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A/C tensioner / belt

Discussion in 'Technical Q&A' started by WaltP, Nov 17, 2003.

  1. WaltP

    WaltP Formula 3

    Nov 1, 2003
    1,458
    Cape Canaveral/Atlanta
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    Walt P
    I'm just finishing up some maintenance on my 1980 308GTSi and found something that I wanted to ask you all about. When I was removing my A/C belt and tensioner bearing I found that the tensioner pulley didn't have any pressure on the A/C belt. I thought that maybe the PO had the wrong belt on. When I installed the new belt the same was true, the belt was so tight that I didn't have to put any tension on is from the belt. Has anyone else seen this?
     
  2. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Steve Magnusson
    Yes, but in a little different form. On my ex-308-2V there were shims (maybe 8~10mm total thickness) added to decrease the crank-to-AC compressor distance to give more/some wrap on the AC idler pulley (but it's still a pretty marginal design IMO).
     
  3. WaltP

    WaltP Formula 3

    Nov 1, 2003
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    I was aware to be on the look out for the shims but I had none. I'm seriously thinking about leaving the tensioner bearing and assembly off the car when I put it back together, it isn't too hard to get back in there if I later decide to put it on. Can you or anyone think of any down side in doing this?
     
  4. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
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    Philip
    I've just been through this. I had two shims on each of the upper posts of the AC compressor and the belt was too tight. Not quite guitar string, but definitely too musical. I had a couple of shims made and the AC comp cam down just enough for the tensioner to take up a small amount of slack. If it is too tight, you'll kill the compressor bearings. The tension specs are in the WSM for new and used belts.
     
  5. Steve Magnusson

    Steve Magnusson F1 World Champ
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    The downside is that without the idler pulley in place you'll increase the unsupported distance on the slack side of the belt, so depending on the runouts of the crank pulley and AC compressor pulley, the slack side could oscillate pretty wildly at certain RPMs (if the resonant frequency of the vibration for the extra length span is in band).
    The SPCs actually show the nominal condition as "2 shims present" on each stud, and I wouldn't consider a missing AC idler pulley as a "plus" so why not add the shims and adjust as per design? IIRC the max shim amount gets limited by the stud length and keeping enough thread for the nuts on the top -- and I'd add the max shims to increase the wrap angle on the idler pulley -- JMOs.
     
  6. CraigFL

    CraigFL Formula Junior

    Jan 17, 2001
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    Craig
    I'm not sure about the 308 but my 328 is a Euro and the A/C belt is different. I'm sure that I could put a US belt on but it would be too tight. The Euro belt is slightly longer and a much better fit.
     
  7. WaltP

    WaltP Formula 3

    Nov 1, 2003
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    Walt P
    I'm starting to like the idea of using the tensioner pulley now. With no shims to put back in or use as a guide, how much should I drop the A/C compressor? Those of you that have shims, what is their thickness?
     
  8. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Walt -- Measure how far the threaded studs protrude above the 3 nuts on the top of the upper bracket (hanging off the camcover) -- that will be the "easy" max total shim size you can add. The "stock" shim is shown with a slit (like a camber adjustment shim), but thick washers would work OK too IMO.
     
  9. WaltP

    WaltP Formula 3

    Nov 1, 2003
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    Thanks Steve, I'll do that tonight.
     
  10. WaltP

    WaltP Formula 3

    Nov 1, 2003
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    Walt P
    2 washers between each bolt and the compressor did the trick. Thanks to all!
     

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