Gents,

The one in green is the same part number ( guide pulley), being on different location.
Since 100% they are the same, the tightening torque has to be the same, but no, someone at MB screwed-up and 25 vs 35 Nm a 10 Nm difference is not a joke....it is BIG.

So, if you were me, which value would you use ?



I shall show photos to make it clearer.




Item 6 - plastic pulley removed, only the bolt + washer placed there.




Item 7 and carrier ( I wrote as B)



So... ? What's your take on this ?


==========================

Why I am into the guide pulley and tensioner ?
I am replacing all 3 "consume-able -" spinning + tension components ( WIS diagram item 6, 7 and complete #2 ) because my serpentine belt is showing sign of plastic pulley already not aligned properly.
So might as well replace tensioner too, to get virgin tension. Odometer today, 36,000KM only and these 3 are that "old" too, 36K KM.
This belt is new as of 20,100KM Nov 2019. So only 16,000KM. I limit belt to 5 years max.

Red zone, the bad one







Do you want to know which component is the culprit ?


New unit, its bolts sit so tight inside the pulley bore and you can't push it out with your finger unless you try super hard ( nope I did not try pulling out the bolt)....because the black plastic insert is still dimensionally 100% normal.
Good fit, meaning perfect alignment is possible.

The 36,000KM old unit, flip the guide pulley with the bolt head down and bolt + its big washer will drop to the floor. Yep , the plastic insert has been "consumed" aka thinned down...been raped, gang-bang-ded.

What a waste of money, the bearing is still good. The plastic pulley itsefl its grooves and physical condition is still good.
Only that stupid plastic black azz-hole insert is the weak link.

HHmmmm too much sausage and beer probably during the design phase... LOL

 

Well.... spring at tensioner weakening already.


Tensioner, to counterclockwise it a tiny bit to remove tight tension to belt.
OLD = 35 Nm
New = 40 Nm

Tensioner, to hit full stop ( spin counter clockwise ), spring maximum power.
OLD = 56 Nm
New = 71 Nm

Torque values using AC Delco https://www.acdelco-tools.com/index....product_id=208

Must replace the serpentine belt again, damn. Waste money.
I need belt side new and nice all black to detect if someday the pulley/s mild out of whack again.


BTW......I use 35Nm , not 25Nm.
The flying sourcer shape washer is pushing the bearing inner race, so no harm to any plastic.

 

I knew the tensioner was the money maker but did not know its spring was actually loosing strength.... how nice is that!!

The spring looses it's preloaded springiness by way of heat cycles softening the mild steel heat treatment. ✌️
As the tensioner begins to flap back and forth it carves itself a groove that traps the pulley arm.

This stops the pulley from applying necessary tension to the extra long belt.

Without proper tension the multi-grooved rubber surface gets worned through then the belt slips over A/C compressor, burns up and falls apart.

Pump stops > engine overheats > $$$$


Plastic pulleys...: ✔️
Using plastic idler pulleys instead of steel helps insulate the inner bearing from the heat generated when the belt slips over the A/C pulley. Not bad after all.
Idlers are only used to stop side-wobbling over long distance, no power is involved.


The only way to deal with belt issues is a complete kit because the belt life matches that of tensioner itself.


[
I saw how Tasos carefully micro measures the work done at machine shop:
"You cant expect what you cant inspect!!"
]

 

I think there is at least 40Nm of pressure on each side of the plastic pulley guide region the poly belt pass thru. This is the tensioner sping tension...right.
Like a side loading. I guess that is what ate the inner plastic insert.





The poly belt is awesome.
Imagine the equivalent kilowatt of drag it must handle.
01. Alternator at 200A if full load is 2.4kw plus 10% loss
02. HVAC compressor, easy 1.2 Kw
03. Coolant water pump, easy 0.5kw

Let say average use is 2.5kw...... that is alot.

 

Wanna hear a joke ?
The new belt also has the white cord visible at some region.

It is how they make it. Wide belt and cut cut into smaller pieces, so the white cord which is the strenght layer most often is visible.

Anyway, I decided to do the 2 guide pulleys and 1 of tensioner because it is visually obvious, the minor wobble.


I extracted 2 frames and made a GIF for easy viewing.

 

attached WIS on Serpentine/Poly belt

 

I want to confirm the wear pattern if indeed from side loading.

Steel bearing inner race , internal diameter 16.99mm






Yes , the wear pattern is from side loading














I can only measure B to B and not B to mid center. But overall the "consumed" plastic is traceable, albeit I do not know if B1 or B2, which one actually has more wear ?










Perhaps this azz-hole plastic insert which is like a bushing/bearing can also be a safety bearing when and if the steel ball bearing seized.

 

@S-Prihadi, did you have to remove the intercooler to replace the tensioner? If not, I assume just the trans/turbo coolant reservoir and some of the evap valves at the front gives sufficient space for that and the 2 pulleys? Looking to replace your #6 pulley, possibly waterpump, and the serp/poly belt with minimal effort

 

On M276.8xx 3.0 Turbo, anything you touch related to the serpentine belt region, the aftercooler must be removed.
Its not that difficult, but a hassle.

If you find pulley #6 bad or going bad, replace the other pulley and also the tensioner. These Trio are the same life time.