How do you R&R tensioner spring and pulley? - PeachParts Mercedes-Benz Forum

Diesel Dan · #1 04-15-2008, 03:01 PM

Hey folks,
I've got a squeaky serpentine belt that did not stop squeaking upon replacement. I have about 1" of deflection in the belt. I'm assuming the next step is to R&R the tensioner, and maybe also the pulley, which seems to be slightly askew, forcing the belt to ride a little off center towards the front.

Can anyone tell me how to do this on the '87 300D? It's really hard to see what is going on in that dark, cramped spot. Will I have to remove any other items to get to it? Like the fan, or radiator? How do you remove the tensioner and pulley?

Thanks,
Dan

Bill Ladd · #2 04-15-2008, 03:52 PM

Quote:

Originally Posted by Diesel Dan

...and maybe also the pulley, which seems to be slightly askew, forcing the belt to ride a little off center towards the front...

That's not very good news. Your timing chain cover may be cracked. See pictor of GSXR's busted one here --

First thing you probably want to do is take off the fan and shroud and then remove your radiator to get a better look. It's all pretty easy stuff.

Oh, and get either a CD manual from MBCA or online somewhere or a paper 602/603 engine manual, 126 chassis and body manual and Electrical troubleshooting manual. You will be very glad you did.

TMAllison · #3 04-15-2008, 04:06 PM

Could also be the idler pulley bearings or the tensioner pivot arm is worn.

The inside of the pivot arm has a sleeve which wears.

connerm · #4 04-15-2008, 04:21 PM

Could be a belt made by Continental.

sixto · #5 04-15-2008, 04:43 PM

The belt has been replaced so I'll assume you can do that.

With the belt off, try to determine if the skewness is caused by a wobbly idler pulley or tensioner arm. Even if the tensioner arm doesn't wobble, check that it pivots smoothly. As the bearing wears, there will be detents or a clickiness to the pivot motion. That's reason enough to replace it.

I've replaced the tensioner arm in an SDL without removing the fan but there was a lot of luck involved. Remove the fan unless you enjoy puzzles.

If you have any reason to pull the radiator, do so, but it's not necessary. If the radiator stays in place, cover it with something like thick cardboard for protection... the radiator's and yours!

If you're really lucky, the water pump will have a big rib at the top which extends almost to the pulley flange. That will allow you to use a 3mm pin or stiff wire to hold the pulley while you loosen the bolt that goes through the clutch. That bolt takes an 8mm hex tip. There's a special tool stubby 8mm bit available but I use a hex key and slip over the long end a deep 10mm socket on a breaker bar. If your water pump has a small top rib, you probably won't get a pin to hold the pulley. You'll need a special tool to grip the pulley so it doesn't turn. Here's a pic pilfered from gsxr's collection - http://www.w124performance.com/images/tools/OM60x_serp_belt_tools.jpg

With the fan out, pop the plastic cap off the tensioner pulley then use a 6mm hex bit to remove the pulley.

Move the tensioner arm so you have access to the tensioner shock lower bolt. Use a 13mm wrench or socket to remove the bolt.

Pop the plastic cap off the tensioner arm pivot. Use a 12mm hex bit to remove the tensioner arm. It might be tight. Heck, it should be tight. Spec is something like 70Nm (injector tight) plus some sort of sealant since the hole in the timing chain cover goes through to the timing chain; i.e., the oily innards. There should be a thick washer between the arm and the timing chain cover. Many get tossed with the old arm and new arms don't come with the washer. I suspect 603s prone to belt derailment are missing this washer.

Installation is the reverse of removal but confirm tightening torques and sealant specs since I have a bad memory. It might be easier to get the shock on the tensioner arm before the arm goes on the engine.

Check the shock for continuous resistance through its stroke in both directions. Check also the Heim ends. Loose Heim ends can cause a scary knocking sound like a bad main or rod bearing.

I don't think there's a top and bottom end to the spring.

Sixto
87 300D

Bill Ladd · #6 04-15-2008, 04:49 PM

Right on. I should have clarified to remove the radiator if a timing cover replacement was needed. I imagine it can be done with it in there, but I wouldn't want to try it!!

Thanks for writing that for him, Sixto, I'm too burned out right now.

Diesel Dan · #7 04-16-2008, 10:08 AM

Thanks Sixto, that was very helpful information. Now I feel prepared to launch into it!

Diesel Dan · #8 05-05-2008, 03:21 PM

After many frustrating hours, I have loosened the big allen bolt that holds the tensioner arm on, but as I unscrew it, the arm is blocked from coming off by the fan pulley, no matter what position I try to wiggle it into. I see on my new tensioner arm there is a circlip that, once removed, may allow the tensioner arm to move on the shaft. The new one didn't budge even after removing the circlip, but perhaps since the old one is looser it will? Anyone else have this experience? Will I have to remove the fan pulley to do this job? How hard is it to remove the radiator in this car? Does anyone have a link to a DIY?

Thanks!

Bill Ladd · #9 05-05-2008, 03:36 PM

Quote:

Originally Posted by Diesel Dan

After many frustrating hours, I have loosened the big allen bolt that holds the tensioner arm on, but as I unscrew it, the arm is blocked from coming off by the fan pulley, no matter what position I try to wiggle it into. I see on my new tensioner arm there is a circlip that, once removed, may allow the tensioner arm to move on the shaft. The new one didn't budge even after removing the circlip, but perhaps since the old one is looser it will? Anyone else have this experience? Will I have to remove the fan pulley to do this job? How hard is it to remove the radiator in this car? Does anyone have a link to a DYI?

Thanks!

I'm pretty sure I had to remove the pulley to get the tensioner off. Not too tough a job at all. Same with the radiator.

Let's see if I remember correctly --

Unclip shroud and move it out of the way as best you're able.

Lock off the fan thermostat as Sixto described above.

Remove fan and thermo with 8mm allen wrench.

Remove shroud.

Drain radiator (on bottom at one of the mounting divots in the front crossmember or via the bottom hose), remove radiator hoses, unclip and remove radiator.

Remove the (three or four, I can't remember and ain't in front of my car right now) pulley bolts.

Tap off the pulley.

I think that's it or close enough that you'll be able to fill in the blanks. Anyone want to add/change anything here, please feel free.

Good luck and let us know how it's going.

BTW -- that bearing circlipped into the tensioner is interference fit -- has to be pressed on and off.

Bill Ladd · #10 05-05-2008, 03:39 PM

Hey -- I'm pretty sure I removed the tensioner to replace the tensioner shock absorber without removing the radiator.

In fact, I'm positive I did. My vehicle's a 126 though -- the 124 arrangement up front may be tighter.

Diesel Dan · #11 05-08-2008, 12:35 AM

Victory is MINE! I finally wrestled the radiator and fan/shroud out and was able to see what the hell was going on in there. It was then that I realized that I could pull off the tension roller and move the tensioner arm enough to clear the blasted fan pulley. At least I didn't have to pull that off!

So now that I've got the radiator out, what else should I do? My A/C compressor is shot, so maybe now would be a good time to replace that. Also, I have a clear view of the oil pump, so I'll have to research if I've got one of the "bad" models, or a good one. I suppose I should clean the engine. What else?

sixto · #12 05-08-2008, 12:36 AM

Oil pump? Maybe you mean vacuum pump.

Sixto
87 300D

Diesel Dan · #13 05-08-2008, 12:37 AM

Oops! Right, I meant vacuum pump!

Diesel Dan · #14 05-12-2008, 10:43 PM

Hey folks - me again!

I'm getting ready to put things back together, and I'm wondering about three things right now:
1. Do I need to use some sort of sealant on the tensioner arm bolt? If so, would high temp RTV silicone gasket maker (the red stuff) work? I happen to have some handy.
2. What is the torque on that bolt? Someone said 70Nm/53fp - is that correct?
3. Someone also mentioned a washer that is supposed to be between the arm and the engine. My old tensioner did not have one, but it never threw a belt. Is it possible that it's now just built into the arm? Or is there definitely a separate washer I need to buy?

Thanks!