300E Premature Belt Wear...

[JohnM.]

A couple months ago I upgraded to a larger S-class alternator (120A), new belt, new belt tensioner, ALSO replaced cracked plastic idler pulley (on bearing bracket). The belt has already developed some small stress cracks on the TOP side of the belt, very odd. They are only in a few places and 2-3" long. No pulleys are bent. Belt does not seem too tight or too loose. The only thing that changed was the alternator, and idler pulley. I have a feeling the idler pulley may be the wrong one, only because I didn't get it from my usual parts dealer. When looking at the belt with the engine off, the belt "bulges" slightly on the idler pulley; as if its too large in diameter by a bit? It seems to be pretty slow wear, its been 3000 miles / 3 months. But I would like to take care of this. What causes the TOP of the belt to crack?