Timing Chain Replacement (N20/N47)
Common in models built between 2011 and 2015 with 4-cylinder petrol (N20) or diesel (N47) engines. The plastic timing chain guides degrade and shatter, allowing the chain to jump teeth.
Affected engines: N20 (petrol), N47 (diesel), B38
What Is This Fault?
The timing chain connects the crankshaft to the camshafts, ensuring the engine's valves open and close in precise synchronisation with the pistons. Unlike the timing belts of older cars, chains are designed to last the life of the engine — but on the N20 (petrol) and N47 (diesel) four-cylinder engines, BMW used plastic composite tensioner guides that degrade under heat and oil contamination. As the guides wear and shatter, the chain develops slack. Eventually, the slack allows the chain to jump a tooth on the camshaft sprocket, throwing the valve timing out of sync. In the worst case, the chain snaps, and the pistons collide with the valves — destroying the engine instantly. This is a well-documented design flaw affecting 2011–2015 models.
Early Indications
- A metallic rattling or grinding noise from the rear of the engine on cold start, lasting a few seconds.
- A rattle that worsens over time and begins to persist after the engine is warm.
- Rough running, hesitation, or a loss of power, particularly at low RPM.
- Stored fault codes for camshaft/crankshaft synchronisation or VANOS timing deviation.
- A check engine light with timing-related codes (e.g. timing over-retarded).
- On the N47 diesel, a distinctive 'scraping' sound from the chain area at idle.
Long-Term Implications of Ignoring It
A worn timing chain that is not replaced will eventually jump teeth or snap. If the chain jumps, the valve timing is thrown out of sync and the engine runs poorly or not at all — but if the chain snaps, the pistons collide with the open valves, bending them and destroying the cylinder head, pistons, and potentially the block. This is called catastrophic interference and it means the engine is beyond economical repair. The cost of a preventative timing chain replacement is a fraction of the cost of a replacement engine. On the N20 and N47, this is not a 'wait and see' fault — the failure is progressive and the outcome of inaction is total engine destruction.
How We Remedy It
Our experienced BMW specialists begin with a diagnostic to assess chain condition — reading timing deviation values and listening for guide rattle. The replacement is a major procedure: we remove the engine's front cover, oil pan, and all associated timing components. We install a complete timing chain kit — including the primary chain, upper chain (on twin-chain engines), all plastic guides, the hydraulic tensioner, and the sprockets. We use the latest revised OEM chain guides, which use an improved composite material. The timing is set to factory specification using locking tools, the oil is changed (as metal debris from the worn chain circulates in the oil), and the engine is run and verified with live timing data.
The Benefit to Your Engine
A complete timing chain replacement with revised components eliminates the single most catastrophic failure mode on the N20 and N47 engines. It restores precise valve timing for correct combustion and power delivery, removes the cold-start rattle that signals imminent failure, and — most importantly — prevents the chain snapping and destroying the engine. With fresh oil and revised guides, the engine regains the reliability the original design lacked, and the owner is spared the multi-thousand-euro cost of a replacement engine.
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