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Pelican Technical Article:
Belt Tensioner Replacement

Jared Fenton
 

 
Time: 2 hours
Tab: $160
Talent:  
Tools:
Socket set, Serpentine belt tool
Applicable Models:
R50 MINI Cooper (2002-06)
R53 MINI Cooper S (2002-06)
R52 MINI Cooper Convertible (2005-08)
R52 MINI Cooper S Convertible (2005-08)
R55/R56/R57 Cooper/Cooper S (2007-12)
Parts Required:
belt tensioner
Hot Tip:
Use the tools to retract the belt tensioner
Performance Gain:
peace of mind against a costly failure
Complementary Modification:
Install an underdrive pulley on the supercharger
 
   

  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 2012. See The Official Book Website for more details.
 

Check out some other sample projects from the book: 

Need to buy parts for this project? Click here to order!
   
     The MINI Cooper S uses a serpentine belt to drive the various ancillary components on the engine. This includes the alternator, A/C compressor and the supercharger/water pump. The serpentine belt is kept in place by a small dampener and a coil spring mounted to the end of an idler pulley. This is called a belt tensioner. Over time, the serpentine belt can stretch. The tensioner setup is designed to allow a certain amount of flex to account for stretching as well as vibration.

     The first step is to disconnect the battery as you will be working around the engine. It’s cheap insurance against accidentally touching an 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 (See Figure 2). Squeeze the tabs on both the top and bottom to remove the connections (See Figure 3 and Figure 4 ). Underneath the valve you will also see an electrical plug that must be disconnected (See Figure 5). 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 (See Figure 6).

     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 (See Figure 7). 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 (See Figure 8).

     Next, jack up the front of the car and secure it on jack stands and remove the front splash shield under the front of the car.

     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 as shown in Figure 9. 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 (See Figure 10).

     Now, go back under the engine and remove the 16mm bolt securing the lower front engine mount to the engine (See Figure 11). Next, 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 (See Figure 12).

     Now remove the upper passenger mount assembly. Start by removing the nut and bolt that secures the ground cable (See Figure 13). Next remove the 8mm bolt securing the hose bracket to the mount brace (See Figure 14). Now remove the two 16mm bolts that secure the front mount to the mount located on the passenger side wheelhouse (See Figure 15 and Figure 16 ). Remove the 16mm nut securing the mount to the engine bracket (See Figure 17). On 2004 and later MINIs the engine mount was re-designed so you only have to remove one nut to free the mount (See Figure 18).

     At this point, start carefully jacking up the engine. The idea here is to make the belt tensioner accessible from the passenger side of the engine. Once the supercharger pulley is visible as shown in Figure 20, stop jacking. Keep an eye out for any cables or items that may be binding or getting caught. If you encounter this, stop, carefully rectify the problem and move on.

     You’ll need to remove the passenger side engine mount from the frame rail in order to access the tensioner bolts. Feel underneath the rail. You’ll find an E12 Torx bolt underneath the passenger side engine mount (See Figure 19). This long bolt secures the mount to the frame rail. Once removed, take the engine mount off the frame rail. Now remove the long 16mm bolt securing the tensioner arm to the engine (See Figure 20). Then remove the two 10mm bolts near the front of the tensioner and the 16mm bolt at the rear (See Figure 20). Once these bolts are removed, the tensioner can be maneuvered out from the side of the engine (See Figure 21 and Figure 22 ).

     Compare the new tensioner to the old one. In our case, the tensioner stop in our project car had sheared off of the somewhat flimsy sheet metal (See Figure 23). This small piece of metal is designed to hold the massive tension of the spring if the dampener strut fails. It's a good idea to also install a tensioner stop as added insurance. See our article on installing a belt tensioner stop for more info.

     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 (As shown in Figure 17 and Figure 18 ) and torque it to 68Nm (50ft/lbs.).

     You can now lower the jack. Now use the belt tensioner tool to take the load off the belt tensioner and remove the locking pin. Make sure that the belt is correctly seated on all the pulleys. All that remains at this point is to refit the air box, the fuel tank vent valve and the radiator hose bracket.

     The Non-S Cooper models use a different design for the belt tensioner, however, it does require that you remove the engine mount as with the Cooper S. Begin by removing the serpentine belt (Refer to our article on serpentine belt replacement for more information). Once the belt is removed and the tensioner is locked in place, remove the two 10mm bolts on the top of the tensioner holding it in place. Next remove the remaining 10mm bolt at the bottom of the tensioner. This bolt has to be accessed from inside the wheel well. Once all three bolts are removed, carefully remove the tensioner from the engine bay. The new one just bolts up into place.

     The R55/R56/R57 models are a bit different then the early cars. These cars use a lever type belt tensioner with a lock mechanism built in. To replace the belt tensioner, first remove the headlights, serpentine belt and lock carrier.

     Once the serpentine belt is removed from the engine, loosen and remove the two Torx bolts on the front of the tensioner and lift it away from the engine. Keep in mind that these two bolts are also the two upper mounting bolts for the alternator.
Shown here is a new serpentine belt tensioner assembly.
Figure 1
Shown here is a new serpentine belt tensioner assembly. Over time, the tensioner can fail, possibly causing damage to the crankshaft pulley if the tensioner stop fails. Shown here is a new unit, available from Pelican Parts.
Large Image | Extra-Large Image
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)
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
In thisPicture, you can see the belt tensioner in it's locked position.
Figure 8
In this picture, you can see the belt tensioner in it's 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.
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
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).
Large Image | Extra-Large Image
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).
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
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.
Large Image | Extra-Large Image
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).
Large Image | Extra-Large Image
Remove the E12 Torx bolt underneath the passenger side engine mount.
Figure 19
Remove the E12 Torx bolt underneath the passenger side engine mount. This long bolt secures the mount to the frame rail. Once removed, take the engine mount off the frame rail. You will need the extra space to remove the belt tensioner.
Large Image | Extra-Large Image
Now remove the long 16mm bolt securing the tensioner arm to the engine at the front as shown here.
Figure 20
Now remove the long 16mm bolt securing the tensioner arm to the engine at the front as shown here. 
Large Image | Extra-Large Image
Then remove the two 10mm bolts near the front of the tensioner and the 16mm bolt at the rear (green arrows).
Figure 21
Then remove the two 10mm bolts near the front of the tensioner and the 16mm bolt at the rear (green arrows). Once these bolts are removed, the tensioner can be maneuvered out from the side of the engine.
Large Image | Extra-Large Image
Here's a view of the engine with the belt tensioner removed.
Figure 22
Here's a view of the engine with the belt tensioner removed.
Large Image | Extra-Large Image
Shown here is the failed factory stop (green arrow) compared to a new one (yellow arrow).
Figure 23
Shown here is the failed factory stop (green arrow) compared to a new one (yellow arrow). As you can see, the tensioner stop in our project car had sheared off of the somewhat flimsy sheet metal. This small piece of metal is designed to hold the massive tension of the spring if the dampener strut fails. It's a good idea to also install a tensioner stop as added insurance. See our article on installing a belt tensioner stop for more info.
Large Image | Extra-Large Image
Here is the new belt tensioner installed on the side of the engine.
Figure 24
Here is the new belt tensioner installed on the side of the engine. At this point re-install the passenger side engine mount and lower the engine back onto the mount. Re-fit the serpentine belt, and use the belt tool to relieve tension on the belt.
Large Image | Extra-Large Image
(R50 Cooper) On the Cooper models, the belt tensioner is a different design; however you will need to follow all of the steps in removing the passenger side engine mount in order to access the tensioner.
Figure 25
(R50 Cooper) On the Cooper models, the belt tensioner is a different design; however you will need to follow all of the steps in removing the passenger side engine mount in order to access the tensioner. Remove the two 10mm bolts at the top as shown here (green arrows).
Large Image | Extra-Large Image
(R50 Cooper) Remove the 10mm bolt at the bottom of the belt tensioner (green arrow).
Figure 26
(R50 Cooper) Remove the 10mm bolt at the bottom of the belt tensioner (green arrow). You will need to remove this bolt from the bottom of the frame rail. Once removed, you can remove the old tensioner from the engine.
Large Image | Extra-Large Image
(R50 Cooper) Shown here is the new belt tensioner for the Non-S Cooper models.
Figure 27
(R50 Cooper) Shown here is the new belt tensioner for the Non-S Cooper models. It will come with the locking pin installed. Do not remove the locking pin until the tensioner is installed.
Large Image | Extra-Large Image
(MK2 Cooper and Cooper S) On the R55/R56/R57 MINIs, the belt tensioner is more easily removed.
Figure 28
(MK2 Cooper and Cooper S) On the R55/R56/R57 MINIs, the belt tensioner is more easily removed. Once you have removed the lock carrier, headlights and serpentine belt, locate the two Torx bolts shown here (green arrows) to remove the belt tensioner from the engine.
Large Image | Extra-Large Image
Need to buy parts for this project? Click here to order!
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Comments and Suggestions:
JoshRan Comments: You note that on the R50, the engine mount also needs to be removed. Just did mine, and that is not required. Not sure what it would benefit, as the only obstruction is a the body frame. Also, it is much easier to put the new pulley on in a 'relaxed' mode no pin, then retract once it is bolted in place.
October 4, 2014
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
JeanPaul Comments: How to do this without jacking the engine. After removing the belt and inserting the locking pin in place, unbolt the dampener hydraulic shock from the tensioner before unbolting the tensioner from the engine. Now If you move the unbolted tensioner toward the front and rotate it clockwise it should almost fall out. Reinstallation is even easier, just remember to bolt the damper back on before motoring. I was able to accomplish this swap in 35 minutes start to finish at a relaxed pace.
September 6, 2014
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
 
George. Comments: After following your detail on replacing the belt idler arm on my R50 Mini Cooper I found the following method, as shown in the photograph, worked great in order to pull back against the tensioner spring.
July 1, 2014
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
George. Comments: After following your detail on replacing the belt idler arm on my R50 Mini Cooper found I the following method, as shown in the photograph, worked great in order to pull back against the tensioner spring.
July 1, 2014
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
Mini Shirk Comments: I'm going to 2nd CooperSml here. These post have been most helpful!! Do you have a picture of the lock carrier?
May 13, 2014
  Followup from the Pelican Staff: No, I don't have a photo to share.

Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
nunoluis Comments: Hey there. Any plans on releasing a service manual for the MINI? In your page "The Official Book Website" there is no link for a MINI book... Also, how much will it cover pics, detailed HOW TOs, etc the R56, 2nd Gen? Thanks for all the info at Pelican Parts!
March 5, 2014
  Followup from the Pelican Staff: There may be some things in the works. I know there is a Bentley Publishers R56 manual. We can send one you to.
Give our parts specialists a call at 1-888-280-77 - Nick at Pelican Parts
 
Alan Comments: I recently replaced the bearing on my cooper s tensioner pulley assy
I found that I only had to remove the top engine mount assy and then the
Belt tensioner was abled to be jiggled out, also I just used a 600 mm
Approx piece of 25/25angle iron with a small cut out on one side and it
Worked fine for detensioning the spring,TIP be absolutely sure to put belt on correctly,
April 28, 2013
  Followup from the Pelican Staff: Thanks for the feedback and tip. - Nick at Pelican Parts  
cooperSml Comments: Detail of the tensioner belt removal tool on the belt tensioner
April 17, 2013
  Followup from the Pelican Staff: Thanks for the image. Looks great! - Nick at Pelican Parts  
cooperSml Comments: The strut on the belt tensioner had a broken ring and it was making a metal sound when the car was on idle or going to a stop because it was almost loose. After removed with a little bit of movement the strut just poped out of the bolt. I was very lucky.
April 17, 2013
  Followup from the Pelican Staff: Glad you caught it. Thanks for the feedback. - Nick at Pelican Parts  
cooperSml Comments: I would like to say thank to Pelican for the service, parts and this type of technical information. They are so helpful anytime you need a piece of information in how to do it right. Regarding the belt tensioner I was able to replace it without lift the engine.
April 17, 2013
  Followup from the Pelican Staff: Thanks for the feedback. - Nick at Pelican Parts  

Check out some other sample projects from the book: 

 

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  Applies to: R50 MINI Cooper (2002-06) - R53 MINI Cooper S (2002-06) - R52 MINI Cooper Convertible (2005-08) - R52 MINI Cooper S Convertible (2005-08) - R52 MINI Cooper S Convertible (2005-08) - R56 MINI Cooper (2007-) - R57 MINI Cooper Convertible (2007-)
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