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Belt Tensioner Stop
 
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Pelican Technical Article:

Belt Tensioner Stop

Time:

30 mins

Tab:

$20

Talent:

*

Tools:

13mm wrench

Applicable Models:

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

Parts Required:

tensioner stop

Hot Tip:

Check the condition of the drive belt and the belt tensioner

Performance Gain:

cheap insurance against a costly failure

Complementary Modification:

Replace serpentine belt
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.

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. 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.

It's a pretty good setup except for a small design flaw. If the serpentine belt snaps while the engine is running, the energy released can drive the tensioner pulley and strut right into the crank pulley. There is a failsafe built into the system: a small 'T' shaped twist at the end of the tensioner spring. The idea is that the small 'T' acts as stop, preventing further travel.

The problem with this design is that the force of the belt snapping can sometimes break the small 'T' off the end of the spring. (See Figure 1) If the 'T' snaps off, it can throw the tensioner into the crank pulley. Since the crank pulley is constantly turning while the engine is running, this can cause a great deal of damage. I've heard of people having to replace the entire tensioner assembly, the crank pulley and also damage to the other pulleys. This can add up to over $1000 to repair.

The solution is to install a tensioner stop. This is a piece of stainless steel that physically wraps around the dampener and limits the travel of the tensioner arm. There are a few different companies that produce these stops. In our case, we used the one manufactured by Alta Performance (See Figure 2). Alta has designed the stop to limit the travel of the tensioner to the same point as the OEM tensioner stop. This allows for normal travel of the tensioner up to the point at which the OEM tensioner stop fails. At $20 and only taking 30 minutes to install, it's cheap insurance against a potential problem. In this article I will go over the steps involved with installing the tensioner stop.

Begin by jacking up the front of the car, placing it on jack stands and removing both the passenger side front tire and the inner wheelhouse liner. See our articles on Jacking Up Your Car and Front Bumper Removal for more info. Once the wheelhouse liner is removed, you'll see the tensioner dampener right above and to the left of the crank pulley (See Figure 3).

Find the 13mm bolt securing the dampening strut near the front of the motor (See Figure 4). You will want to loosen this bolt just enough to slip the smaller end of the tensioner stop under the head of the bolt (See Figure 5). Don't remove the bolt completely, you just need to get it over the bolt. Now, place the rubber sleeve that came with the stop inside and over the top rib of the stop. This prevents excessive rattling when the stop is installed (See Figure 6). Now rotate the other end of the stop up and over the other end of the dampening strut. You'll want to press the end of the stop as far down the other side as you can. This prevents the end from slipping off the strut if the belt lets go (See Figure 7). Take note that you may need to compress the tensioner slightly in order to fit the end of the stop over the dampening strut. Now tighten the front 13mm bolt back up and you're done. Reinstall the wheelhouse liner, put the tire back on and lower the car down.

Shown here is a failed factory stop (green arrow) compared to a new one (yellow arrow).
Figure 1

Shown here is a 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.

A tensioner stop is cheap insurance against a potentially expensive repair.
Figure 2

A tensioner stop is cheap insurance against a potentially expensive repair. There are several different stops on the market, however they all work in the same way, preventing the tensioner from over travel if the failsafe inside the tensioner fails.

With the tire and wheelhouse liner removed, you'll see the dampening strut for the tensioner right in front of you.
Figure 3

With the tire and wheelhouse liner removed, you'll see the dampening strut for the tensioner right in front of you.

Shown here are the two bolts that secure the dampening strut to the tensioner assembly.
Figure 4

Shown here are the two bolts (green and purple arrows) that secure the dampening strut to the tensioner assembly. Loosen (but do not remove) the front bolt (green arrow).

Place the supplied rubber sleeve inside and over the top rib of the stop.
Figure 5

Place the supplied rubber sleeve inside and over the top rib of the stop. This prevents the stop from rubbing on the dampening strut which can cause some rattling. Now slide the smaller, angled end of the tensioner stop over the loose bolt. You want the bolt to ride in the groove in the stop. It's somewhat difficult to get a picture showing how do this inside the car. I've taken this picture with the tensioner removed to make it more clear.

Now push the stop over the other end of the dampening strut, taking care to push the end of the stop back over the collared end.
Figure 6

Now push the stop over the other end of the dampening strut, taking care to push the end of the stop back over the collared end. This picture shows the approximate position you want the stop to be oriented over the end of the strut. You don't want the end to be centered over the head of the bolt, as it can slip off.

ThisPicture shows the tensioner stop installed inside the car over the tensioner damper.
Figure 7

This picture shows the tensioner stop installed inside the car over the tensioner damper. Once in place, make sure that the small groove is pushed back as far as it will go (the yellow arrow indicates the direction) and tighten the 13mm nut, locking it in place (green arrow).

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Comments and Suggestions:
autodoc Comments: why would the tensioner go anywhere? Even if both the damper and the stop failed, wouldn't the belt have to be broken or fallen off for the stop to even be reached?
May 13, 2016
  Followup from the Pelican Staff: I think if the strut fails, this piece prevents the tensioner from hitting the crank pulley, causing more damage. - Nick at Pelican Parts  
808mini Comments: Is it possible to take the whole tensioner off without lifting the engine? Is it possible to take off the dampening strut without taking off the tensioner?
November 29, 2013
  Followup from the Pelican Staff: No, the engine mount has to be removed. SO you have to jack it up a bit. - Nick at Pelican Parts  

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