BMW timing chain replacement

What does a rattle on cold start actually mean?

It usually means the timing chain has stretched and the tensioner can no longer take up the slack. The noise is loudest in the first two or three seconds after a cold start, before oil pressure comes up, and it often fades once the engine warms, which is exactly why it gets ignored. The sound comes from the back of the engine rather than the front, which is the first clue that it is the chain rather than anything in the accessory drive.

A chain does not recover. It stretches further, the tensioner runs out of travel, and the timing drifts. At the point it jumps a tooth or breaks, the valves and the pistons occupy the same space, and the damage stops being a repair.

Which BMW engines are affected?

The engine in question is the N47, BMW's 2.0 litre diesel, built from March 2007 until September 2014 and replaced by the B47. It was fitted very widely, which is why the problem is so well known.

• 1 Series: E81, E82, E87, E88 and F20
• 3 Series: E90, E91, E92, E93, F30 and F31
• 5 Series: E60, E61 and F10
• X1 (E84) and X3 (E83)
• 2 Series (F22) and 4 Series (F32)

The worst affected cars were built between March 2007 and January 2009. BMW revised the design during the production run and ran a goodwill programme for a period, which it later withdrew. Later cars are better, not immune, and failures have been reported well beyond that early window. If your car is an N47, the rattle is worth investigating whatever the year.

Why is it such a big job?

Because of where BMW put the chain. On most engines the timing drive sits at the front, behind a cover you can reach with the engine in the car. On the N47 it sits at the rear, between the engine and the gearbox. There is no access to it with the car assembled, so either the engine comes out or the gearbox comes off before any of the actual chain work starts.

That is the entire reason the job carries the price it does. The chain kit itself is not the expensive part. The hours to reach it are.

What does catching it early save?

A great deal, and this is the part worth acting on. Caught while it is still a noise, it is a planned job on a running car: the chain, guides, tensioner and sprockets replaced together, and the car back in service.

Left until it jumps or breaks, the valves meet the pistons. At that point the conversation is a cylinder head or a replacement engine, and on an older car the repair can cost more than the car is worth. There is a third risk that gets overlooked: a chain that lets go at speed can stop the engine while you are driving it, which is a safety problem as much as a bill.

What we do about it

1. Confirm the diagnosis properly before quoting. A cold start rattle is the classic N47 sign, but it is not the only thing that rattles on a cold engine, and committing to a job this size on a guess serves nobody.
2. Read the car on BMW's own system. ISTA gives us the fault history, adaptation values and live data the car has recorded, not just whatever code happens to be stored today.
3. Quote before any work starts, with the chain, guides, tensioner and sprockets treated as one job rather than a part at a time.
4. Do the work, including the cars that need the engine and gearbox separated to reach the chain. It is the reason a lot of garages decline this job, and it is work we take on.

Should I just buy a different car instead?

Sometimes, and we will say so. On a high mileage car with other problems already stacking up, the honest answer is occasionally that the chain is not the only thing about to need money. We would rather tell you that before you spend it than afterwards. If the car does not need the work, we will say so.

Where are you, and can you look at it this week?

We are at Unit B2, Fram Enterprise Centre, Heol-Y-Sarn, Edwards Business Parc, CF72 8QZ, which is a few minutes from Talbot Green and Llantrisant and a straightforward run from Cardiff, Pontypridd and Bridgend. If the car is rattling on cold start, call or message us and we will get it looked at before it turns into the larger job.