As a result of problematic timing chain tensioner design and other factors like engine overheating or poor maintenance, the plastic cam chain tensioners on 1997 to 2002 V8 Jaguars began to experience stress fractures, and so did some of the plastic guides. While the cars were under warranty, many tensioners were replaced by Jaguar service departments with improved components. Engines subject to this problem include XJ8/XJR engines with the last six digits of their VIN numbers between 812317 and F41862, and XK8/XKR engines with the last six digits of their VIN numbers between 001001 and A24195. In the 2002 model year Jaguar began installing upgraded plastic tensioners. These second-generation units are, to the best of our knowledge, more reliable than the early version.