I replaced the both belts some months ago... the other day there was a distinctive cooking smell, not garlic, more rubberish, petroleum product... not too sure of its origin, but checked for leaks, none too obvious, the transmission is not leaking, nor is the PS circuit....

So I checked the AC belt tension and there was some deflection, about 1.5cm , the Bentley recommend to recheck tension after running the engine at 1500 rpm after installation of new belts, which I did not do... I retightened the tensioner, the belt is tighter at 1 cm or less... after a 3 mile drive.

The alternator belt is a not as tight even after retightening...

Checked for glazing on the belts, none...

I checked the AC belt first because the smell was even pronounced after a 4 min drive... at some time I decided to turn off the AC... and the smell was not as strong... I could still smell it albeit a lot less and this morning drive with AC off... Will do AC on report latter.

What is the consensus on the belt deflection for the M60?

Thank you