On the early model years the timing chain of the B47 stretches faster than intended. The chain tensioner compensates for the stretch for a while and then no longer can: the chain jumps, the valve timing goes off, and in a severe case engine damage follows. The first sign is a rattling, clacking noise on a cold start that goes quiet after one to three seconds. On the B47 the chain sits at the front of the engine, not at the rear as on its predecessor, the N47. The replacement is therefore considerably less, between 1,200 and 1,800 euro, against 2,000 to 2,500 euro on the N47; if the chain has already jumped, the repair can run up to 4,500 euro. The risk is highest on units built before the end of 2015, with a reported rate of 3 to 5 per cent. 2016 was better but cases remained, and between July and December 2016 an improved chain tensioner was phased in. After mid-2016 the problem is rare, below one per cent. The engine has been in almost every four-cylinder diesel BMW since 2014, from the 1 Series to the 5 Series and from the X1 to the X4. The build date therefore says more here than the model.
What to check
- Start the engine cold and listen for the rattling noise in the first seconds
- Ask for the build date, because units built before the end of 2015 are the risky ones
- Ask whether the chain or the tensioner has been replaced, and ask for the invoice