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1989 300SE 232k miles
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1,032 Posts
Discussion Starter #1
Hello All,

This regards my 1989 300SE with 233k miles. I replaced my belt tensioner system (tensioner pulley, tensioner adjustment rod, piston). I put all the pulleys back in place and am trying to install my new s-belt. But I can't get it on.

Initially, I installed it the same as the last person. But it was super-loose. So I looked up some diagrams and realized it wasn't in the correct pattern. However, when I try to install the belt in the proper pattern, it's super-tight. I can't get it even halfway around the last pulley, no matter which pulley I've made the last.

I adjusted the new tensioner all the way one direction. I adjusted it all the way the other direction (It's currently to the point where I have threads out the top of the nut). It doesn't seem to make much of a difference. I'm not sure how much travel there's supposed to be in the tensioner, but I need about another 2 inches. To which, I know the 19mm bolt is loose. But I'm wondering if the bolts for the piston play a roll. I made them pretty snug. Maybe they're a factor?

I've replaced a few belts on the m104 with the self-adjusting tensioner. I never had this issue with those.

I came home and read there's an actual order for installing the belt. I plan to try that tomorrow. And maybe a screwdriver to try and slide the belt onto the last pulley. Maybe I just need to muscle it?

Any suggestions?

Thank,
Bill
 

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'91 560SEC, '91 300SE (sold), '98 Yota, '02 S-10 Hauler
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8,929 Posts
IIRC I had to muscle the serp belt a little but had to make sure the adjuster screw was as loose as I could go. There is supposed to be a little plastic pointer on the tensioner so you'll know when you have it tight enought (but remember I sold my SE 6 years ago) I can't remember whether this shows loose or tight
Tesioner Closeup 002.jpg
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Registered
1989 300SE 232k miles
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1,032 Posts
Discussion Starter #4
Thanks guys. I went back to the car tonight. I did a couple things. I turned the 13mm adjustment bolt until the bolt itself was loose; it jiggled. I then followed the installation order on the appropriate diagram there. After I put the belt on the idler pulley (#9), I needed to use a screwdriver to slide the belt back over the AC pulley (#3/4), and over the power steering pulley (#10). I then lifted it straight up, by hand, to the left and right of the water pump pulley (#11). And that allowed me to place it on that last pulley (#11).

At this point, the tensioner was loose, so I tightened it down. I used my little plastic arrow gauge and my sense of touch to determine when it was tight.

The car started and ran perfect. In fact, I was 3/4 the way home when I realized I forgot to tighten the 19mm bolt on the tensioner. So, hopefully the bolt held and will be there in the morning, when the engine's cool

Thanks Everyone! This was an experience. And, I'll keep plugging along at restoring this thing.
 
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