I have just purchased an XK8 97 model 100k miles. On inspection engine fine no knocks etc but on delivery a loud tappet sound.
returned to dealer who was told to drive it for 10 miles at 2500 rpm and the tapping has gone. As (if I am right) it does NOT have hydraulic tappets I can only conclude that it was a sticking valve.
I am concerned that if the valve sticks again and gets hit by the piston I will be in big trouble.
Clearly a lot of hassle to reject the car .
Any comments to help me?

 

The valvetrain in the AJ V8s is what they call direct acting mechanical bucket and you are correct that there is nothing hydraulic about it. Given the design, it is very unlikely that a valve is "sticking" unless the engine has been seriously overheated and dropped a seat or a valve is already bent.

If the care runs properly, i.e. not rough or with misfires or excessive P codes then it probably is not something to do with the vales that you are hearing. Fuel injectors can have a tick to them, some can be quite noisy. The cam phasors can also get to making noise.

If you don't know the history of the car, you might do a couple of oil changes in a short duration just to make sure everything is flushed out and clean. For the injectors, based on some advice here on the forum I've taken to running a couple ounces of TCW3 oil in each tank of gas and that has made a notable difference in the injector noise.

 

Very helpful the garage has done a flush and oil change but as I only had the car for 6 hrs I was not going to get into full test mode or do any dismantle in case it was a send the car back senario