Mercedes-Benz Sprinter: OM651 Rear-Mounted Timing Chain Failure

The OM651 2.1CDI positions its timing chain at the rear of the engine at the flywheel end, an unconventional design that makes replacement exceptionally labour-intensive and often requires gearbox removal. The original chain tensioner and guide rails wear prematurely, allowing the chain to stretch and jump teeth on the camshaft sprockets, causing catastrophic valve-to-piston contact. Pre-2014 engines are disproportionately affected; independent Mercedes specialists report handling approximately one OM651 timing chain failure per week. Updated tensioner components and revised guide rails were introduced from 2014 onwards.

• Rattling or ticking noise from rear of engine on cold start
• Check engine light with camshaft or crankshaft position sensor codes
• Rough idle or engine misfires
• Engine fails to start or runs erratically after chain jumps timing

1. 1

   Start engine from cold and listen specifically for a rattling or slapping sound from the rear of the engine bay near the firewall.

2. 2

   Confirm service history for any timing chain-related work.

3. 3

   Ask when the tensioner and guide rails were last inspected or replaced.

4. 4

   If a workshop inspection is possible: Connect a diagnostic scanner and check for P0016, P0017, or camshaft-to-crankshaft correlation fault codes.

Parts involved: Timing chain.

$5,000 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 the timing chain, tensioner, or guide rails ever been replaced?”
• “Has the vehicle ever shown a rattling noise on startup or displayed engine warning lights?”
• “Is this a pre-2014 engine and has it been inspected by a Mercedes specialist?”

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.