So my new engine has an aluminum main pulley, its the one with the multiple timing marks on it. It seems that its a smaller pulley so i can not get enough tension on the alternator belt because belt it self it too long. Any one ever ran into this problem. What belt do i get or am i gonna have to go to Auto zone. and try to find a smaller belt by eye. Thanks for the help guys

 

Yep, experienced this. Look for a 300 length belt. That means it's 30 inches long. Look for a 13 width, however stores around here don't sell 13 anymore so I'm stuck with 15 width. It works, but you gotta retension after the sheave wears the belt down a little. Avoid 17 width.