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First my apology if this has been discussed before. I have gone through the threads multiple times and I just couldn't find it.
So for the 2017 GLE-350 4MATIC M276.955 engine (non-AMG), what are the torque specs for the idler pulleys? From document AR13.20-P-0001GQ, I have:
1) Screw/bolt, poly-V belt tensioning device to timing case cover, 20 Nm. I believe that this is the two bolts holding the tensioner;
2) Screw/bolt, guide pulley to carrier, 25 Nm. I assume that this is the one to the right when facing the car;
3) Screw/bolt, guide pulley to coolant pump, 35 Nm. I assume that this is the one next to water pump pulley, to the left when facing the car.
My confusion comes from the fact that the two idler pulleys are identical, but one has a higher torque of 35 Nm. Is that correct?
I have also read, on some Mercedes, the first installation is 35 Nm, presumable the screw/bolt needs to tap a thread into an untapped aluminum frame; and following installation is 25 Nm.
Thanks to everyone for the knowledge and enthusiasm. Mercedes is a fun car to drive, but definitely not an easy car to work on.
Thanks Chassis! Actually I got the document from your post.
So this is my interpretation, please see if correct.
I am nervous on this, because I have had tensioner bolts broken before (on Honda). After the Dealership fixed my work, the bolt broke as well after a few months. And they did it again under repair warranty, and it has stayed put so far.
So apparently some parts have a very narrow margin of error.
I decided to go down this rabbit hole a bit further. Assuming that the drawing from MB is true to proportion / scale (the pulleys still look round to me), we can measure the angle of the belt routing.
The idler pulley #2 will subject to ~20% more lateral force than #3, which translates 25 Nm to 30 Nm. So it is in the right direction.
As to how lateral force translates to bolt pre-load, especially when pulley bearing sits in a small "pedestal" *boss* of half depth, I have to look.
Last edited by Seiko; Mar 1, 2026 at 04:27 PM.
Reason: Use correct terms.
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