A genuine workshop manual is not an expense; it is an investment that pays for itself on the first injector seal repair or timing chain inspection. Whether you buy access to Mercedes WIS ($10–20 for 24-hour access) or purchase a third-party hardcopy, ensure you have the exact procedures for your specific OM646 variant (e.g., OM646.963 vs OM646.961—the ECU and injection systems differ).

A distinct rattling noise on cold starts lasting 2–5 seconds indicates a failing hydraulic chain tensioner or chain elongation.

Stage 1: 30 Nm | Stage 2: 60 Nm | Stage 3: +90° | Stage 4: +90° 30 Nm + 90° Main Crankshaft Bearings 55 Nm + 90° Camshaft Bearing Caps Fuel Injector Hold-Down Bolt 7 Nm + 90° + 90° (Always use new stretch bolts) Engine Oil Capacity

Proper adherence to these manual procedures ensures that the rugged OM646 diesel engine can easily surpass 500,000 kilometers of reliable service.