Underdrive Pulley

In October of 1999 I had an Unorthodox Racing Underdrive Crankshaft Pulley (UDP) installed on my 1999 Maxima SE Automatic. I purchased the UDP from Steve Millen Sports Parts (Stillen) for $175 and had it professionally installed directly by the manufacturer, Unorthodox Racing, in West Babylon, NY. The UDP is an aftermarket replacement for the crankshaft pulley on the Maxima, which drives the accessory belts. The UDP replaces the stock crankshaft pulley with a smaller diameter and lighter weight unit which allows the engine to rev more easily. Basically, an "under" drive pulley is any replacement pulley which is smaller in diameter than the pulley it replaces. The principle behind the aftermarket part is that the smaller diameter pulley has a lower "tangential" velocity than the stock pulley given a constant engine RPM. This means that with the aftermarket pulley, less energy is used to drive the accessories, and hence more power is available at the front wheels. The result is a noticeable increase in horsepower (about 8 hp for the Maxima). There is still plenty of energy available to drive the accessories, so installing the UDP will not in any way effect your ability to run the A/C at full blast while the front and rear defoggers are on and you have the factory BOSE system cranked up to the max.

For anyone out there who rides a 10-speed bicycle, you are all familiar with the front and rear chain rings, right? Well, you can think of the crankshaft pulley on the Maxima as analogous to the front chain ring on a bicycle (the part where the pedals are attached). When you downshift the front derailleur from the larger chain ring to the smaller chain ring, the bike suddenly becomes much easier to pedal. This is exactly what we are doing by replacing the stock pulley on the Maxima with the smaller diameter aftermarket UDP. We are making the car "easier to pedal".

I'll tell you right off, if your car is an automatic transmission model, I highly recommend taking it to a qualified mechanic and having a professional do this mod. On the auto model, this is not an easy job. For the 5-speed car, adding the UDP is within the realm of a qualified amateur. I will try to outline the steps necessary for the UDP replacement for both models, and make specific note where there are differences due to the manual / auto transmission. I lucked out, as Unorthodox Racing, manufacturer of the Maxima underdrive pulley just happens to be a few towns away from me in West Babylon, NY. The owner, Shawn, is an extremely nice and accommodating guy, and was happy to do the install himself in his own shop. Not only that, but I was able to watch the entire process and take the digital photos you see here. Cost of the labor was 1.5 hours (translated into $75.00), which I had no problem spending not to have to do this job myself. A mechanic's lift and air tools make all the difference.

CONCLUSIONS:

After driving the car around with the UDP I can tell you a few things:

1. There is absolutely no difference in noise output or drivability of the car.

2. Acceleration is noticeably improved throughout the power band, with most gains coming in low-end torque and 0-60 times. Yes, you WILL feel the difference. This is not one of those "un-noticeable" mods. The 5-speed car will pick up an even more noticeable improvement than my automatic did.

3. All accessories work just as well as before. No discernible difference AT ALL in A/C strength, power steering capability or electrical output.

	Step 1 - Remove the stock pulley This is the hard part. If you can get past this, you're home free. First jack up the passenger side of the car and remove the front wheel and oil cover. This will expose the crankshaft pulley. You will need to loosen the bolt that holds the pulley to the engine. The bolt was 19 mm on my car. When you try to loosen the bolt, the entire pulley (and all accessories) will rotate counterclockwise - you need to stop this from happening or you will not be able to get the bolt off. With the 5-speed car, all you need to do is have an assistant get in the car, put it in 5th gear and hold the brake pedal. Then you can get under the car, get the 19 mm socket on the crank pulley and YANK for all you're worth, being careful not to give yourself a hernia (I've had two myself). If you have air tools you can get this bolt off easily without having to lock the flywheel (regardless of manual or auto trans), but you will eventually need to lock the flywheel in order to torque the bolt down after the new pulley is on. If you do not have air tools, and your car is an automatic transmission model like mine, you do need to lock the flywheel in place while the bolt is being loosened. On the '99 Maxima there is a small access port just to the driver's side of the huge steel support bar which runs down the middle of the engine underneath the car. The access port has a cover plate which is held in place with two small easily removed bolts. Removing the small bolts will expose the flywheel. We used a piece of hardened steel (a chisel bit) to stick in between the flywheel and the housing cover being very careful not to damage the flywheel teeth. If your car does not have the access port, it will be necessary to remove the starter motor to gain access to the flywheel. If you have the shop manual for the car, the access port is documented in the section on removing the timing chain, and in the section on removing the oil pan. Nissan calls it simply a "rear cover plate". It was not necessary to remove the starter on my car, but I do not know if all 4th generation Maximas have this access port. It was clearly put in place by the Nissan engineers with the express purpose of allowing access to the flywheel. Check your vehicle. Anyway - thanks Nissan for putting it there.
	Step 2 - Remove the drive belts Once the pulley bolt is loose, go about the normal procedure for removing both drive belts. To summarize, remove the large belt by loosening the idler pulley bolt and then loosening the upper bolt to raise the idler pulley. Next, lower the power steering pump and remove the smaller belt. This procedure is also outlined very well in the shop manual. This was not easy, even for Shawn, which is why I recommend a pro for this job. The difficulty is in the placement of the bolts for the power steering pump, which are difficult to reach. Small hands, a universal, and a LIFT make this a lot easier.
	Step 3 - Remove the stock crank pulley Remove the stock crank pulley. My car was almost brand new so the pulley slid right off the spline without the need for a gear puller. If your car is older, the pulley might be a little more stubborn and require the use of a gear pulley. A good gear puller is an invaluable tool anyway and is available for about $25.00 from almost any automotive store or from a Sears hardware store.
	Step 4 - Replace the front oil seal The shop manual recommends replacing the front oil seal any time the crank pulley is removed. This may or may not be overkill, but considering that the rubber oil seal is only $6.50 from a Nissan Dealer (part # 13510-31U00) you might as well do it. Simply stick a flat bladed screwdriver in there and pop the oil seal out. Coat the new oil seal with motor oil and pop/tap it back in place. Real easy.
	Step 5 - Install the new pulley Coat the inside bore of the new pulley with anti-seize compound and then slide it onto the engine. The UDP is keyed so you can only stick it on one way. Snug the bolt down but do not torque it yet. According to Shawn, the primary purpose of the anti-seize compound is to limit the contact of the aluminum pulley with the steel crankshaft spline. Something about dissimilar metals not "liking" each other. One thing I noticed immediately was the weight difference between the stock pulley and the Unorthodox Racing pulley. The stock pulley weighs in at a whopping 5 pounds! I didn't get a chance to weigh the UDP, so I don't have a number but I can tell you that it is made from lightweight aluminum and weighs MUCH less than the stock part.
	Step 6 - Replace the belts Since the new pulley is smaller than the stock pulley you will need to get new shorter length belts. You cannot reuse the stock belts. I went to a local US-1 auto parts store and bought the exact belts recommended by Unorthodox. They are Gates belts, numbers K-060408 and K-040292. I tried Pep Boys and Auto Barn, but neither of those stores carried Gates belts. The price of both belts together was $31.44. You can buy the belts from Stillen directly, but their price was $54.00. I recommend getting the belts locally. Follow the factory procedure to put the new belts back on, and tighten them to factory specs. Now you can torque the crank pulley bolt to 140 ft-lbs. Again - follow the same procedures you used earlier to secure the flywheel from rotating. Torquing this bolt properly is very important - USE A GOOD TORQUE WRENCH. The last thing you need is to have your crank pulley come flying off the engine during spirited driving. I also cannot stress enough the importance of belt tension. FOLLOW THE FACTORY MANUAL. For a new compressor belt the deflection should be 3.8-4.1 mm, and the power steering belt should be 6.5-7 mm. If you do not tension these belts properly they will squeak like a stuck pig!!
	That's it. Put the oil cover and flywheel rear cover plate back on, put the passenger wheel back on, torque the lug nuts to 85 ft-lbs and drive away!. I noticed an immediate improvement in low-end torque, which increased over time as the ECU in the Maxima got used to the new pulley. I would estimate that about 75% of the improvement comes right away, with the other 25% coming as the ECU re-adjusts.