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Underdrive Pulley Install
 
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Pelican Technical Article:

Underdrive Pulley Install

Time:

2 hours2 hrs

Tab:

$65

Talent:

***

Tools:

Socket set, Pulley removal tool, Serpentine belt tool

Applicable Models:

R52 MINI Cooper S Convertible (2005-08)
R53 MINI Cooper S Hatchback (2002-06)

Parts Required:

underdrive pulley, John Cooper Works serpentine belt.

Hot Tip:

Use a smaller belt to account for the reduced size of the pulley

Performance Gain:

increased boost pressure equals more power

Complementary Modification:

Install performance software, install cooler running spark plugs
How to Maintain and Modify your new MINI

This article is one in a series that have been released in conjunction with Pelican Parts' new book, How to Maintain and Modify your new MINI The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 500+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any MINI owner's collection. The book is due to be released in late 2015. See The Official Book Website for more details.

If you have a MINI Cooper S, one of the most cost effective modifications you can perform is to install an underdrive pulley on the supercharger. The MINI Madness 15% reduction pulley will add about 3 or 4 pounds of boost which translates into about 15-20 horsepower over stock. With an aftermarket intake and/or exhaust, it can make even more power.

The first step is to disconnect the battery as you will be working around the engine. It's cheap insurance against accidentally touching a electrical connector or terminal and causing damage to the vehicle's electrical system.

Move over to the passenger side of the engine and remove the fuel tank vent valve. It is located right above the tensioner. Squeeze the tabs on both the top and bottom to remove the connections. Underneath the valve you will also see an electrical plug that must be disconnected. Pull the tab on the side of the plug and pull it off. Lastly, push the tab to the side of the valve and remove it from the engine.

Now, place the serpentine belt tool over the belt tensioner and pull toward you. This will release the tension on the belt from the tensioner. Once the second hole protrudes from the tensioner, stick the retaining pin through it to lock the tensioner in place and remove the serpentine belt.

Next, jack up the front of the car (Refer to our article on jacking up the MINI for more info) and remove the front splash shield under the front of the car. (Refer to our article on bumper removal for more info)

Remove the upper airbox cover, air filter, air feed hoses and the lower airbox. (Refer to our article on installing a cold air intake for more info) You will need to remove these items to access one of the bolts on the transmission mount. Next place a floor jack with a block of wood under the center of the engine. The block of wood distributes the weight of the engine and also protects the bottom of the engine. Take up the weight of the engine with the floor jack. Now, loosen the long 16mm bolt that secures the rubber transmission mount to the Bracket on the driver's side of the engine compartment.

Now, go back under the engine and remove the 16mm bolt securing the lower front engine mount to the engine. Now, look at the front of the engine where the radiator hose runs just under the intercooler and remove the clamp holding the radiator hose in place.

Now remove the upper passenger mount assembly. Start by removing the nut and bolt that secures the ground cable. Next remove the 8mm bolt securing the hose bracket to the mount brace. Now remove the two 16mm bolts that secure the front mount to the mount located on the passenger side wheelhouse. Now, remove the 16mm nut securing the mount to the engine bracket. On 2004 and later MINIs the engine mount was re-designed so you only have to remove one nut to free the mount.

At this point, start carefully jacking up the engine. The idea here is to make the supercharger pulley accessible from the passenger side of the engine. Once the supercharger pulley is easily accessible, stop jacking. Keep an eye out for any cables or items that may be binding or get caught. If you encounter this, stop, carefully rectify the problem and move on.

With the supercharger pulley now in view, start by removing the 16mm bolt securing the tensioner arm to the engine. This will give you a bit more clearance to fit the pulley removal tool over the pulley. Now unscrew the small plastic plug in the center of the pulley.

The stock supercharge pulley on the MINI Cooper S is a press fit onto the shaft. This can present some problems in removing it. The factory manual specifies remove the entire engine mount and also a specialized puller from BMW. The guys over at MINI Madness have come up with a much simpler tool to make the job much, much easier. Their EZ Pulley removal tool really makes pulling off the pulley a easier job. NEVER try to beat the pulley off the shaft. You could risk damaging the bearings in the supercharger. Use the right tool for the job.

The pulley tool has a series of grooves on the inside edge that grasps the stock pulley and allows it to be pulled off as you tighten the bolt. One side of the tool is also open to allow you to maneuver it into place around the pulley. Start out by removing the bolt in the tool and fitting the grooved portion over the stock pulley. You will likely need to move the tensioner arm a bit to get the tool right in place. Thread the bolt all the way down until you can't turn it by hand anymore.

Next, thread the specialized bolt into the center of the tool and inside the center of the pulley. Make sure that the bolt centers in the hole before you start tightening it. The next step is to counterhold the grooved portion of the tool while you tighten the bolt. Take a large crescent wrench and hold the grooved part of the tool while you tighten the bolt. As it tightens, the pulley will start to come off the shaft. Keep tightening the bolt until you can take the pulley off.

It's a good idea to clean off any dirt or grease around the shaft at this time. It's important to have a clean mating surface when you put the new pulley on. The 15% reduction pulley is a two-piece design. You have the inner portion of the pulley called a collet and the outer, grooved section that the belt rides on. The nice thing about this design is that as you tighten the bolts, the collet locks the outer pulley onto the shaft and keeps it in place.

Place the collet end of the pulley onto the shaft and push it back as far as it will go. (See Figure 26) Now take the supplied mm bolts and place them through the outer pulley half and apply a small amount of Loctite to the threads. This will prevent the bolts from backing out once turned. Place the outer pulley half over the collet on the shaft, making sure that the collet is pushed back all the way and thread the hex bolts into the collet. Tighten the pulley bolts by hand using a cross-tightening method. Torque the bolts to around 60 in-ft/lbs. or 3Nm. After they are tight, go over the cross-tightening procedure again to double check.

It's recommended that you use the supercharger belt from the John Cooper Works package. This belt is slightly smaller than the stock belt and makes up for the reduced size of the pulley. This belt is available through PelicanParts.com, Part number 11-28-7-545-120. Install the shorter serpentine belt over the new pulley and re-install the belt tensioner bolt removed before. Make sure that the belt is correctly routed over all the pulleys.

Now, carefully lower the engine back down over the passenger side motor mount bolt. Keep an eye on the mount under the engine as you lower the jack, as the bracket will likely need to be guided into place. Place the 16mm bolt through the lower engine connection, but don't tighten it just yet.

Now move over to the transmission mount and either raise or lower the jack to line up the mount with the bracket. Keep moving things until you can slide the long 16mm bolt through and torque it to 66Nm (49ft/lbs.) Now tighten the lower engine connection bolt to 38Nm (28ft/lbs.) Refit the 16mm nut on the bracket and torque it to 68Nm (50ft/lbs.) Now refit the engine mount brace for pre 2004 cars and torque each bolt.

You can now lower the jack. All that remains at this point is to refit the air box, the fuel tank vent valve and the radiator hose bracket. You can now enjoy the substantial increase in power.

Shown here is the 15% supercharger reduction pulley from MINI Madness.
Figure 1

Shown here is the 15% supercharger reduction pulley from MINI Madness. This is probably the most cost effective means of increasing horsepower in your MINI Cooper S. Installation of this pulley usually results in a 3-4 pound boost in supercharger pressure, which translates roughly to 15-20 horsepower over stock. Further modifications to your engine's flow rate (such as exhaust or head work) will result in even more power generated.

Begin by removing the fuel tank vent valve directly above the belt tensioner and supercharger pulley.
Figure 2

Begin by removing the fuel tank vent valve directly above the belt tensioner and supercharger pulley. In this picture, you can see the upper vent valve connection (purple arrow) the electrical harness connector (green arrow) and the lower vent valve connection (yellow arrow).

Remove the lower vent valve connection by squeezing the two tabs on the out side of the connector and pulling it off.
Figure 3

Remove the lower vent valve connection by squeezing the two tabs on the out side of the connector and pulling it off. Take care not to use too much force on the plastic line.

Next, remove the upper vent valve connection by pressing the tabs on the connector and pulling it up.
Figure 4

Next, remove the upper vent valve connection by pressing the tabs on the connector and pulling it up. Again, take care not to damage the plastic line.

Use a small screwdriver to pull back on the plastic tab securing the electrical harness plug to the valve and pull it down and off the valve.
Figure 5

Use a small screwdriver to pull back on the plastic tab securing the electrical harness plug to the valve and pull it down and off the valve.

Press the small tab on the mounting bracket (green arrow) and slide the vent valve off.
Figure 6

Press the small tab on the mounting bracket (green arrow) and slide the vent valve off. Set it aside for the time being.

ThisPicture shows the belt tensioner tool mounted over the tensioner and ready to be pulled back to install the safety pin.
Figure 7

This picture shows the belt tensioner tool mounted over the tensioner and ready to be pulled back to install the safety pin.

In thisPicture, you can see the belt tensioner in its locked position.
Figure 8

In this picture, you can see the belt tensioner in its locked position. (Keep in mind that the upper left engine mount has been removed for clarity in this picture.) As you pull back on the belt tensioner tool, the tensioner retracts and the tensioner arm emerges from the spring assembly. Place the safety pin (green arrow) through the second hole on the tensioner arm (yellow arrow) The tension will now be relieved from the belt.

Place the floor jack under the center of the engine with a block of wood to distribute the weight of the engine and also to protect the oil pan.
Figure 9

Place the floor jack under the center of the engine with a block of wood to distribute the weight of the engine and also to protect the oil pan.

With the airbox and hoses removed, you now have access to the transmission mount.
Figure 10

With the airbox and hoses removed, you now have access to the transmission mount. With the floor jack under the engine and secure, remove the long 16mm bolt securing the mount to the bracket (green arrow).

Remove the 16mm bolt securing the lower passenger side mount to the engine (green arrow).
Figure 11

Remove the 16mm bolt securing the lower passenger side mount to the engine (green arrow).

Remove the 8mm bolt that secures the upper radiator hose to the front off the intercooler.
Figure 12

Remove the 8mm bolt that secures the upper radiator hose to the front off the intercooler. This will allow some flex in the upper radiator hose when you jack the engine up.

Remove the ground strap from the engine mount bracket on the passenger side of the car.
Figure 13

Remove the ground strap from the engine mount bracket on the passenger side of the car. Be sure not to lose the bolt which fits up underneath the bracket as it can fall out once you remove the ground nut.

Remove the small 8mm bolt securing the bracket holding the two hoses to the engine mount brace.
Figure 14

Remove the small 8mm bolt securing the bracket holding the two hoses to the engine mount brace. Move the bracket out of the way for the time being, or pop the hoses out of it and set the bracket aside.

Remove the 16mm bolt at the front of the engine mount brace.
Figure 15

Remove the 16mm bolt at the front of the engine mount brace.

Next, remove the 16mm bolt securing the engine mount brace at the rear.
Figure 16

Next, remove the 16mm bolt securing the engine mount brace at the rear. Keep in mind that the engine may move back a little. Make sure that the jack with the block of wood is fully supporting the weight of the engine.

Now remove the 16mm nut holding the engine mount bracket to the engine mount (green arrow) Once removed, carefully jack the engine up and off the engine mount.
Figure 17

Now remove the 16mm nut holding the engine mount bracket to the engine mount (green arrow) Once removed, carefully jack the engine up and off the engine mount.

On 2004 and later MINIs, the passenger side engine mount was redesigned.
Figure 18

On 2004 and later MINIs, the passenger side engine mount was redesigned. If you own one of these cars, you simply remove the ground strap (yellow arrow) and the 16mm nut on the top of the bracket (green arrow).

Remove the 16mm bolt on the tensioner arm.
Figure 19

Remove the 16mm bolt on the tensioner arm. Removing this bolt will allow some movement of the tensioner arm which helps in both removing and replacing the serpentine belt as well as fitting the pulley removal tool over the pulley.

Unscrew the small black plastic tab in the center of the stock pulley.
Figure 20

Unscrew the small black plastic tab in the center of the stock pulley.

The EZ Pulley Removal tool from MINI Madness turns a much harder job into a relatively easy one.
Figure 21

The EZ Pulley Removal tool from MINI Madness turns a much harder job into a relatively easy one. Rather than the large multi-piece factory tool, this unit slips right over the pulley and pulls it off the shaft with two wrenches.

Unscrew the bolt from the tool and place the grooved section of the tool over the stock pulley.
Figure 22

Unscrew the bolt from the tool and place the grooved section of the tool over the stock pulley. You may need to move the belt tensioner arm to get a bit more access.

Thread the bolt potion of the MINI Madness tool through the grooved portion and into the stock pulley until it seats.
Figure 23

Thread the bolt potion of the MINI Madness tool through the grooved portion and into the stock pulley until it seats. Make sure that you have centered both the tool and the bolt in the center of the pulley.

Use a large crescent wrench to hold the grooved section of the tool while you tighten the bolt.
Figure 24

Use a large crescent wrench to hold the grooved section of the tool while you tighten the bolt. As the bolt tightens, it will pull the stock pulley off the supercharger shaft.

It's a good idea to clean the pulley shaft thoroughly to remove all dirt and grease from the area.
Figure 25

It's a good idea to clean the pulley shaft thoroughly to remove all dirt and grease from the area.

Place the inner, collet half of the reduction pulley on the supercharger shaft and push it all the way back until it stops.
Figure 26

Place the inner, collet half of the reduction pulley on the supercharger shaft and push it all the way back until it stops. The unique design of the collet will lock the pulley in place when you install the outer half.

Place the supplied hex bolts through the outer pulley half and put a dab of Loctite on each bolt.
Figure 27

Place the supplied hex bolts through the outer pulley half and put a dab of Loctite on each bolt. This will prevent them from backing out. Place the outer pulley half over the collet and push it all the way back while threading in the bolts.

Slip the belt back over the pulley and cross-tighten the bolts to approx.
Figure 28

Slip the belt back over the pulley and cross-tighten the bolts to approx. 3Nm (60in/lbs.) by hand. Make sure to double check that all bolts have been tightened and that the pulley is firmly seated as far as it will go back on the shaft. Once done, re-install the 16mm bolt securing the tensioner to the engine as seen in the photo.

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Comments and Suggestions:
David06r53mini Comments: Hi. Yup. Had to have a shop load codes into ECU. Runs great now. Now I know the power supply must be backed up prior to disconnecting battery leads...
January 21, 2016
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
 
David06r53mini Comments: Hi. Did the 15 % pulley, NEW BELT and plugs. Sadly, disconnected battery and now car runs horrible... Did ECU loose tuning orders with batt disconnect? What should I do now? Visit Dealer $$$? DIY Tuning software? Please help! THANKS! GREAT SITE!
January 17, 2016
  Followup from the Pelican Staff: May be a software issue. I would start by reloading your performance software. - Nick at Pelican Parts  
JonHuerta Comments: Hi Friends i have a query more % in pulley means more HP?
October 7, 2014
  Followup from the Pelican Staff: Changing the pulley can increase boost. - Nick at Pelican Parts  
ROS Comments: CAN YOU INSTALL A CENTER BOLT FOR ADDED SUPPORT, WHEN INSTALLING A SMALLER PULLY.
June 18, 2014
  Followup from the Pelican Staff: I have not done that and do not think it will help. The pulley is pressed on. - Nick at Pelican Parts  
Jack Comments: I just had this done by a local shop. I think they may have broke the hydraulic motor mount on the passenger side on my 2004 S. The nut was freshly rounded and the motor mount started leaking a lot after a hour or 2 of driving. Shop said they didn't touch the motor mount and to install the pulley they removed the front bumper. I havent seen anything on the internet that says it can be done without raising the engine. Could they have done it without raising the engine? Am I getting a runaround? thanks - btw before the mount went it was pretty sweet upgrade
June 2, 2014
  Followup from the Pelican Staff: I have not done it without jacking the engine. This is because the pulley is lower than the engine compartment. I would think they would have had to jack it also. - Nick at Pelican Parts  
R53 Comments: So I only have basic car knowledge. Is this a job that I could do myself safely? It seems pretty straight forward, but I wouldn't want to make my car unsafe on the road. Also, do you have or know of any videos for this job? Great written instructions!
March 29, 2014
  Followup from the Pelican Staff: This is a bit of an advanced procedure. I would not perform it if you are unsure of your ability. - Nick at Pelican Parts  
BigErn Comments: Does the supercharger pulley has a bolt in the center that holds it in place? I don't see you mentioning a center bolt after removing the small black plastic tab in the center of the stock pulley.
August 21, 2013
  Followup from the Pelican Staff: There is no center bolt on the factory MINI puller. It is pressed on. - Nick at Pelican Parts  
Bryan Comments: Just curious what you think about an overdrive crank pulley 2% with the 15% under drive SC Pulley? Will this damage the alternator or electrical system? Also, I don't see any procedure for replacing the timing chain, guide rail, tension rail and tensioner. Is this something good to do since I have my Mini S in pieces right now? 2002 Mini S R53. Thanks. Can't wait to get your book for my Boxster!
August 13, 2013
  Followup from the Pelican Staff: I personally wouldn't mix two under-drive pulleys. I'd pick one and stick with it.

If you have the engine apart, it's not a bad idea to replace the timing chain componenets. However we do not currently have a tech article for that procedure. You could grab a repair manual, it would be in it. Give our parts specialists a call, they will help you find the right manual and parts.- Nick at Pelican Parts
 
E-tek Comments: Thanks for the great step by step - as usual! I have your Boxster book and it's great too. For this project I made my own tensioner tool but may have given up on the project without seeing this page. You guys are awesome!
August 11, 2012
  Followup from the Pelican Staff: Thanks for the feedbacjk. We're glad to help. Can you share a photo of your tool? - Nick at Pelican Parts  

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