Serpentine Belt and
Tensioner Replacement

This is not my car but a 91 Stealth RT / TT that I did this on so if you see Pearl on the car,
the answer is no,, I didn't paint my car. Way back when I did my Upper Tensioner I did
not take photos so I never did a page on it. You really like my mindless dribble before
each repair job don't you?? Oh well,, makes it more personal,,

Ok, here we go,,, on to another fine job

First off we must jack up the car on the drivers side and remove the front wheel and also
the wheel well skirting. If you haven't removed the wheel well skirting before you are in
for a treat. Bolts I am sure I do not have to tell you how to remove or you shouldn't be here,
so, here are just a couple notes and two photos on the subject.

This first photo is of those little plastic screw / expansion fittings Mitsubishi loves to use.
At first I thought,, how chincy,,, but considering they have held my wheel well skirts in for over
100,000 miles, I guess they work pretty well. That said here is the photo.

These little babies do a pretty good job of holding things together. They are however sometimes
difficult to remove without destroying them. Here is a hint. Although they will screw, many times
you can screw forever and they just don't come out. Well, a little tiny screwdriver prying up between
the screw head and flange head while turning will usually start them on their upward journey with
sometimes a little frustrating coaxing. To replace them is a snap, because you just make sure the
screw is far enough out so the back wings can go into the hole and just press the screw right in
As it goes in it flares out the wings and holds it in the hole. Holding it by the screw while stopping
the screw from going in is the best way to coax it in the hole
Ok, on to the next pain in the butt about the wheel well shrouds. Right behind the front bumper
there are three screws that have clips attached to plastic on the bumper. When unscrewing these
from the clip, most times the clip will seem to break right out of the cut out in the bumper and
from what it looks it is shot. Not true. A little WD40 on the clip and holding it back while unscrewing
the screw from the clip with take it apart. Now clean up the clips and remove any debris from the
clip and it should slide right back on the cutout in the bumper. In the photo below, when I
attempted to unscrew these bolt all three just came right off the cutouts. They are shown
cleaned  up and reinstalled. Also clean up the screws so they go back in easily. They all reheld
the skirting fine and tight.
 Yuck,, what a dirty mess,, guess you guys can tell this isn't my car,,,

Ok, enough of the Wheel well Skirting, on to the Tensioner and Belt Replacement
Shown below is the lower tensioner. This happens to be the new one, but just imagine it
being the old one and the old belt is still on the car.
Using a #14 Metric Socket on a 3/8 drive, place the socket on the center bolt and using a
hammer strike the sockets drive handle a couple times to break the bolt loose. This is the
easiest way and simulates an air impact wrench. I do it all the time.
Just loosen it a couple turns. The reason for this is that with that bolt tight, the adjustment
for loosening the tension with the top bolt seen peeking out at the very top of the tensioner will not
loosen without that bolt loose. Tightening it when finished locks in the tension  so it will not move
even if the tensioning bolt loosens. Both upper and lower tensioners are shown here
The upper larger one lists for $45 and the lower smaller lists for $91,, crazy huh??
Tallahassee Mitsubishi has them a lot cheaper for 3SI members

Behind the above tensioner is the tensioner adjustment bar for adjusting the belt tension and
you can see better how it works. You can also see why we have to loosen the center tensioner bolt
first to allow it to slide up and down the surface.

Now with the center bolt loose we can place a #12 socket on the tensioning bolt on top of the
slider bar and loosen the tension of the old belt. Counterclockwise would be the direction for
loosening as it would lower the slider and move the tensioner away from the belt
Once the belt is loose enough to slide off the tensioner it can be removed by turning it sideways
up near the alternator to clear the tight places
If you also need to replace the top tensioner or only the top tensioner, you must also remove that
one using again a #14 socket with a 3/8 drive narrow driver. It's a tight fit and close to the body,
but it will work. This is why we must use a 3/8 drive handle for clearance. Once again use the hammer
to strike the handle to free the bolt
You will be laying on the ground for a lot of this work and also under the car, so you better have the
car on jack stands
Shown below is the entire Serpentine area. The Serpentine runs the Alternator shown center left and
the air conditioning compressor shown lower left using two tensioners. The top and larger one is
stationary and screws in the top center bolt hole. The lower smaller one is actually the one that provides
the tension. On an engineering note, I see no purpose for the top tensioner except something to go bad
I would suppose they put it there to prevent flop of the belt over the distance from the alternator to the
crank shaft pulley. The crank shaft pulley is shown on top just right of center. Not knowing much about
them I would guess this is where an under drive pulley would go, but they don't make much sense to me

Shown below is another view of the tensioner mounting locations

Shown below is the old tensioners and New Tensioners Side by side
Note the design change with the advent of new metal pressing techniques
They are also lighter weight and missing the rivets holding together the older
ones halves for holding the bearings
Also take note and enlarger the photo to see the serpentine belt deterioration

Here is a view of the old and new from the back side. One can more easily
note the lighter weight stampings between them

On a note: (below photo)
The original tensioner had a bearing slinger washer. The new one does not require this
washer and in fact can not be used as it will interfere with the clearance and prevent the
tensioner from rotating, burning up your new belt because it would not rotate
Just use the bolt and not the washer

Next photo is full size and shows the Serpentine routing. The easiest way to install it is to install
both tensioners as needed but do not tighten the lower one so it can be adjusted.
Route the serpentine around the whole assembly, going on the outside of all the pulleys making sure
the serpentine is in the grooves properly and not hanging over either side of any grooved pulley
Push the serpentine up on top the lower tensioner first, then pull the serpentine down under the top
tensioner by relieving the bottom tensioner as necessary (turning the tension adjusting screw
counterclockwise) enough to get the serpentine under the top tensioner
Once the serpentine is routed correctly and all areas checked turn the lower tensioners adjusting
screw clockwise thereby raising the tensioner up and pressing against the serpentine till the belt is very
snug. The belt should flex about 1/4" when pressing very hard on any span between pulleys or tensioners
You do not want to over tighten it because that will affect bearing life of your alternator and air conditioning
compressor not to mention the tensioners, but it wants to be pretty snug
Start the car and run for about 10 seconds. Recheck tension and routing.
If all is OK, your final will be to tighten the center bolt on the lower tensioner
Again here I use a hammer to strike the drive handle. I use a small ball pien and strike it about 10 times
with not real hard blows,, similar to driving in a 10 penny nail
Some of you technos might wish to use a torque wrench and tighten to specs, (36 ft Lbs) but I have been doing things
like this so long it isn't funny and maybe I just have a feel for what is tight because I never have any problems
I rarely ever use a torque wrench, but I do have one 1/2 " drive and usually it's to big to get in anywhere
much less this top tensioner with it's minimal clearance

That about wraps it up guys,,, all that is left is reassembly, reassembly
once again,, have fun

Part Numbers

Serpentine Belt - MB879764
Tensioner Pulley - (small lower) - MD318474
Idler Pulley - (larger upper) - MR360357 (Replaces part # MB630326)
 

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For questions send e-mail.   Last Update 6/15/00