jej3

All -

I am away from my WSM but wanted to know what the proper AC belt tensioning procedure is....

I'm starting to think I've been a bit stupid about this but here's what I did and I think I might have gone about it backwards

1. Loosen 17mm pivot bolts on top front/back of compressor
2. Loosen the nuts on the adjusting bolt
3. Leveraged the compressor away from the enging with a wood handle between compressor bracket and oil pan and tightened 17mm rear and front bolts while maintaining tension
4. Tighten locking nuts on adjusting bolt

Continue to get squealing/slipping belt periodically Definitely belt squeal because when I hit it with WD40 or "Belt Conditioner" it stops.


I am starting to think that I should be using the adjusting bolt to tension the belt and then lock down the pivot bolts on top front/rear.

Going a bit mad every time the belt squeals so your input is appreciated.

dprantl

There is a nut on the adjusting bracket that as you tighten should rotate the compressor away from the engine and tighten the belt.

Dan
'91 928GT S/C 475hp/460lb.ft

nc_growler

Is there any possibility that this is due to A/C compressor clutch engagement issue?

Tom in Austin

Yes, you should be using the adjusting bolt to tension the belt and then lock down the pivot bolts on top front/rear. Correct tension is when you can just depress the belt 20 mm with your thumb at mid-point.

jej3

I wouldn't say unequivocally no to this being a compressor clutch issue but I do know if the belt isn't slipping, there is no noise and only the load of the compressor causes slipping.

The optimistic side says I just need to tighten this belt the right way, I think. If that doesn't get it then I'm going to go find a 12.5 x 1080 belt vs. the 13 x 1080 that replaced the erroneous 13 x 1125 that I was provided when I did my TB/WP.

Mountains of non-928 stuff to do before SITM so I hope the adjusting procedure finishes this one off.

Thanks to all for the input

dprantl

You meant 13x1075 or 13x1070, not 12.5x1080, right?

Dan
'91 928GT S/C 475hp/460lb.ft

jej3

Well, 928intl sells a 12.5x1080 belt, 928srUs provided me with a 13x1125 belt and I am not sure what 928Specialists provides for 1990 MY but they do have the P/N from 928intl.

My local autoparts store correctly identified the length as 1080 but they had a 13 (which is what I thought I needed)

Having the wrong width belt seems to be an issue that is rarely experienced. But was experienced here

I'm hoping to end the hardest part of my TB/WP change.... making this F%&^*ng squeal go away. Of course it is only 96F today

jej3

I guess I'll be ponying up for quite a bit more than I bargained for. During a spirited drive home tonight, my belt decided it didn't want to be on the car anymore. Thankfully it is the only thing gone!

Now it's time for another post....

dprantl

12.5x1080mm is the stock belt for '90+ 928's with the 10PA20C compressor. However, for some reason that length on my car would require maxing out the adjuster completely to get tight, and even then it wasn't that tight. So, I went and got a 1070mm, but it was too short. I could have forced it on, but then I found this instead:

http://www.performanceproducts4benz....12-5x1075.html

Fits great and I can get it nice and tight.

Dan
'91 928GT S/C 475hp/460lb.ft

jej3

Thank you! I'll see if I can source it locally before I start all of this nonsense again

Bill Ball

You may bebe missing part of the tension adjuster for the belt and you probably aren't getting it snug enough just by leveraging the compressor and then tightening the bolts. There should be 13 mm nut on a threaded rod on the adjuster arm that can be cranked down to get proper tension. V-belts don't have to be terribly tight, but I think it's 10mm with thumb pressure. See bottom arrows in the pic below for adjuster.

jej3

Thanks, Bill. All parts are there and accounted for, except the one between my ears