300E - how long does a fanbelt tensioner last
 

Tackling some noise in and around the fanbelt, I found worn bearings in the fanbelt pulley and the guide pulley, which I will be replacing. I also found that my fanbelt tensioner was at the limit of adjustment and also needs replacing.

Checking back thugh my records, I find that this item (124 200 08 70) was replaced in October 2003 by the dealer shortly after I bought the car. Since then the car has covered around 20,000 kms.

Surely this can't be right? I can't believe that a fanbelt tensioner would need replacing that often.

Anyone have any experience with this?

How long...
 

Hallo Simmo,

On my 1990 W124193 ( 603 turbo ) it's lasting 375000 km now and still in good shape.
In winter at temperatures lower than 0° C, the belt makes some noice.
Than I put some chalk on the inside and the noice is gone.
In your case it's certainly not normal that the tensioner is gone that fast.
Let us know about your sollution when found...
Good luck,

Danny

My 1986 300E was sold in 1993 with 116K miles on it. No pulley/tensioner changes. My 1993 400E has 128K on it. No pulley/tensioner changes.

You said that it is at the limit of its adjustment. I think you misunderstand how the tensioner marks are used. They are used when tensioning the belt and then do not change until you loosen the bolts again.

When replacing the belt and/or tensioner, you should always do two things; follow the instructions to get it tensioned correctly and spin all pulleys and accessories to check for roughness before putting back together.

BTW, my original tensioner lasted about 200,000 miles.

Good luck,

replacing cog tensioner belt on 92 300-E
 

I would like to know the proceeder for removiing and replacing the cog belt and tensioner on the 6 cylinder 1992 300-E? does nay one have any short cuts to doing this job. Als o what tools do I need?

Thank You
Krwaxbz

You need a 19 mm socket and a 13mm socket. If you are removing the belt for any reason, you need an 8 mm Allen and something to hold the fan clutch (a coat hanger wire for older (pre 89?) models, strap clamp of some sort for later one.

Before removing tension on belt, note the small pointer (usually red plastic I think) that points to the "ramp" cast into the tensioner body. You will need to watch this pointer while loosening the tension.

FIRST loosen the 19 mm center bolt on the tensioner. This bolt holds the center of the tensioner firmly in place, and if you attempt loosen the tensioner with it tight, you will only break the link.

SECOND, while WATCHING the tensioner body, unscrew the 13mm "bolt" that sticks up behind the belt near the head. If the belt comes loose and the markings on the tensioner body DO NOT move back to at least the start of the "ramp", the rubber in the tensioner is shot and it must be replaced. You must watch while loosening, as when you pull the 19mm bolt, the pointer will fall off, it is splined and fits anywhere. It will stay in place if you do not remove the tensioner though.

To remove the tensioner completely you must remove the bracket across the front I think (hard to remember at the moment), maybe not. Some one who's done this more recently will remind me. Tensioner comes right off with the 19mm bolt out.

The bolt that actually rotates the tensioner body is linked to a d-shaped ring that goes on the back of the tensioner body, make sure you know which way it goes back on or it breaks off when you attempt to tension belt.

Going back in, install the ring on the back, put the bolt up through the hold with the round side of the "nut" up, install the pointer so it is at or before the "ramp" mark or where it was when you loosend it (old tensioner), or at the line before the ramp (new tensioner). Snug the 19mm bolt up a bit so the pointer won't fall down, then install the belt (you will have to push the shock over to get the belt on the pulleys), then use the small bolt to pull the tensioner up til the pointer is at the "tall" end of the "ramp" mark. Tighten 19mm bolt.

Not hard, but usually messy from the "normal" front of engine oil leaks.

Peter

R&R cogg belt 300-E
 

I appreciate your instructions however I am having a hard time visualizing what you are talking about. Do you have any photos of steps you take for this proceeder. My car has only 38,000 miles on it so I do not suspect too much of a problem with woren out parts. Also how do you remove the fan shroud and put it back?

Thank you.
Bob Geco

Fan shroud? Sorry to be rude, but if you cant get the fan shroud off. . .
Who knows, if it is the same as the 126 I am working on, there are two clips at the top and two tabs at the bottom that slide into slots in the rad support down below. Go do some crawling around under the car.

Great description psfred, I will file that away.

Just another "thank-you" to psfred. Excellent description. I have to replace that tensioner/shock thing (rattling) and will replace belt and tensioner at the same time (89 300CE, 174K). Your description will be valuable. If I buy the beer will you come and supervise?

I would like to add that getting the tensioner properly tensioned is one of the keys to its longevity: Too tight and the tension stresses the bearing and bearing assembly, too loose and the motion of the belt seems to tear the inner rubber section.

I would suggest following everyone's advice and become familiar with how the setup works.

Regarding the bearing in the idler wheel, make sure the plastic dust cover cap is in place. If missing it will allow dust, dirt and water in and it won't last long at all.....

Haasman

dwest:

Sure, but it'll take me a couple weeks to get through the snow, I'm out of practice down here is springtime land (the daffodils are blooming here).

Bob:

If you are new to working on these cars, I recommend the service CD available here on Mercedesshop, it's most of the factory manual and has very good diagrams. You will need to already know mechanic work, though, as the instructions are often "remove, replace" with no details....

The fan shroud is indeed held in place by two spring clips, on the top corners. There is a set of "teeth" on the radiator support and on the shroud so you can adjust the height to center it on the fan. It will NOT come off with the fan clutch and fan installed, so just hang it back out of the way. The fan clutch is held to the bearing (the water pump is above the PS pump, not behind the fan) by a single 8mm allen head bolt in the center. On the bracket, there is a pair of raised bumps, into which one inserts the factory tool (or some heavy wire, bent out at about 45 degrees on the end) so that it will fit into one of the holes on the back of the fan clutch while held in place by the tow bumps. This holds the clutch so you can unscrew the bolt. Pretty easy.

The tensioner is below and to the driver's side of the fan bearing, it's the only 19mm bolt up there. The tensioner pulley is the one the belt goes around "backwards", easy to spot. The tensioning bolt sticks up almost straight right next to the head, has a flanged nut underneath the bracket there, 13mm end on a long, straight shaft.

The CD diagrams make this pretty easy.

Peter

I can confirm that its the inner rubber that is shot on my tensioner. Will pay attention to tensioning it correctly when I replace it. Right now the unit has two holes drilled through to the inner core and two bolts glued in to provide some tension. messy but effective until I change the unit this weekend