M103 serpentine belt change procedure needed
 

Hello: I need to change the serpentine belt on my 1990 300SE vwith the M103 engine. I just want to change the belt right now, not the tensioner...

The Mercedes M103 Engine Service manual states a procedure whereby the tensioner bolt and the tensioner adjusting rod are slackened. However, it goes on to state that "from November 1986 the alternator is attached at the bottom bracket with a 13mm collar bolt. If this collar belt is removed the V-belt can be slackened by swiveling the alternator without slackening the bolt." The bolt they're referring to is the tensioner bolt.

So, I'd like to know if anyone has changed the serpentine belt on a post '86 and pre '92 M103 by just removing the collar bolt on the alternator in order to slacken the belt.

Thank you.

For proper re-tensioning of a new belt you will need to follow the usual procedure. This is a good shorctut if you are using the same belt.

Remove the fan shroud, loosen (but don't remove) the 19mm bolt that goes through the tensioner assembly. Then loosen the 13mm adjusting bolt tower near the water pump until belt is detensioned. The adjusting tower is reverse thread, but left is still loose, right is tight. After you fit the new belt, tighten the 13mm adjusting nut until the belt is at proper tension (as noted by the position of the clear plastic arrow on the tensioner body). Tighten the 19mm after tension is set ONLY. Very simple.

Thanks for your help. I appreciate it.

By the way, the manual states that the fan clutch needs to be removed. However, a fellow member advised that the clutch does not need to be removed unless I'm also changing the tensioner. That seems to be correct as you didn't mention removing the clutch either.

If you have small hands you can usually get away without removing the fan clutch. Getting the new belt into place can be kind of a pain, but its certainly doable.

Thanks again. I'll give it a try tomorrow.

The tensioner bolt that you have to loosen first is in between the power steering pump pully and water pump pulley. Its hard to see even with the fan removed (It's bolt #16 on the diagram). It won't feel like it's loosening for a number of turns but keep doing it until you feel less resistance. Then do the tensioner 13mm (#5) brass adjustment counter clockwise. You should feel the belt start to loosen at that point. You can use the diagram as a reference to reinstall the new belt :cool: