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 (Note:
this article was writen when we did our very first pulley,
much has changed and we are aware that these techniques
may be out of fashion)
What
makes the Mini Cooper S more fun than the regular Cooper?
Power! And where does the power come from? The supercharger!
And what would make the Cooper S even more fun? Even more
power! Add another supercharger! Well, no, we can't do that.
But we can make the supercharger spin faster by changing
the drive pulley to a smaller one. Supercharger spins faster,
makes more pressure, makes more fun.
A bit of web searching told
us that we were going to have to have some sort of tool
to remove the existing pulley: either the Minimania destructo
tool or the BMP Promini gear pulling tool. We opted for
the less destructive route and got our gear and tool from
BMP. Both the gear and the tool are beautiful pieces.
And on to the installation,
BMP says it should only take 3 hours, so I should be done
by lunch...
Installation
Step 1. Choose a nice Saturday, relatively free from interruptions.
9.00AM: Read the directions---whoops, there are no directions.
Look on the BMP Promini website---no directions there either.
Fortunately, Minimania DOES publish technical material and
their website had some important clues.
9.15AM: Locate the supercharger
on the engine. Oh, man---that thing is buried! Remove the
 right
front wheel if you're strong enough---it's heavy! The run-flat
tire and wheel weigh 49 pounds [including about a pound
of brake dust]. Next remove the RF plastic inner fender
liner, breaking about half of the plastic attachment screws
in the process. Chopping with a screwdriver and replacing
them with new (Part number 07 13 0 702 966) is the fastest
way to get past them once they stripped.
Removing of the right upper
motor mount bolts and bracket come next, followed by the
motor mount bolt at the bottom right, next to the power
steering cooling fan. Support the engine with a floor jack.
No, on second thought, put that bolt back in loosely and
jack up the engine with that floor jack. Jack it up so that
it pivots backwards as it raises and get it high enough
that the compressor pulley almost clears the frame.
10.20AM: Compress the belt
tensioner shock with a large screwdriver and place a tiny
screwdriver in the hole at the spring to hold the tension
there so that the belt itself is released. Remove the belt
tensioner assembly----but first make a drawing of the belt
routing!!! Don't forget to do this---it'll be much harder
later.
11.20AM: Finally! Down to
the supercharger gear. Install the Promini  removal
tool---it fits perfectly. Tried various pullers---two and
three jawed pullers were too big, but a steering wheel puller
fit well enough to allow the gear to come most of the way
off, and light tapping got it the rest of the way.
12.00 Noon: Three hours are
gone so I must be done. Oops---I still have to put it all
back together. Start by tapping the new gear hub into place
until it's about 1/8 inch from the aluminum supercharger
housing [as directed by the Minimania website]. Attach the
outer pulley to the hub using the supplied 4mm Allen bolts.
How tight should they be? Good question---the Minimania
pulley uses larger bolts tightened to 70 inch pounds, so
these should be tightened less than that. I tightened these
as much as I dared, and used red Loctite on the bolt threads
to ensure that they won't vibrate out. The pulley
was kept from turning by wrapping the old belt around it
and grabbing tightly against the pulley with a vicegrips.
Worked great.
12.30PM: Drop the engine
back into place, remove the old belt, and have lunch.
2.00PM: Reinstall belt tensioner
assembly and take a half hour or so to put on the new belt.
That thing fits tight. Remember to let the tensioner loose
by pulling out the pin that releases the spring.
2.45PM: start the engine
to see if everything lines up. Yeah, it works! Put back
the fender  liner,
the wheel, and the motor mount bolts.
3.30PM: Test drive---WOW!
I had been wondering why the factory didn't make these cars
with a smaller pulley and now I know. The tires spin all
the time---up hills, on acceleration from stops, over the
top of hills when the car gets light---all those everyday
driving circumstances that come up all the time. Oh, Yeah---what
a car!
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