At our shop we get our fair share of customers with BMW, Mercedes Benz, and Audi models. We started to notice a pattern failure with BMW models that have the N20 turbo 4 cylinder engine. Customers will come to Tolima’s Auto Center with misfires on all cylinders and the engine will randomly stall at idle on their BMW. The the car has no engine codes we will start diagnosing the issue by check for spark, fuel, and air. As we eliminated the possibilities that could be causing the misfires and stalling we find that the timing chain has stretched. With the chain stretched the engine goes out of time and that causes the misfires and stalling.
Cause for the BMW N20 timing chain stretch
After repairing a few of these engines we believe the reason the chain prematurely stretches is due to infrequent oil changes. BMW started recommending 10,000 mile oil change intervals which we have seen cause a series of issues once these engines go out of warranty. When a 10,000 mile oil change is recommended by BMW, people will tend to go even further over that mileage before getting around to changing the oil. As oil wears out from being run in the engine so long it loses its ability to lubricate. This loss in lubrication causes the timing chain and tensioners to wear out prematurely, particularly on the N20 engine.
Replacing a stretched timing chain on a BMW N20 engine is a laborious process, which requires special tools and knowledge to do the job right. If the job is done incorrectly and the timing chain isn’t installed properly with the engine synchronized in time the engine will continue misfiring. That is why we recommend 6,000 mile oil changes. Specially if you own a European sports sedan or coupe. If you have are experiencing random misfires and stalling on your BMW we recommend you bring it to a reputable shop like Tolima’s Auto Center.