Write-Up: Replacing Belt Tensioner Pulley (Series I)

Abaddon wrote:

As long as it's tight, and you don't reef it down like Hercules, I don't see why it matters what the exact spec is. It's not like you're installing Intake or Head bolts....  

Understood, but I don't want it to be too loose and back out or allow any off-axis wobble. Also of course don't want to overtighten and strip something, or in my past experience bind one of the pulleys.

...just don't want to revisit this repair a few months down the line just because it was over/under tightened. So I was just checking.

Thanks,
Al

OK, replaced the tensioners, idlers and installed the new "HD" Gates belts today. Pretty straightforward.

The two tensioners are indeed held on with bolts through the center from the front (1/2" bolts), so you can remove and install them individually without removing the bracket that all of these accessories mount to. The lower tensioner is a bit a trick to unmount unless you remove its pulley as its bolt is directly facing the frame so any ratchet is a tight fit.

I torqued them to ~35 ft/lb (service manual indicated 37).

I torqued the stacked idler bolt to 15 ft/lb although there is no spec I could find for the Buick, but around 14-15 seems the norm on other manufacturers. That felt "tight". If someone has a better known correct value for the stacked idlers bolt torque, that would be great to know.

One of the Pontiac guys has a write up that seems to confirm the 37 ft/lb for mounting the tensioners, but also says 37 for the idler bolt. That seems high to me for the Series I stacked idlers, but.... not sure.

http://www.paulstravelpictures.com/GM-Pontiac-Grand-Prix-Idler-and-Tensioner-Pulley-Replacement-Guide/

Al, I haven't been able to track down any solid numbers for the idler pulleys as far as torque specs. I'll be doing mine either tomorrow or Wednesday. Will keep looking but if no luck I'll try 15ft lbs like you did as that's what I've seen most often.
I was curious though about the specs on the tensioners. You indicate 37ft lbs? Is that the assembly or the pulley? Couldn't be the pulley could it?

llamalor2112 wrote:

Al, I haven't been able to track down any solid numbers for the idler pulleys as far as torque specs. I'll be doing mine either tomorrow or Wednesday. Will keep looking but if no luck I'll try 15ft lbs like you did as that's what I've seen most often.
I was curious though about the specs on the tensioners. You indicate 37ft lbs? Is that the assembly or the pulley? Couldn't be the pulley could it?

 
The FSM says something "tensioner mounting bolt" = 37 ft/lbs

Along with that, I've noticed that if one tightens the "pulley bolt" more than around 15 ft/lbs, the bearings get loaded and the pulley will start to drag, esp on the tensioners, causing it to jump. So I dunno.
 
I am going by the dealer today or tomorrow and will ask them if they are willing to look up the actual pulley mount bolts, both tensioner and idler.

This is series 2 info....

Belt idler pulley bracket bolt 22 ft/lbs
Belt Idler Pulley Bolt (VIN 1) 37 ft/lbs
Drive Belt Tensioner Bolt 37 ft/lbs
Drive Belt Tensioner Bracket Bolt (VIN 1) 37 ft/lbs

BUT you say that the idlers start to bind past 15 ft/lbs....

Robo or the dynamic Dave duo have any info on this?

The pulley bolt itself is a special bolt that mates up a shoulder with the inner bearing race. If you overtighten it, you still shouldn't be able to expand that race. Use of the incorrect bolt, however, could cause it to be tightening on the wrong spot causing binding.

IMO you don't want to overtighten it because you are threading into aluminum. But the pulley should be unaffected (unless you really really REALLLLLY overtighten)