I have a 1991 300SE. When I bough the car back in March it had a 'chatter' that would last for a few seconds at a cold start that I new about. The owner believed that it was the smog pump.

When I replaced the smog pump I replaced the belt as well. I did not know how the tensioner on this worked. I thought that it was like any other spring loaded tensioner. I slipped the belt on going in order as the manual instructs. The belt seemed snug as I was expecting.

Since replacing the pump the noise has not gone away. Next I suspected the engine mounts. The passenger side was collapsed and the driver's seemed OK, but I went ahead and replaced both. No difference.

Now it has the chatter at a cold start at a bad noise at idle that makes the hood shake. If you bring it just off of idle it stops. With the engine running at I have pushed against the top end of the tensioner dampener. Doing this seems to reduced the noise about 90%.

I began searching and reading about the tensioner and found this thread. I went and check my belt. It is loose!!. I loosened the 19mm bolt ahd tried the jack screw....the @#$%@#% tension does not seem to move. I removed the belt to find that by hand I can removed the tensioner a few degrees, but aside from that it seems frozen. I have removed the 19mm bolt and the thing will not budge. How much of this f@#king car do I have to tear down to see and get to this tensioner. It is looking like I need to remove the PS pump and the pulley from the water pump, correct? Sould I plan on removing the radiator as well? You can not see anything in this area on this engine.

Hydronuclear, you are soooooo correct about the 'design' of this. It is from hell. So far I just have the fan, tensioner bolts, and air cleaner assembly removed. Two weeks ago I replaced the water pump on my 1997 5.7L Silverado is less time than I have invested in this job so far.