My Belt tensioner recently destroyed itself. It actually came completely apart and the pulley ended up in pulley never never land. I purchased a new belt tensioner on-line and installed it yesterday. I checked the serpentine belt and it was in fine shape so I planned on reusing it. The new tensioner had the pin installed when it arrived so I assumed, install the tensioner, install the belt, release the tensioner pin and we'll be in business. The reality: I installed the new tensioner, and attempted to install the belt but it was too short. I checked and rechecked the routing of the belt and how it was seated on the pulleys and all is fine, but it just doesn't fit. I have just learned there have been modifications to the belt tensioner and the pictures indicate the old tensioner pulley to be smaller than the new replacement. Does this mean a new and different belt? I talked to the local dealership and while they tried to be helpful they were as confused as I am. Any help/advice would be greatly appreciated.


Hi Jim,

Sorry to hear about you problem withe the tensioner. This is a common problem with the M113 engine. I would recommend that you replace the serpentine belt as well.

I would check the routing of the belt. In the past when I replace the serpentine belt, it takes me two minutes to take it off, then about 5 trying to route the new belt.

Make sure that the belt goes over the water pump and to the tensioner. Then warp around the crankshaft pulley.

If you still can not install it, my guess would be that tensioner pulley is not the right size. 2000 e430 engine

Thanks for getting back to me so quickly. I know there have been at least 3 generations of the tensioner and I think at least 2 different size pulleys have been utilized. I was just trying to find out if a new belt will solve the problem. I spoke with Mercedes dealership and they were sympathetic but if I wasn't going to buy a $70,000 car......crickets!!! LOL

Technically yes, a slighlty longer belt will solve the problem. You will have to measure how much more length you need. Then you can go to Advance auto parts or autozone and ask for a new belt based on the total length that you need.

Ideally I would not go that route. If you do decide to go that route, make sure you either buy a spare belt and throw it in the trunk or wire the new belt size on the owners manual.

Something else you can do is get the part number from the old tensioer. You can do that by calling the dealer and providing the vin.

Then compare the tensioner that you have with the one you are supposed to have. Look up some pictures online.

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