I have searched throughout the site and did not find anything specifically about making a preventative change of the cam chains in my AJ-27 4.2L N/A engine that powers my MY08 S. I have the same engine in my MY07 XK and a very similar 4.0l in my wife's MY99 XK8. I replaced the tensioners and related goodies in my XK8 without any difficulties. That move was very fortunate as BOTH tensioners had 2mm cracks across the entire tensioner.

I replaced the old plastic tensioners with the new revised metal ones.

I believe the XK and S both have metal tensioners from the factory. I have 146,000 miles on the S and it is running perfectly. I just don't want to experience a fatal event if possible.

Does anyone know of any reference to a recommended replacement of the tensioner, cam chain and related goodies based on either age or mileage? Or, is the best practice, as long as it is working well, leave it alone?

PS: Prevention is the same reason I have replaced the filter and transmission fluid in the ZF transmissions in all 3 cars. I don't believe the transmission oil was really "lifetime" or maybe Jaguar meant the "warranty period" and not my lifetime?

 

The 4.2 litre engines have the revised primary and secondary timing chains, guides and tensioners and as such, there is little need to replace them.

The gearbox fluid and pan/filter on the 6HP26/28 ZF units should be replaced every 100,000 km (~ 60,000 miles) or five years, whichever comes first.