BMW N47 Engine (2007)

The BMW N47 was an inline, four-cylinder turbo-diesel engine that replaced the M47 engine. From 2014, the N47 was progressively replaced by the B47 engine.

Crankcase

The N47 had a closed-deck, deep skirt aluminium alloy block with cast iron cylinder liners. Furthermore, the N47 had a reinforcing shell which connected the centre bearings to the skirt of the of the cylinder block. With the exception of the 85kW N47D16 engine, the crankcase had two needle-bearing balance shafts that were integrated into the crankcase.

Crankshaft, connecting rods and pistons

The N47 engine had

• A forged steel (37CrBY) crankshaft which underwent nitrocarburising for additional hardening (‘BY’ indicates controlled cooling for a homogeneous structure);
• Forged steel (C70) connecting rods which featured a trapezoidal shape for the small end. The rod caps were also separated by fracture so that machining of the cutting plane was not required; and,
• Full skirt aluminium-silicon alloy pistons. The surface of the piston skirt had a graphite coating (Graphal method) which reduced friction with the gray cast iron cylinder sleeves.

Cylinder head

The N47 engine had a light-alloy (AlSi7MgCu0.5) cylinder head which supported both camshafts in an aluminium-silicon alloy (AlSi9Cu3(Fe)) carrier. The inlet camshaft was driven by a chain from the high pressure pump of the injection system, which was itself driven by different channel from the rear of the crankshaft. The valves were actuated by roller cam followers and had Nimonic (NiCr20TiAl) valve stems.

Turbocharger

For most applications, the N47 engine had a single variable geometry turbocharger. For the 105kW and 130kW engines, maximum boost pressure was 1.5 bar and 1.55 bar, respectively.

For the 150kW and 160kW engines, however, two sequential Borg Warner turbochargers were used for two-stage turbo charging. At low engine speeds, the smaller turbocharger would operate to provide fast response. As engine speed increased, the larger, low-pressure turbocharger would gradually take over until it could provide boost pressure of 2 bar (3 bar absolute). Furthermore, the turbochargers had a wastegate valve to prevent excess boost pressure.

Injection and engine management

The N47 engine had common-rail injection which injected fuel into the combustion chamber via centrally-positioned solenoid injectors or piezo injectors. Specifically,

• N47 engines producing up to 105kW had solenoid engines operating at 1600 bar;
• N47 engines engines producing 120kW to 135kW had piezo injectors – capable of five injections per cycle – that operated at 1800 bar; and,
• N47 engines producing 150kW and 160kW also used piezo injectors, but operated at 2000 bar.

Ignition occurred via ceramic glow plugs and was controlled by the DDE7 (Digital Diesel Electronic 7) engine management system. For models with manual transmissions, the DDE7 system controlled the ECO Start-Stop system which enabled the engine to shut down when the vehicle was stationary, the transmission in neutral and the driver had released the clutch pedal. Other EfficientDynamics technologies for the N47 engine included:

• A variable output alternator (BMW’s ‘Brake Energy Regeneration);
• On-demand operation of ancillary units; and,
• A gearshift indicator light.

Emission control

To reduce the formation of nitrogen oxides (NOx), the N47 engine used exhaust gas recirculation. The N47 engine also had an oxidation catalyst and particulate filter in a common housing near the motor.

Faults: N47 timing chain failure

For 2.0-litre N47 four-cylinder turbo-diesel engines manufactured between March 2007 and March 2011, excessively sharp teeth on the crankshaft sprocket could damage, or break, the timing chain. Please note that in the event of breakage, catastrophic engine damage could result and the primary symptom of timing chain damage was a loud ticking noise from the rear end of the engine. For these engines, two situations applied:

• For models manufactured before May 2009, the timing chains, camshaft sprocket and crankshaft required replacement. Of these, the crankshaft had to be replaced because the sprocket was welded to it and the engine also had to be removed because the timing chains were positioned at the rear of the engine, Due to the cost of repair, some owners opted to replace the engine instead.
• For models manufactured from May 2009 to March 2011, the crankshaft did not require replacement since the design of the crankshaft sprockets had been changed. The timing chains and timing guides, however, still required replacement.