I was considering getting an underdrive pulley to get a few more horsepower, and asked on the V6 J-body list about them. List members told me that ASP Racing makes an underdrive pulley for my Z24.
The old pulley is also the engine's harmonic balancer. The new pulley is just that -- a pulley. This mod eliminates the harmonic balancer. The V6/60 is a true even-fire engine (120 degrees between firing events), is internally balanced, and has the "proper" cylinder bank spacing (360 degrees / 6 cylinders = 60 degrees). The crank is fairly short and has large main bearings compared to other engines like a small-block Chevy, so running without a balancer should be fine. ASP Racing claims that the belt drive removes crank harmonics, and that this pulley is fine for the street. I'm fine with this arrangement, but I thought this is information that is good to have before making the decision to purchase the pulley.
The website listed one for a '91-'93 Baretta 3.1V6 for $119.95 plus $5 shipping, so I called and ordered one. Shipping was pretty fast, and it looked like a quality part. Time to install it.
Parts needed:
Tools needed to install:
Supplies to have on hand:
I mention ratchet and extension often, but I only needed a 1/4" and 3/8" ratchet, and two extensions (one each).
The installation is fairly easy. First disconnect the battery, put the car on jackstands, and remove the passenger side wheel. Set the emergency brake and chock the wheels.
There are 2 10mm bolts and several 7mm screws that retain the splash shield over the pulley. You do not have to remove the whole inner fender or the bumper cover -- just the splash shield. A bit of inspection will make it obvious what part needs to come out. Once that is out, you can see the crank pulley.
Now you need to remove the belt. There is a cover over the belt on the water pump, retained by a 10mm bolt on the side and two 10mm studs on top. Remove these fasteners and the cover. Using either your breaker bar or belt tensioning tool, rotate the belt tensioner back away from the belt and remove the belt.
Now it's time to remove the old pulley. First remove the center bolt (15mm socket). An impact wrench helps here but is not required. Install the harmonic balancer puller using your 2" bolts. 3/8" fit mine, but I think a previous mechanic screwed up the threads. I really suspect that they are 10mmx1.5 bolts. Find what fits your car, and use the shortest bolts that you can that also thread completely into the balancer (but don't stick out of the other side!). Then, start tightening the center pull bolt on the puller until the balancer comes off.
Once you have the old balancer off, inspect the crankshaft for problems, and inspect the oil seal at the block. Now is a good time to see if you have any oil leaks that need your attention. Clean the crankshaft and the surrounding area. Also clean the center bolt and washer.
Here is a picture of the old balancer next to the new one:
The old balancer weighed in at almost 5 pounds on the bathroom scale, and the new one weighs in at about 1 pound. The old pulley was 18.5" around, and the new one is 15 11/16" which is the 15% reduction they claim.
If the keyway came out, clean it up, put a dab of RTV on it, and reinstall it in the crankshaft. Place a light film of oil on the inside of the new balancer and on the crankshaft itself. Now, carefully place the new balancer on the crankshaft, and reinstall the center bolt and washer. Tighten the bolt slowly to press the new pulley onto the crankshaft.
Once you have the new pulley seated, loosen the bolt, and retorque it to 100 ft-lbs. I did this in a few steps. First I torqued it to 20 ft-lbs. Then I torqued it to 60 ft-lbs., followed by 80 ft-lbs. and then 100 ft-lbs. To hold the pulley I threaded 2 3/8" bolts into the balancer and used my lug wrench wedged between them to hold the pulley while I torqued the center bolt.
Now install your new belt, paying attention to the routing diagram. I found it easiest to place the belt over all pulleys (including the tensioner) except the crank pulley. Then use your breaker bar or tensioning tool to move the tensioner back while you slip the belt on the crank pulley. This is easiest to do if you're under the car.
Now reinstall the splash shield, the cover on the water pump, and the wheel. Take it off the jackstands, reconnect the battery, and shut the hood to the safety latch. Start the car, and listen for any squealing or noise that would indicate belt/pulley alignment problems or parts rubbing the pulleys or belt. NEVER STAND NEAR THE CAR WHEN YOU FIRST START IT in case there is a problem and it throws the belt or the pulley!
That's it, you're done! I'm happy enough with this mod that I would do it again.
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