I had to replace the automatic tensioner assembly on my 1998 Buick park avenue ultra which has a supercharged 3800. Do I need to take the motor mount off the passenger side to replace the belt?

You need to remove the right front tire and the plastic inner panel. After that support the motor with a floor jack being careful not to dent the oil pan. Remove the two motor mount nuts on the passenger side inner fender, you then can lowerthemotor enough to remove a stud in the motor mount to the engine, this is near the harmonic balancer. Remove the spacer behind the stud and you should be able to work the belt through there to remove and replace it. I suggest taking some pictures of the belt and pully arraignment before you remove it as it can be confusing how to put it back.i just did this and the toughest part was to get it back correctly.

I would like to Welcome both Anthony & Raymond as new Members To GMForum!
Thank You for that Valuable reply Raymond!

Feel free guys to grab a coffee and say hello and Introduce Yourselves!
You will find a bunch of friendly folks in here!
Introductions for new members - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat