OK, all done and it's running fine. I've added a few pics to help DIYers do this. It's not a bad job at all, at least on the 128 with the N52 engine. So let's get started...
This is what I ordered from ECStuning and it's everything you need for the 128, belt, tensioner and pulley...
These are the sockets you're going to need to remove the tensioner and to relieve the belt tension. You'll also need a 16mm socket to remove the pulley from underneath the alternator.
BEFORE YOU START, make sure you take a pic of how the belt is routed....
Now, just follow the steps shown in the video to relieve the belt tension and then remove the belt followed by the tensioner and the pulley. The pulley uses a steel bolt, so that could be reused, but the kit supplied a new bolt. There is also a cap that goes over the nut on the pulley. Sorry, I don't have torque specs for the pulley, so I just set it by feel and called it done.
As far as I can tell, my belt has been replaced due to one tell tale sign. You'll see that disk on the back of the pulley. The kit expressly states that disk that's retaining the bolt needs to be removed prior to installing. I remove the disk and installed the pulley and it works perfect....
I did look at my old belt and it looked to be in good shape. A sign of a failing belt is to fold it with the ribs outside. Generally you would see cracks in the ribbing. This one actually looks ok....
I found the hardest part of this install was getting the belt around the bottom side of the crank pulley. There is some sort of bolt or stub that keeps the belt from seating onto the crank pulley. You have to sorta slide the belt in sideways at the bottom to get it to seat. Once that was on properly, the rest of the belt fit fine. Also as noted in the video, the easiest place to put final loop of the belt on was on the tensioner pulley.
The video calls for ~18ft/lb of torque followed by a 90degree turn. I do some basic woodworking and I happened to have a large builders square. This was perfect for dialing in the last part of the torque sequence. Just pulled the ratchet from one leg to the other. Done....
All in all, I spent about 1.5 hours doing this job carefully. Like I said, it's not hard and basic hand tools and a torque wrench are all you need. It would be best if you had a either an inch/pound or zero start read on your torque wrench. Mine started at 20ft/lb, so I backed off doing the final 90degree torque.
So that's basically it ladies and gents. Hope this write up helps...