FAQ: Upgrading Serpentine Belts & Pulleys?

At some point you are going to want to change your OEM drive belts to a higher performance type. This might be when you notice cracking or glazing of the existing belts, or maybe you decide to upgrade just for the sake of not having to worry about it later on. Whatever the case, Gates makes some very high-quality belts that can be purchased through NAPA auto parts stores. Both SC and accessory belts can be had together for around $60.

Changing belts on the Riviera is a chore due to the required removal of a motor mount and the loosening of a large bracket on the side of the engine. You can pay to have this done, or you cab try to tackle it yourself. Due to the time/money required to change the belts, it is recommended that you do both at the same time.

After adding a smaller SC pulley, you may be wondering if a smaller SC belt is needed. The short answer is no, but it may be a good idea to increase the diameter of the SC tensioner pulley to 3.5" to tighten things up when running a 3.4" SC pulley. GM makes a 3.5" tensioner pulley that sells for about $20. Additionally, going smaller than a 3.4" SC pulley requires using a 3.5" SC idler pulley as well. This is to ensure the SC does not rub against itself near the tensioner. Here are the rules:

-OEM SC belt works with OEM 3.8" SC pulley - keep tensioner and idler pulleys stock.

-OEM SC belt works with 3.6" and 3.5" SC pulleys - keep tensioner and idler pulleys stock.

-OEM SC belt works with 3.4" SC pulley - can keep stock tensioner pulley, or change to optional 3.5" - keep idler pulley stock.

-OEM SC belt works with 3.3" SC pulley - must change tensioner pulley to 3.5" - can keep stock idler pulley, or change to optional 3.5".

-OEM SC belt works with 3.2" SC pulley - must change both tensioner & idler pulleys to 3.5".

-OEM SC belt works with 3.1" SC pulley - must change both tensioner & idler pulleys to 3.5".

-using 3.0" or smaller SC pulleys will probably require a smaller SC belt size.


If your car has 85k miles or more, it is a good idea to change all of the idler and tensioner pulleys on both the accessory and SC belts. There are 5 pulleys total that run about $100 for all.

Changing the pulleys and belts does not give that much of a performance advantage, but it gives you the added assurance that belt slippage will not occur, and that nothing will break as you continue to extract more power from the engine. As some of us have discovered from experience, it's no fun to be stranded along side the road due to the failure of these parts.

Thanks.........This was very helpful........i checked under my hood and my belts look and feel strong and theres no fraying or stripping of the belts so i should be good for some time!

If I remember right you only have one belt? Correct? If you got some miles on your Riv look into changing some pulleys out.

If going to a smaller SC pulley:

Replace right hand #3 pulley with dayco part # 89006, a 3.5" smooth metal unit. Disregard part# 89007, that is stock 3".

Makes a notable difference in picking up the slack.

When changing your pulleys:

pulley # 8: replace with dayco p/n 89051 (metal).

The gates part # is 38009 (plastic) and Dayco plastic part number is 89009.
I strongly recommend the metal replacement mentionned above.


pulley #9 : If you plan on having the engine mount off, take the time
to change pulley #9 for # 89006. I did this when I did the cam.
Hopefully I'll never have to go there again since it's metal.
Note: It has been reported that pulley 89006 may not fit on the 1996 riviera when used as a replacement for the lower supercharger idler pulley (9). NAPA part 38007 is known to fit on the 96.


NOTE: All parts on pic are metal EXCEPT pulley #8 (89009). Use metal number is 89051.

Running down to 3.5" SC pulleys will work fine keeping the belt and tensioner pulley (#3) stock. Using 3.4" SC pulley will work with stock tensioner pulley, but 3.5" is recommended. Smaller than 3.4" SC pulley requires 3.5" tensioner pulley (see top post).

In my experience, have never seen a pulley break because it was made of plastic (on my engine). Metal is fine, but is heavier. In my case(s) It was the bearing that failed, causing the pulley to frag. I use a plastic idler pulley (#8) with no issues. With 3.3" SC pulleys and smaller, it's a good idea to use a 3.5" idler pulley in place of the 3" stock size.

If your belts slip a little, is it something that you will definitely notice happening (noise,power loss, etc) or not necessarily?

Although the metal ones are heavier, the OEM plastic ones are of inferior quality. I would not hesitate to buy the gates replacement plastic pulleys as they feature improved bearing design.

quote: "If your belts slip a little, is it something that you will definitely notice happening (noise,power loss, etc) or not necessarily?"

My first clue was the sound I heard when I let off the throttle at high RPM. The "squeak-squeak" went away when I installed the 3.5" tensioner pulley. My scans showed slightly higher boost after the new tensioner pulley, but I'm still not sure if that was the only factor. In my case, any improvement was minor, but it was only $20.

The ones who run into problems are the W-Body cars, which have a different SC belt route that doesn't have as much contact with the SC pulley as our Rivs do. When going below a 3.4" SC pulley, they can see severe slip in the upper RPMs, easily diagnosed by a sharp drop in boost (and power) while RPM continues to climb.

I'm currently using a 3.4" s/c pulley and just switched from stock 3.0" tensioner pulley size to the 3.5". Just for the record, I had absolutely no problem at all with slipping or anything with the stock tensioner pulley, with the old belt or new one. Now the clearance of the belt riding the top of the tensioner pulley and the belt section thats above it (going from the s/c pulley to forward idler pulley) is uncomfortably close. I have run the engine and it doesn't touch or anything but i can merely flick it with my finger and make it rub.

At this point I really want to get the larger idler pulley to bring that top belt section higher and a 3.3" or 3.2" for the s/c for winter anyway

According to the guide, the 3.5" tensioner pulley is necessary to use the 3.3" s/c pulley but having that s/c would make the clearance issue i'm worried about with the 3.4" even closer

Overall, it seems like it would make more sense to suggest a larger idler pulley first to keep favorable belt clearances.

Those who has swapped around in the 3.2-3.3 s/c pulley range, what's your input?

I put on a 1 inch shorter belt. It's just right for 3.5 to 3.2 pullies. It's a real PITA to change the belt, but I needed it at the time so it was convenient.

quote: "I have run the engine and it doesn't touch or anything but i can merely flick it with my finger and make it rub."

Even though it's close, it shouldn't be a problem. I ran a Gates SC belt with 3.4" SC pulley for 90k miles, more than 80k of it with a 3.5" tensioner pulley. The reason for the tight clearance is better surface contact around the SC pulley. The closer the better, imo. Keep in mind, when you are at WOT, the belt's rotating mass should throw it out away from it's position at idle, so it will form a slight curve, ensuring no direct contact.

Of course, the condition of your tensioner and the exact length of your belt can make a difference. If you are uncomfortable with how it looks, add the 3.5" idler pulley. I think I paid $8 for mine.

I know i saw this somewhere but i cant find where
what is the part number for the 3.5" idler pulley?
Aaron, where did you get it for $8 that's cheap!

Autozone. Take your stock idler off when you get there, compare to their pulleys behind the counter. They won't be able to pull it up on the computer.

the autozone by me didn't seem to have it.
Anybody know a part number for it?

Mine didn't seem to have it either until I asked to see various pulleys. I'll try to find the part number, but I might not have it anymore

It seems that murrays, autozone, and napa around me didn't have this size pulley in stock and wasn't too sure about which to order. The catalogs just aren't very custom friendly

I decided to go the questionable / free way and took the 4+ inch pulley from work to use for the forward idler and have my stock tensioner pulley set up with a 3.2" s/c pulley

I'll take a pic of this setup some time today probably but the belt wrap around the supercharger pulley is lower but I have no problem at all. No noise, no slip, nothing. The belt is the gaterback I got a couple months ago. The only thing im not sure about is if the tensioner is out of position.

that's where the tensioner sits as it is now. Is that little notch i barely see the indicator?

Which way is that pulley #8 threaded? AKA the huge ass pulley pictured in the post above.

#8 and both #3s are reversed thread direction.

yea they were both a beeotch to break loose the first time. #8 I ended up getting it broken loose with nothing short of a half in breaker bar to the torx socket. the cheap torx socket i had snapped.

Were you ever to get that part number for the 3.5" ribbed idler AA? mine are really close. like i can only fit my pinky in there.

Sorry, I haven't. Will try to find out for you next time I'm at the local AutoZone.

thanks!

I took some pics of the belts and pullies of the wifes 99 Riv, they look fine to me but I would like to get youse guys opinions.
The car has 77,500 miles, I noticed they are GM belts but I dont know if they are original or have been changed.
Thanks for any tips or observations.




Bert

another pic