Any suggestions on how to keep the tensioner adjustment mechanism (as shown on the attached drawing) from going down into the hole in the bracket when trying to put the tensioner into the belt slack position? I have about come to the conclusion that probably the best way to slip the belt on is to use a pry bar to pry the pulley back when I install it instead of messing with this.
thanks

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Jim

Here is the shot. Notice how the adjusting nut portion has screwed down into the opening that you install it through.

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Jim

I'm not sure why that's a problem. When you get the belt on, the nut will pop up against the retainer. In fact just getting the tensioner in place will probably put the nut closer to where it should be.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

I agree, it shouldn't be a problem. If you've loosened the tensioner center bolt, you should be able to rotate the tensioner by grabbing the idler wheel and pulling it toward the slack position, which will also push the adjusting nut up into the hole again somewhat.

When you first loosened the center nut and backed off the adjuster nut, did the tensioner body rotate back on its own as it released tension on the roller? If not, the tensioner may be kaput!

Gary

The only problem I've had is eventually the tensioning rod slips when getting the belt fairly snug, but not quite as snug as one would like. Ended up replacing the rod itself; not the whole unit.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

I did not think about the belt pulling it up. I have just gotton all the accessories mounted on the drivers side (water pump, ps pump, tensioner, etc) and will be installing the cyl head/intake this weekend after which time I will be putting the belt back into place. If ya'll don't mind, what exactly is the proper procedure for setting the tensioner and installing the belt? When I was taking it all apart I just used the prybar to pry the tensioner back far enough to remove the belt. Phalcon the tensioner seems to be in good working order because it is really hard to "swivel".
thanks

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Jim

I've done this a half dozen times or so - just went through this replacing an alternator.

There's a belt routing diagram in the owners manual and the MB maint. manual. It's easier if you make a loop to shorthen the belt and work from the center pulley routing around. I always end up at the PS pulley(last pulley to slip belt on). Make sure the belt grooves are in the pulley tracks. I then put a 6 point 27mm socket on the end of the crank pulley and rotate clockwise as seen from the front and thoroughly examine the tracking of the belt at each pulley.

Once I'm sure that's ok, I start tightening the tensioner adjuster clockwise with a 13mm socket until the belt is good and snug. Finally I tighten down the 19mm that's buried in between two of the upper pulleys.

Piece of cake.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

The problem is not that the tensioner gets loose, but that it takes a "set". The tensioning medium is rubber and after prolonged exposure to tension and heat over many years the rubber does not rebound fully anymore. When the center bolt is tight it will always be difficult to swivel. The thing to check is the unloaded resting position of the idler wheel relative to the machined flats on the center hub on the back of the unit. The best way to do this is to take your old tensioner in to a dealer and ask them to pull a new tensioner off the shelf so you can compare them. If you have to replace it FastLane will have a much better price than the dealer.

Read this earlier thread where I've included some pictures explaining what to look for:

1993 300se belt tensioner adjustment

Hope this helps

Gary

Jim:

I'd pretty much figure on replacing the tensioner.

Correct procedure is to loosen the center bolt and then unscrew the adjusting nut to release the tension. You can leave it loose while doing the head, etc.

Going back on, leave loose and install belt except for the AC, then pull the belt out and push the tensioner pulley to relieve the tenstion -- the shock tends to extend if it's any good and shove the tensioner all the way tight.

I though I had the wrong belt when I did the water pump on the TE a while back, it pulls up so bad. Hans laughed at me, he forgot to tell me that little trick.

Once the belt is on, use the adjusting nut to pull the tensioner around till the pointer is near the top of the "ramp" cast in the tensioner body, then tighten the center bolt.

The bad part here is that the rubber is used as the spring in the tensioner, and looses is resiliecy (sp) with age. Chances are you won't be able to re-tension correctly -- tensioner should move back with the adjusting nut loose to the line in front of the ramp. If it doesn't, you need a new tensioner. Attempting to use the old one usually results in the adjusting rod going too far over on the exccentric and getting in a bind -- usually breaks.

Tensioner is about $150, I think. PITA to replace, too -- bracket in front has to come off.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks everyone.
I will look into installing a new one when I go to button everything up. It is going to be about the only part on the front of the engine that is not new if I don't replace it. My plans are to go ahead and install the cylinder head/intake manifold this weekend leaving the tensioner, belt, fan and fan clutch for last.

This is the first tensioner of this sort I have messed with. Personally, I think it is kinda a poor design. Why couldn't it have been designed where you just put a 1/2" drive breaker bar in a hole and turn it part way to relieve the tension?

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Jim

Jim:

I don't know about poor design, since it seems to work well, but it is certainly a perfect example of German love of complexity. I greatly prefer the tensioner on the 603 -- almost exactly what you were wishing for!

A bracket, a spring, two bolts, and a shock. Nice and easy, except you have to pull the fan clutch to replace the shock -- the bottom bolt is about three threads too long to remove with the pulley on. I know, I tried.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Jim:

Looked over your post again, and the direct answer to your question is to thread the adjusting nut on the threaded rod before attempting to install the belt. The belt tensioner shock tends to extend, and if you don't, the bolt falls through the hole.

You will still have to manually shove the tensioner pulley to the correct position. I used the belt to help -- pull outward by the AC compressor until it's loose enough to go over.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

This whole 103 tensioner deal puzzles me as much as calling for the chains in football. It seems that final tension depends on where the pointer is when you start.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Sixto:

It indeed does depend on where the pointer was when you started. That means, of course, if it doesn't point to the correct "start" mark loose, it won't tension properly and you will bend or break the tensioning bolt if you try.

I'd strongly prefer a steel spring.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

You can put the "pointer" anywhere you want when putting this system together. I picked up a new tensioner at the dealer today and will put it on after I get the head on (the tensioner system makes a cylinder head rebuild look easy by now:0). I will get back to the tensioner probably around next Wednesday or so.

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Jim