A small but very important issue respecting cam tensioner replacement. The spring that loads the tensioner is always replaced. This spring comes loaded in a little assembly which has the spring collapsed and under tension..
What is not apparent to some mechanics is that the spring must be "unloaded" after it is installed. There is a little holding pin on the spring assembly that must be removed.

 

The video below shows how that pin is installed and removed. I started the video right where they explain unlocking the tensioner, but the whole video is really good. The land rover in the video is using the same engine that's in the 5.0 supercharged XKRs. It gives a pretty good overview of what is involved in repairing the engine after the timing chain jumps a tooth.

 

Wow. I can't imagine a mechanic not knowing that. It is a very common type of tensioner, not a Jaguar exclusive.

 

I've often wondered why vehicle manufacturers have the chain slide over a long curved tensioner rather than using a tensioner pulley. It seems like a pulley with bearings would have less friction and be less prone to wear.

 

Because the stress on the chain is spread over a larger part of the chain rather than on a few links at a time on a pulley.