Whether you drive a 3-series equipped with the smooth straight-six or an 850 with a V12, your car's engine is nothing without a BMW timing chain or BMW timing belt. Different engines use different methods of driving the camshaft, which is essentially the difference between a BMW timing chain and a BMW timing belt: One is a chain and the other is a rubber belt. There are pros and cons to both the BMW timing chain and the BMW timing belt. For example, a BMW timing chain is extremely reliable and long-lived, succumbing only to wear and stretch over time. The BMW timing chain can easily last over 100,000 miles, but when your engine begins to show sluggish response and poor tuning despite the good condition of other systems, the BMW timing chain is suspect. However, a BMW timing chain tends to be noisier and more complex in the overhead-cam architecture favored by BMW. Noise and complexity, or the lack thereof, are the two main advantages of the BMW timing belt. Due to its construction, the BMW timing belt is relatively immune to stretching and wear also. Unfortunately, when a BMW timing belt does fail, it generally fails in catastrophic fashion. A broken BMW timing belt can lead to the engine simply not running, or it can lead to an engine rebuild, depending upon the engine design. That's why the BMW timing belt requires periodic replacement whereas the BMW timing chain is considered a 'lifetime' component. Consult your BMW repair manual to find out what type of component your engine uses: the BMW timing chain or the BMW timing belt. If you have a BMW timing belt, be sure to follow the recommended replacement schedule provided by the manufacturer. After all, BMW engines are things of beauty, but replacing one isn't cheap!