-cycle, water-cooled, turbocharged diesel.
Displacement: 799 cc (48.8 cu.in).
Bore: 65.5 mm (2.58 in).
Stroke: 79.0 mm (3.11 in).
Compression Ratio: 18.0:1 for early variants (1999-2006).
Compression Ratio: 18.5:1 for late variants (2007-2014).
Firing Order: 1-2-3.
Maximum Power
First generation (1999-2006): 41 PS (40 hp / 30 kW) @ 4,200 rpm.
Second generation (2007-2009): 45 PS (44 hp / 33 kW) @ 4,200 rpm.
Final revision (2009-2014): 54 PS (53 hp / 40 kW) @ 4,200 rpm.
Maximum Torque
First generation (1999-2006): 100 Nm (74 lb-ft) @ 1,800-2,400 rpm.
Second generation (2007-2009): 110 Nm (81 lb-ft) @ 2,000-2,500 rpm.
Final revision (2009-2014): 130 Nm (96 lb-ft) @ 2,000-2,500 rpm.
Valvetrain Configuration: Single Overhead Camshaft (SOHC), 6 valves (2 valves
per cylinder).
The camshaft is driven by a toothed timing belt.
Valve clearances are maintained by hydraulic lash adjusters, eliminating routine
manual adjustment.
The cylinder block is manufactured from aluminum alloy
with cast-in iron cylinder liners to provide wear-resistant bore surfaces. Bore
diameter measures 65.5 mm (2.58 in). The block features a compact, open-deck
design optimized for the engine’s 45-degree installation angle in the Smart
Fortwo’s rear-engine compartment. The crankshaft is forged steel with four
counterweights, supported by four main bearings.
The block incorporates an integrated oil gallery system feeding the main
bearings, connecting rods, and camshaft bearings. The sump is a shallow aluminum
casting with internal baffling designed to maintain oil pickup under the
inclined mounting orientation. Engine weight is 60 kg (132 lb) dry.
The cylinder head is manufactured from aluminum alloy
with a cross-flow port architecture.
Valves: 6 total; 3 intake, 3 exhaust.
Intake Valve Diameter: 28.0 mm (1.10 in).
Exhaust Valve Diameter: 26.0 mm (1.02 in).
Valve Stem Diameter: 5.0 mm (0.20 in) for both intake and exhaust.
Valve Seat Inserts: Sintered alloy inserts with multi-angle seat geometry.
Valve Guides: Press-fit sintered iron guides.
Hydraulic Lash Adjusters: Direct-acting units mounted in the cylinder head
casting, operating on bucket-type cam followers. These adjusters automatically
maintain zero valve clearance throughout engine life. Camshaft: Hollow cast iron
camshaft with induction-hardened lobes. The camshaft is supported by four
bearings and driven by a toothed timing belt.
Combustion Chamber: Re-entrant bowl design within the piston crown, optimized
for swirl generation with the common rail injection system. Glow Plugs: Ceramic
or steel sheathed glow plugs with rapid heating capability. Post-heating
continues after start to reduce cold start emissions and improve combustion
stability.
The fuel system employs a common rail direct injection
system with solenoid or piezoelectric injectors depending on production year.
Injection Type: Direct injection into the combustion chamber with centrally
mounted injectors. Injection Pump: Bosch CP1 or CP3 high-pressure pump driven by
the timing belt. The pump incorporates a fuel metering valve to regulate rail
pressure.
Injector Configuration
Early variants (1999-2006): Solenoid-actuated injectors with five-hole nozzles.
Rail pressure up to 1,350 bar (19,580 psi).
Late variants (2007-2014): Solenoid or piezoelectric injectors with seven-hole
nozzles for improved atomization. Rail pressure up to 1,600 bar (23,206 psi).
Fuel Filtration: Spin-on cartridge fuel filter with an integrated water
separator. The filter incorporates a thermostatic bypass for cold-start fuel
flow. Fuel Pressure: Rail pressure varies from 250-300 bar (3,625-4,350 psi) at
idle to a maximum of 1,350-1,600 bar (19,580-23,206 psi) under full load,
depending on variant. Engine Management System: Bosch EDC15 or EDC16 electronic
control unit managing injection timing, rail pressure, boost control, and glow
plug operation.
The lubrication system is a full-flow, pressurized
design utilizing a rotor-type oil pump driven by the crankshaft, with specific
adaptations for the engine’s 45-degree installation angle. Oil Pump Type:
Internal gear (gerotor) pump mounted to the front of the crankshaft. The oil
pickup is positioned within a baffled sump to maintain oil supply under all
vehicle attitudes and the inclined engine orientation.
Oil Capacity: 3.2-3.5 liters (3.4-3.7 qt) including oil filter replacement.
Recommended Oil Viscosity: 0W-30 or 5W-30. Oil Quality Requirement: ACEA C2 or
C3 (low-ash formulation) for models equipped with a Diesel Particulate Filter
(DPF). ACEA B4 for early non-DPF variants.
Oil Pressure: At warm idle, pressure ranges from 1.0-1.5 bar (14-22 psi). At
3,000 rpm, pressure reaches 3.0-4.0 bar (44-58 psi). Oil Cooler: Liquid-to-oil
plate-type heat exchanger integrated into the oil filter housing, utilizing
engine coolant for thermal stabilization. Oil Filter: Cartridge-type filter
housed within a modular housing accessible from the engine top or under-vehicle
location depending on Smart chassis configuration.
The cooling system is pressurized and utilizes a
centrifugal water pump driven by the timing belt. Water Pump Type: Centrifugal
pump with an aluminum housing and stamped steel impeller. Thermostat: Wax-pellet
type located in the coolant outlet housing. Opening temperature is 82-88 °C
(180-190 °F).
Coolant Capacity: 4.5-5.0 liters (4.8-5.3 qt) inclusive of engine block, heater
core, and radiator. System Pressure: Radiator cap rated at 1.1 bar (16 psi).
Coolant Specification: Phosphate and silicate-free ethylene glycol-based coolant
meeting Mercedes-Benz specifications for aluminum engine construction.
Radiator: Front-mounted cross-flow aluminum core with plastic end tanks. Coolant
is routed from the rear-mounted engine to the front radiator through underfloor
pipes. Cooling fan configuration consists of a single electric fan with variable
speed control.
Timing System: Toothed timing belt constructed from
high-tensile rubber with fiber reinforcement. The belt drives the camshaft,
high-pressure fuel pump, and water pump. An automatic spring-loaded tensioner
maintains belt tension. Replacement interval is 90,000 km (56,000 miles) or 5
years.
Turbocharger System: Single turbocharger with fixed geometry or variable nozzle
turbine (VNT) depending on production year. Maximum boost pressure ranges from
1.0-1.2 bar (14.5-17.4 psi) absolute. The turbocharger is water-cooled for
thermal management after engine shutdown.
Intercooler: Air-to-air intercooler mounted in the front bumper area, connected
to the engine by charge air pipes routed under the vehicle floor.
Exhaust System: Cast iron exhaust manifold with integrated turbocharger mounting
flange. A Diesel Oxidation Catalyst (DOC) is standard on all variants. Later
models (2009-2014) incorporate a Diesel Particulate Filter (DPF) with
closed-loop regeneration management.
Intake Manifold: Composite plastic manifold with integrated intake air
temperature sensor and throttle flap for engine shutdown control.
Crankcase Ventilation: Closed-loop system with an integrated oil separator
incorporated into the valve cover. Blow-by gases are routed to the turbocharger
compressor inlet.
Engine Mounting: The engine is mounted at a 45-degree angle to the vehicle
centerline using three elastomeric mounts, allowing compact packaging within the
Smart’s rear-engine compartment.
Overall Length: 480 mm (18.9 in) measured from
accessory drive pulley face to transmission mounting flange.
Overall Width: 580 mm (22.8 in) inclusive of intake manifold, turbocharger, and
injection system components.
Overall Height: 620 mm (24.4 in) from oil pan bottom surface to valve cover top
surface measured in the installed 45-degree orientation.
Dry Weight: 58-62 kg (128-137 lb) depending on turbocharger configuration and
emissions equipment.
Timing Belt Replacement Interval: 90,000 km (56,000
miles) or 5 years, whichever occurs first. Replacement includes the belt,
tensioner, and idler pulley. Fuel Filter Replacement Interval: 30,000 km (18,600
miles) or as indicated by water-in-fuel sensor.
Engine Oil Change Interval: 10,000 km (6,200 miles) or 12 months for standard
driving conditions; 7,500 km (4,700 miles) for severe service. Coolant Change
Interval: 60,000 km (37,000 miles) or 3 years. Glow Plug Replacement Interval:
Replace as required; functional inspection recommended at 80,000 km (50,000
miles). Idle Speed (warm, neutral): 850-900 rpm.
Injection Timing: Electronically controlled with closed-loop feedback from
oxygen sensors and crankshaft position; no manual adjustment possible. Valve
Timing (synchronization): Crankshaft positioned at top dead center (TDC) No. 1
cylinder. Camshaft sprocket alignment mark aligned with cylinder head pointer.
Crankshaft sprocket alignment mark aligned with timing case mark.
Cylinder Head Bolts (cold), Step 1: 20 Nm (15 lb-ft).
Cylinder Head Bolts (cold), Step 2: 40 Nm (30 lb-ft) plus 90° rotation.
Crankshaft Damper Pulley Bolt: 150-160 Nm (111-118 lb-ft).
Connecting Rod Cap Bolts: 20 Nm (15 lb-ft) plus 90° rotation.
Main Bearing Cap Bolts: 30 Nm (22 lb-ft) plus 90° rotation.
Camshaft Bearing Cap Bolts: 10-12 Nm (7-9 lb-ft).
Camshaft Sprocket Bolt: 60-70 Nm (44-52 lb-ft).
Valve Cover Bolts: 8-10 Nm (6-7 lb-ft).
Intake Manifold Bolts: 18-22 Nm (13-16 lb-ft).
Exhaust Manifold Nuts: 25-30 Nm (18-22 lb-ft).
Turbocharger Mounting Nuts: 30-35 Nm (22-26 lb-ft).
Oil Pan Bolts: 8-10 Nm (6-7 lb-ft).
Timing Belt Tensioner Bolt: 20-25 Nm (15-18 lb-ft).
Water Pump Bolts: 18-22 Nm (13-16 lb-ft).
High-Pressure Fuel Pump Mounting Bolts: 20-25 Nm (15-18 lb-ft).
Fuel Injector Clamp Bolts: 25-30 Nm (18-22 lb-ft).
Glow Plugs: 20-25 Nm (15-18 lb-ft).
Flywheel / Drive Plate Bolts: 70-80 Nm (52-59 lb-ft).
Engine Mount Bracket Bolts: 40-45 Nm (30-33 lb-ft).
Smart Fortwo (450 series, City-Coupe / Cabrio):
1999-2006 model years. The OM660 was introduced as the 0.8 cdi (common rail
diesel) variant, producing 41 PS (30 kW) and 100 Nm (74 lb-ft). This generation
utilized the Euro 3 emissions standard and did not incorporate a Diesel
Particulate Filter.
Smart Fortwo (451 series): 2007-2014 model years. The OM660 received progressive
power upgrades throughout the 451 production cycle. Initial 2007-2009 variants
produced 45 PS (33 kW) and 110 Nm (81 lb-ft). Final revisions from 2009-2014
produced 54 PS (40 kW) and 130 Nm (96 lb-ft), incorporating a Diesel Particulate
Filter and achieving Euro 5 emissions compliance. The engine remained in
production until the discontinuation of the diesel Fortwo in 2014.
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