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Adjusting Tensioner on Supercharged Pulley System

Hey, I’m Kevin, and welcome to Concept One Shop Talk. Today we’re going to look at the tensioner on the Supercharged Pulley System.


The first thing we’re going to do is remove the belt off the engine, and we’re going to mark this tensioner. What we’re trying to do is figure out and evaluate the travel of the tensioner. When we put the belt on there, if the tensioner is too loose, then there’s a good possibility that the tensioner will over-travel, which will bottom out and lose tension on the belt. So, we’re going to show you how to mark this thing.


What we do is lift the tensioner so there’s no tension on the tensioner—it’s all the way up. We’re going to put a mark. You can use any kind of edge or whatever you can find. There’s a casting mark right in the middle, so I’m going to mark that casting mark on the part that moves, then I’m going to mark it also on the other side that stays fixed. So now, when we pull on the tensioner all the way down, I can mark at the top. So, now you can tell how much that’s moving.


For the tensioner to move that much, that means that belt is stretching probably an inch to an inch and a half. There’s a lot of load on these belts that people don’t realize. For instance, I think this top Magnuson Supercharger, they say on an LS3, I think is around 14 pounds of boost. It takes about 80 horsepower just to turn the blower, which is pretty amazing. We don’t think about there being that much load on this belt.


Now that we’ve done that, we’re going to release the tensioner, and we’ll put a new belt on. What we figured out is, we need this belt to be actually hard to get on. I’m going to show you how to put it on and what we’re looking for.


If you look between the two, 50% of it’s going to be right in the middle. What we’ve found is we need about 60/40%. So, to be able to get a belt on it, that thing is going to come back to about 40%, and we need 60% travel to even be close to what we need.


Ok, we’re going to install the belt. What I’m going to show you is where to put these belts on. Their pretty hard—they have to be tight. Otherwise we are going to have some slipping problems. As you can see, with the tensioner all the way up, that thing’s got to go a long way. This is probably a two-man job, by the way.


Slide it on this upper idler last. If you try to slip it over these—see it’s smooth—if you try to slip it over these with a lip, you’ll never get it on there.


Ok, so we slip it on, check it, make sure everything’s where it’s supposed to be, we release. Now I want to show you something. See how close that is? You can just see how much this belt will pull when we pull on this thing by hand. A lot of times people will call and say “the belt’s hitting the tensioner”. Well let me show you something. You just pull on it like that, it’ll release and it will normally clear.


Now, what we’re going to do, is I’m going to go back to where we marked the tensioner, and you can see where we’re running right here. We’re a little more than 50%. I don’t want any less than that. If you can get one slightly shorter, that’s best. A lot of the time we are limited on belt sizes, so it’s somewhat a hit or miss. We try to furnish the belt that fits best, but if you’ve ever messed with them much, you’ll see that even the same two sizes of belts can vary in length. So pay attention to that.


We’re going to show a video of a 427 LS engine with a HeartBeat Supercharger, and I want you to watch the tensioner move as that thing goes up through the RPM range.


Thanks for watching Concept One Shop Talk—we’ll see you next time.