Hi Ken, welcome to the forum,i only joined a week or so ago,what year is your XKR...? early XK8...XKR are timing chains,they should have been changed at 60/65,000,check your service history,Later ones 2002+ are fitted with 4th generation chains and tensioners,probably need doing at 80,000 ish,cheers Trevor.
Been into Jaguars since I was a kid (a long time now),so much so that I have owned and run my own Jaguar indie garage for over 30 years,if I can help or give anyone any advice,please just ask,Cheers Trevor.