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Mercedes Workshop Manual Om646 Engine ^new^ -

Mercedes-Benz OM646 engine is a 2.1-liter, 4-cylinder diesel unit widely used in models like the C-Class (W203, W204), Sprinter (W906), and Vito (W639). Comprehensive workshop manuals for this engine typically cover critical repair procedures such as timing chain replacement fuel system diagnostics detailed torque specifications for major components. Key Maintenance & Repair Procedures Official workshop documentation like the Mercedes OM646 Service Manual

(available from Shop Service Manual) outlines the following essential tasks: Standard Service

: Step-by-step guides for changing oil, oil filters, fuel filters, air filters, and cabin filters. Timing Chain

: Detailed methods for delinking and relinking the chain using specialized tools, ensuring correct timing marks are aligned. Fuel System Mercedes Workshop Manual Om646 Engine

: Comprehensive diagrams and instructions for Common Rail Diesel Injection (CDI) control units and fuel distribution lines. Mechanical Components

: Procedures for removing and installing the starter, alternator, fan shroud, and measuring cylinder bores. Essential Torque Specifications

Accurate tightening is vital for diesel engines. Technical guides such as the Mercedes-Benz Engine Torque Specifications (hosted on ) provide these common settings for the OM646: Torque Setting Cylinder Head Bolts Mercedes-Benz OM646 engine is a 2

Stage 1: 10 Nm; Stage 2-3: 20 Nm; Stages 4: 50 Nm; Stages 7-10: 90° each Connecting Rod Bearing Reassembly: 5 Nm then 25 Nm + 90° Main Bearing 60 Nm + 90° Oil Drain Plug Injector Nozzle 15 Nm + 90° + 90° (Always use new screws) Timing Chain Tensioner 80 Nm (Always renew gasket) Manual Resources & Training Guides Training Manuals : For a deeper technical overview, the Mercedes OM646/647 Engine Training Guide

provides an internal perspective on fuel and electrical systems. Specialized Reprints Bucheli Repair Manual

(found on TMB Books) is a popular choice for Sprinter II owners, covering the OM646 in detail alongside clear wiring diagrams. Digital Systems : Professional workshops often use the Mercedes WIS (Workshop Information System) Group 15 – Electrical System

Mercedes-Benz Workshop Manual: Engine OM646 (Diesel, 4-Cylinder Inline, CDI)

8. Special Tools Required (per Workshop Manual)

| Tool Number | Name | Purpose | |-------------|------|---------| | 601 589 02 21 00 | Camshaft locking plate | Timing chain replacement | | 601 589 00 40 00 | Crankshaft TDC pin | Locate TDC | | 611 589 00 63 00 | Injector puller | Remove seized injectors | | 601 589 03 63 00 | Valve spring compressor | Head reconditioning | | 601 589 00 90 00 | Harmonic balancer holder | Crank bolt removal |

Group 15 – Electrical System

  • Crankshaft position sensor (B70) gap: 0.5mm to 1.5mm.
  • Glow plug relay diagnostic (timing vs. voltage).
  • Coolant temperature sensor (B11/4) resistance curve.

Timing Procedure Summary:

  1. Rotate crankshaft to TDC Cylinder 1 (mark on vibration damper aligns with 0° on cover; flywheel pin hole accessible).
  2. Camshaft sprockets: Each has a small triangular mark. These must face each other (inward) and align with the upper edge of the cylinder head.
  3. High-pressure pump sprocket: Mark aligns with notch on pump housing.
  4. Install chain: Ensure slack is on tensioner side.
  5. Install new chain tensioner – do not release until crankshaft has been rotated 2 full turns manually.

Group 13 – Crankshaft & Lubrication

  • Oil pump chain tension check.
  • Main bearing and connecting rod bearing color codes (red, yellow, blue – they are size coded!).
  • Oil pressure specs: Minimum 0.8 bar at idle, 2.5 bar at 2,000 RPM.

1. Injector Seal Blow-By ("Black Death")

Symptoms: Chuffing noise, diesel smell in cabin, black crusty residue around injectors. What the manual dictates: You cannot just pull the injector. The manual specifies using a dedicated puller (e.g., HAZET 2780-4) and a carbon reamer to clean the bore perfectly. It also lists the exact tightening torque for the injector clamp bolts (typically 7 Nm + 90-120°). Failure to follow this leads to repeat failures or cracked cylinder heads.