I have a 2004 gasoline VR6 engined Touareg in my work shop. A compression check shows normal on the even numbered cylinders but a low 85 psi on all the odd numbered cylinders. ie 1,3,5. This seems strange on an engine with a common cylinder head for both banks and with single separate exhaust and inlet cams. Can anyone come up with a reason for this coincidence, other than damaged valves? I suspect that the engine may have been overheated in the past. I hear a slight timing chain rattle sometimes when revving the engine.