Mercedes-Benz M133 engine (2013-on)

Introduction

The Mercedes-Benz M133 was a turbocharged, four-cylinder inline petrol engine that was first introduced in the W176 A 45 AMG in 2013. The M133 engine was hand-produced by MDC Power GmbH in Kölleda, Germany, and key features included its:

• Forged steel crankshaft and forged pistons;
• Twin-scroll turbocharger which provided maximum boost pressure of 1.8 bar (26.1 psi);
• Cross-flow cooling;
• Direct injection;
• Compression ratio of 8.6:1;
• Maximum engine speed of 6700 rpm; and,
• ECO start/stop function with starter-assisted direct starting.

Cylinder block

The crankcase for M133 engine had 83.0 mm bores – spaced at 90 mm intervals – and a 92.0 mm stroke for a capacity of 1991 cc. The crankcase consisted of an aluminium chill casting (with sand grains) and had a closed-deck design (i.e. the engine block cover plate was closed in the area around the cylinders). Furthermore, ventilation bores between the cylinders were embedded in the casting, while several transverse and longitudinal struts were used to increase rigidity.

Within the cylinder bores, twin-wire arc spraying (TWAS) was used to apply a low-friction coating (‘Nanoslide’) that was based on an iron-carbon alloy. Since the Nanoslide coating produced a microporous surface for the cylinder walls, effective lubrication was achieved without the need for cast-iron cylinder liners. According to Mercedes-Benz, the Nanoslide coating reduced friction between the piston, piston rings and cylinder wall by up to 50 per cent and achieved a mass reduction of several kilograms.

The M133 block underwent ‘spectacle honing’, a process in which a jig that resembled spectacles was bolted to the engine block in place of the cylinder head (which was mounted later) and the cylinder liners were subjected to mechanical surface treatment. The honing of the engine block produced the same state of stress as when the cylinder heads were mounted. The tension of the piston rings could therefore be reduced, in turn reducing frictional losses and oil consumption.

The ventilation system of the M133 operated via an oil separator and had ventilation functions for –

• Partial load: the crankcase would be ventilated via a branch fitted with a check valve through the wide open throttle vent line in the opposite direction. Blow-by gases would then be vented from the oil separator to the charge air distribution line; and,
• Wide open throttle (WOT): venting would occur from the oil separator to the clean air line. Blow-by gases would then be removed via the oil separator vent line from the oil filler neck to the oil separator.

Crankshaft, connecting rods and pistons

The M133 engine had a forged steel crankshaft with eight counterweights and the crankshaft bearings caps were made of cast iron with nodular graphite (GGG 60). To reduce vibrations, a viscous damper was mounted on the end of the crankshaft.

The connecting rods for the M133 engine were 138.7 mm long and forged pistons had friction-optimised piston rings. The forged pistons were designed to withstand ignition pressures of up to 140 bar.

Cylinder head

The cylinder head of the M133 engine was made of high-strength aluminium alloy. Within the cylinder head, the intake and exhaust camshafts were driven by the crankshaft via a chain. To minimise noise, the bearings of the guide rail and tensioning rail on the timing case cover were entirely contactless.

The intake camshaft could be ‘advanced’ by up to 40 degrees (relative to the crankshaft) and the exhaust camshaft could be ‘retarded’ by up to 40 degrees so that valve overlap could be varied. The intake and exhaust camshaft solenoids were actuated in response to pulse width modulated (PWM) signals from the ME-SFI control unit. The positions of the intake and exhaust camshaft were measured by Hall sensors.

The M133 engine had two intake and two exhaust valves per cylinder.

Twin-scroll turbocharger

The M133 engine had a twin-scroll turbocharger that was bolted to a fan-type exhaust manifold. As a twin-scroll turbocharger, the spiral housing of the turbine was divided by a flow separator into two parallel flow channels (combining cylinders 1 and 4, and cylinders 2 and 3). In combination with a two-pipe exhaust manifold, this design enabled the exhaust gases to be separately supplied to the turbine wheel to prevent interference between the individual cylinders during the charge cycle. According to Mercedes-Benz, the turbocharger could withstand temperatures of up to 980 degrees Celsius.

The turbocharger drew fresh air through the air filter at the compressor unit and routed it via the compressor outlet into the inlet housing of the charge air cooler. The high speed of the compressor impeller and the resulting high volumetric flow rate compressed the air to a boost pressure of up to 1.8 bar (relative). The compressed, heated charge air then flowed to the charge air cooler, from where it flowed via a charge air hose to the charge air manifold.

The exhaust volume flow rate across the turbine wheel was regulated by the boost pressure control flap. Specifically, the boost pressure control flap could open in order to direct exhaust gases via the wastegate duct (bypass) past the turbine wheel and into the exhaust tract. The boost pressure control transducer was actuated by the ME-SFI control unit according to a characteristics map and according to load.

Charge air cooler

The charge air for the M133 engine was cooled indirectly via a water-cooled charge air cooler that had coolant pumped through it by the low-temperature coolant pump. The absorbed heat was initially dissipated at the wheel arch cooler and then at the low-temperature cooler in the front module.

Injection and ignition

The M133 engine had a single piston high-pressure pump that was positioned at the top of the cylinder head and driven mechanically via the drive plate of the intake camshaft. As such, the delivery rate of the high-pressure pump was rpm-dependent. While the maximum delivery pressure of the pump to the high-pressure rail was 200 bar, pressure was regulated between 100 and 200 bar according to the operating state of the engine. When system pressure was reached, an outlet valve on the pump would open and fuel would be pumped through the high-pressure line to the rail. Furthermore, a pressure limiting valve protected the high-pressure pump from the accumulation of excessive pressure.

For the M133 engine, the soldered fuel rail was made of stainless steel and acted as a high-pressure reservoir for the fuel; the reservoir function damped the oscillations that occurred during the injection process. From the rail, fuel would flow to the centrally-arranged fuel injectors which had piezo actuators. The fuel injectors would spray a calculated quantity of atomised fuel into the combustion chamber; a coupler module in the injection nozzle ensured that the nozzle module and the piezo actuator module did not have longitudinal play. The injectors were capable of providing up to five injections per cycle and could inject even small amounts of fuel less than 1 mg per injection. Due to the high pressure of the fuel, the outward-opening nozzle formed a stable hollow cone fuel jet in all operating conditions.

The M133 engine had on-demand multi-spark ignition and a compression ratio of 8.6:1.

Accessory belt

The poly-V belt on the crankshaft provided drive for the coolant pump, the alternator and the refrigerant compressor.

Lubrication

The M133 engine was supplied with oil by a regulated engine oil pump that was driven by the crankshaft via a chain. The valve of the engine oil pump regulated engine oil pressure and could be switched between two pressure settings of two (2) and four (4) bar by the ME-SFI control unit as required.

ECO start/stop

Compliant with EU6 emissions standards, the M133 engine also had an ECO start/stop function which enabled it to shut down when the vehicle was stationary in traffic to minimise fuel consumption.

Exhaust

The standard twin-pipe AMG sports exhaust system was equipped with an automatically controlled exhaust flap which could vary the exhaust note. The flap was adjusted by the engine control unit according to throttle input, engine load and engine speed. As an option, the AMG Performance exhaust system provided a ‘more emotive, fuller engine sound when driving under full load and when changing gears’.

Mercedes-Benz M133 engine problems

Mercedes M133 engine: turbo failure due to oil feed line contamination

In January 2015, Mercedes-Benz USA initiated Service Campaign 2014120001 for 2014-15 model year Mercedes-Benz C117 CLA 45 AMG vehicles and AustralianCar.Reviews understands that this condition also applies to the W176 A 45 AMG (since it has the same M133 engine). In these vehicles, the turbocharger may need to be replaced due to contamination of the oil feed line.

To determine if the turbocharger was to be replaced, axial play in the turbocharger would be measured by pushing the end shaft up to the end stop – by hand – in the direction of the compressor by exerting pressure on the turbine wheel shaft (exhaust side). If axial play exceeded 0.08 mm, this indicated premature wear of the turbo shaft bearings such that the turbocharger and oil feed lines were to be replaced. According to the Service Campaign, the estimated replacement rate was 25 per cent.