Just recently bought my son a 2004 x type with a 3.0 auto. The problem is a light knock that at first i thought was coming from the water pump, turns out it is not the pump but rather coming from the water pump drive stub shaft that appears to attach directly to the exhaust cam. There does not appear to be any run out on the drive pulley however you can move the pulley front to back approximately 10mm. It is almost like having alot of back lash on a gear drive, i have not taken it off but i don't think it would be gear driven. To make sure this was where the noise was coming from and not an idler bearing or the pump i took the belt off and started the car for 10 to 15 seconds, this made a major change in the noise. The noise decreases and almost dissappears at 1500 rpm. So my question is, is this a gear driven part even though it dosen't appear to be or could it be slack in the timing chain that drives the exhaust cam? Next has anyone ever relaced the chain guides and tensionors with the engine in the car? The thing that puzzels me the car is fairly low milage only 50k and it occured after an oil change could the tensior be hydralic and somehow had air enter it? Any and all help is greatly apperated. Thks Tom

 

You can rotate the pulley, it seems to have about 10mm of play from full forward untill meeting resistance to full reverse. the funny thing is it happened after an oil change. From what i can find the chain tenisoners or hydraulic so i am wondering if somehow one of them has air trapped? What you think?