Thread: How much tension should supercharger belt have?

Car is new to me. While trying to diagnose power loss / misfiring / shuddering under boost, I noticed the supercharger belt can be pushed down quite easily, at least 1.5" to 2", to the point it touches the tensioner pulley. Wondering if that is normal, or if the tensioner is going bad.

Thanks.

Hard to see the lines in the pic, but mine looks sort of like this.

____V_______
|____|__|__|

To be clear: I'm talking about the belt that goes over the pulley on the snout of the supercharger, and the tensioner the belt goes around.

Originally Posted by BillBoost37

So what's that mean. The picture has words and is pretty self explanatory. Is your belt stretched? is it too long?

I assume the diagram you posted is generic to show how tensioners have markings, because it doesn't appear to be the exact tensioner I'm talking about.

I've added an edited version of mine where I drew black lines over the arrow and markings.

The "arrow" is between the two wider spaced markings on the left. If I push down on the belt to simulate a shorter belt, the arrow moves right. So I assume the lines on the right side indicate optimal length, and mine is in the "replace soon" range.

But still, I don't know how stiff the tensioner should feel. I can push down on the belt quite easily, probably could get the belt off without a tool. Not as stiff as other tensioners I've worked with on other cars, so I don't know if it's normal for this one. Maybe it just feels weak because the belt is stretched and it's not in it's optimal position.

Looking for a good service manual. Anything better than Haynes/Chiltons?

Originally Posted by wmorrison65

Car is new to me. While trying to diagnose power loss / misfiring / shuddering under boost,

Took my coil packs off last night. A couple terminals were covered with corrosion. Cleaned them all up with some steel wool. Tested them with a multimeter, all similar resistance.

New plugs and wires today seem to have cleared up the problem. Planned to do it myself but because of snow and being busy with plumbing, I just had a shop do it.

The gap on the old plugs was so wide, I'll bet they were the originals.

Originally Posted by wmorrison65

I noticed the supercharger belt can be pushed down quite easily, at least 1.5" to 2", to the point it touches the tensioner pulley. Wondering if that is normal, or if the tensioner is going bad.

The shop said the tensioner was bad. I've got a new belt and an OE tensioner on order. I REALLY hope today was the last snow of the season. I've got brakes and struts to change on my other car.

Man you guys are hardcore on the help. Why can't you just answer the guys question without being an ass?

Belt tension should be checked several ways.

#1 all belts stretch bar none.

#2 the lines on the guide for the tensioner are just that, only a guide. They only indicate position of the tensioner relative to belt length and nothing more.

#3 springs wear out, so regardless of the pointer position if the spring is worn the belt will slip.

If you think you have a worn out tensioner pressing on the belt like the OP did is a good way to tell if there is enough tension. It should be higher tension than the regular serpentine belt. Superchargers require a substantial amount of power to run at full tilt. On the Tbird SC it was about 60HP, for the GM cars it's probably in the range of 40hp. It would be nice to see some decent posts instead of some guys being keyboard warriors. I thought the purpose of these forums was to help one and other.

Jeff

I guess I just read it as a little rude when there is more to go with a bad tensioner than the indicator. I've replaced lots of stretched belts with weak springs that were checked by mechanics as needing various replacement parts just because they told the customer that the belt was in range.

Guess I was a little too sensitive.

Jeff

Belt stretch and a bad spring can keep the indicator in the good range. Even a new belt and bad tensioner can show good on the indicator.

The OP discovered that he had a bad spring at his mechanic.

Like I said may have been a little sensitive about the matter.

Lol, on my Tbird we had a jack shaft so you had one step up in speed between the crank and JS and another between the JS and SC. So there were 2 tensioners. Usually you could tell when it was time to check was when it looked like someone put pepper on the sc snout. Or you could watch the boost gauge go to 13 then drop to about 8 then pick back up.

Jeff