Replacement of serpentine tensioner - Please help

Check the tensioner wheel... if it rattles as you spin, you should just buy the wheel and replace it... very easy.

The tensioner has two part... one is at the tensioner... in front that holds it in position...

The other part is up on top of engine... brass hollow nut thing to tighten up the tensioner... if this part is loose... you might have broken tensioner rod... you can tell if you can just pull it up.

In any case, you need to loosen up the upper tensionser adjustment nut... then fish the new belt in... and tighten the upper tensioner and finally the lower tensioner bolt to lock it in.

Thanks, Tiger, for your quick response.

The tensioner itself is held by the lower bolt, as you stated. After removing the old belt, I tried to move the tensioner by hand and it did not offer any resistance to my effort. Then I assumed that the internal spring was broken and bought a complete assembly that includes the tensioner wheel, lower tensioner bolt, adjusting rod, the hollow nut, a plastic position indicator and a bracket. The new tensioner's spring is firm and robust as it should.

So, I decided to remove the old wheel assembly and replace it with the new one. This is where I stand right now in my DIY project: Stuck.

I have not figured out how to REMOVE the bad assembly without taking off the AC compressor pulley or who knows what else.

If I ever get the new assembly in place, the belt adjustment procedure is a no-brainer.

Thanks again,

Hernando

I replaced this tensioner in my 1986 190e 2.3.

very simple really. Remove the big bolt (22mm?) that goed through the front of the tensioner. Unclip the little shock at the bottom of the tensioner. Release the tension adjustment from the big tall nut at the top of the timing case...

That's it. then it all comes out, although it does take a bit of patient wiggling to extract it.

Good Luck, Marty

PS No need to remove any AC or anything else.

If you only had the center bolt holding it on then one of two things has happened:

1) you have never had it replaced 2) you never brought the car back [in the USA] to the dealer for all the free upgrades for the A/C in the late 80's, one of which was a modified belt tensioner.

The updated and now replacement tensioner has a support bracket over the front of it. The center bolt goes thru it. 3 more bolts hold it on and you have to remove the power steering pump pulley to get to one of them.

99 out of 100 102 engine tensioner failures is the center hub rubber shifting. You will run out of adjustment threads long before the tensioner gets the belt even snug much less tight. The center hub actually moves 90 degrees over time. The center hub is the piece with two flats on it that the adjuster arm sits on. Compare a new one with a bad one side-by-side and you will see the difference in positions.

Thanks, Marty, thanks! Here I was all worried and confused about the extent of the job and you came to my rescue with your knowledge and experience! Your help is very much appreciated.

Hernando

upgrades for the A/C

of it. The center

steering pump pulley to

You will run out of

tight. The center hub

flats on it that the

will see the difference

Thanks Karl and Marty for your thoughts.

Just like President Reagan used to say "here we go again..." Thanks for the additional info on the replacement of the tensioner.

1) I bought the car new so I know that this is the original tensioner. It was never "upgraded."

2) To the best of my knowledge the MB dealer did not upgrade for the AC and tensioner assembly.

3) The tensioner replacement kit does have a NEW bracket, a threaded rod, a plastic position pointer, a new center bolt with a 22 mm head (the old one has a 17 mm head).

4) As a matter of fact, I pointed the difference in head sizes to the MB Parts associate and he told me that MB had upgraded the tensioner assembly. Now that Karl explained the configuration of the new tensioner, I understand why there is a NEW bracket.

5) Karl mentions the upgrade for the AC issued in the late 80's. If I replace the tensioner with the new one without also upgrading whatever was supposed to have been replaced in the AC, will it work? Or the upgrade for the AC is a prerequisite?

6) The description of the failure caused by the center hub rubber shifting matches exactly the failure mode of the original tensioner. I ran out of adjustment threads trying to adjust the belt tension.

I apologize for the lengthy details but I feel that we all have to have the complete picture before I attempt to finish the job.

The A/C upgrades included: A new 2 piece manifold hose instead of the one piece, replacing the green pressure switch on the drier with a red one [this turned the fan in front of the condenser on at 275 lbs instead of 325], adding seals around the condenser so all the air went thru the condenser and not around it, changing a relay in the fusebox and adding a wire to the 3 legged temp sensor so the engine fan will lock on when the aux fan comes on. These upgrades made the system work very well.

free upgrades for the A/C

front of it. The center

steering pump pulley to

shifting. You will run out of

less tight. The center hub

flats on it that the

will see the difference

Thanks again, Karl, for your help and the amazing knowledge that you shared with me.

I just came down with pneumonia and won't be able to work on the car for a little while.

Best regards,

Hernando

Karl wrote:

piece, replacing the green

the condenser on at 275

thru the condenser and

legged temp sensor so the

system work very well.