Belt squeak - overtightened tensioner?

[Madsbkelo]

Hi forum,
I am new to this forum, but have really got a lot of information already.

When cold starting the car, sometimes the belt is squeaking and in other occasions.

I have a 1992 M119 with the manual/1st version tensioner and was looking into if this could be the issue. For me, the tensioner looks newer than the other parts, why i think it has been changed before. To my surprise, it looks overtightened and thinking this could be the case? I have attached photo of the belt.

I can read on this forum, that the manual/1st version is more likely to be wear out.

/Mads

 

[gsxr]

It's unlikely the tensioner could be over-tightened as much as shown in your photo.

The plastic pointed can move separately. You'll need to try re-adjusting, by loosening the center bolt & adjusting rod, and verifying the pointer is located correctly with zero tension. I expect you'll find that after loosening, the pointer will NOT go to the zero position.

Better yet, also remove the tensioner from the engine and bench-test to make sure it hasn't failed, where the rubber bushing rotates within the housing. If failed, replace with new OE/Genuine only. All the aftermarket tensioners seem to have a very short lifespan.

Click here for the FSM procedure, job # 13-3420. Additional info here. Search the forum for additional discussion about the tensioner.

BTW, welcome to the forum!

 

[Madsbkelo]

Thanks - will definitely do that.

I will try to spin some of the other pulleys to see if one of them is due to the squeak.

 

[geraniumtr]

Dave, I've never seen a close up photo of the early M119 tensioner. Differs from my early M104 one in that the pointer on mine sits on top and there is a sloped triangle embossed on the tensioner to clearly show loose/tight. You tension the belt so the pointer is roughly in the middle. I don't see such markings in the photo.
I also hope the owner did not turn the adjusting rod without loosening the tensioner bolt.


Regards,

Peter

 

[Madsbkelo]

I will look into the tensioner this weekend. Do you know what the length of the belt should be? The current is 2525 mm which is 2 mm more than the length I Can look up.

 

[gsxr]

I will look into the tensioner this weekend. Do you know what the length of the belt should be? The current is 2525 mm which is 2 mm more than the length I Can look up.

Is the car a 500E?

On close look at your photo, you have a 6-rib belt and pulleys with an 8-rib pulley tensioner. Something here isn't matching.

Normal 8-rib belt length on a 500E is 2465mm.

The 6-rib belt is longer due to a different tensioner design and also, I believe, a slight difference in one or two pulley diameters - not positive about this though.

 

[Madsbkelo]

This is a 500SL with the M119.96x engine.

Could be that the tensioner has been replaced to an 8-rib by mistake. Do you conclude that from the tension pulley being significantly wider than the belt?

 

[gsxr]

This is a 500SL with the M119.96x engine.

Could be that the tensioner has been replaced to an 8-rib by mistake. Do you conclude that from the tension pulley being significantly wider than the belt?

Ah, that explains it. The 129.066 uses a 6-rib belt in different lengths. EPC screenshot below.

Should be 2523mm long with catalysts (due to smog air pump)
Should be 2176mm long without catalysts (bracket/pulley in place of pump)

Correct tensioner pulley is 601-200-07-70. Your pulley is wider than normal, but I don't know if the diameter is the same or not.

You still need to release tension and see what's going on there, along with re-setting the plastic indicator per the FSM procedure.

 

[Madsbkelo]

Thanks! Really helpful.

What is the correct diameter of the tensioner pulley? When I look it up, it looks grooved om the pictures, which confuses me since it runs on the back of the belt?