Mercedes-Benz C-Class: OM651 Rear-Mounted Timing Chain and Oil Pump Chain Failure

The OM651 2.1-litre four-cylinder diesel engine is uniquely engineered with the primary timing chain mounted at the rear of the engine, adjacent to the flywheel and transmission bellhousing. Unlike conventional front-chain layouts, replacement requires either full engine extraction or transmission removal, making the job extraordinarily labour-intensive. A secondary oil pump drive chain at the front of the engine is also prone to stretch. Both failures have been extensively documented across C220 CDI and C250 CDI variants in W204 and early W205. Oil pump chain failure in particular can result in sudden loss of oil pressure and bearing damage within seconds.

• Metallic rattling on cold start from engine bay
• Check Engine or EML warning light active
• Rough idle or low-speed vibration
• Oil pressure warning light (oil pump chain failure)

1. 1

   Request full service history for any timing chain or oil pump chain work.

2. 2

   Cold-start the engine and listen for rattle before oil pressure builds.

3. 3

   Check for any oil leaks at the front of the engine.

4. 4

   Ask for any dealer or independent inspection reports mentioning chain condition.

5. 5

   High-mileage examples (over 150,000 km) without documented chain work carry elevated risk.

Parts involved: Timing chain.

$5,500 to $12,000 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has timing chain or oil pump chain work been carried out?”
• “What is the full service history and mileage at each service?”
• “Has the vehicle ever shown an oil pressure or engine warning light?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.