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Belt Tensioners

Discussion in 'Supersport (1974-2007)' started by Desmoquattro, Jul 10, 2017.

  1. Been spannering on my carby 900 SS today. Slightly concerned about the belt tension. Seemed on the loose side when I took them off and the adjustment on the tensioner is at full when I get my 90 degree bend in them once reinstalled. I'm running without base gaskets but apart from that I can't understand why there's no more adjustment. Belts were new on start of last year and its done less than 1000 miles in that time. Any ideas or suggestions?
     
  2. Wrong belts?
     
  3. That did cross my mind Derek. However part number looks correct.

    14997126145661602772594.jpg
     
  4. Yes, these are the correct belts for a carbed 900. Also for the 900SSie, M900, ST2 and 907ie. The 1000DS engine uses a different belt.
     
  5. Worn tensioner bearings? Too much finger pressure when trying to twist them through 90 degrees?
     
  6. The tensioner bearings are new on the adjustable side. When I twist it, I got to 90 but there's no room for adjustment should I need later on.

    Is there only one way the adjuster can be fitted?
     
  7. As you are tensioning used belts they are not tensioned as tight as new belts. I don't know how tight yours should be but perhaps try the sonic method of tension.
    Steve
     
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  8. Sorry, just checked my Haynes for the SS and it's very different to the 999 I have now, so ignore the turning in the wrong direction bit.
     
  9. Haynes says 45 degrees for new, so maybe 90 for used is ok
     
  10. Are you turning the tensioner the correct way?

    Here's an example of a badly set adjuster on a 4V engine.... it's been turned the wrong way to adjust tension. Although you get the same result, it forces the belts dangerously close together!

    bad_adjusters.jpg
     
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  11. I'm wondering whether I have perhaps set it up wrong. Gonna have a look at it tonight.
     
  12. I thought the same, as I have a 999 now but on checking my Haynes manual for the SS, the arrangement is very different and there is no eccentric adjuster which can be turned the wrong way. The adjuster moves in a curved track and is merely tightened in place once the tension is set.
    I guess the combination of used belts and the missing base gasket just mean you run out of adjustment.
     
  13. What make are these belts?
    Exige's belts allegedly stretch less than oem, so may be more suitable given the missing base gasket. Not that that should make a vast difference you'd think.
     
  14. Someone made/sold oversize rollers for use with skimmed heads.BBB Fabrications(Steve Bailey) maybe.
     
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  15. D'Oh! Of course! <slaps forehead>

    Is there any reason, apart from the cost, that you don't want to put new belts on?
    I would be worried using belts that are that stretched that you're getting to adjustment limits, even with a skimmed/no gasket setup...
     
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  16. I have another set of belts but as they have done less than 1000 miles and are expensive didn't want to put them on yet. I may go the cheaper route of putting larger bearings on the adjuster. Much cheaper alternative
     
  17. Is it not worth fitting them to see if they are any better?

    I would have thought that the cost of a new pair of belts (roughly £100 for my 2v Hyper) pales into comparison to the damage done when it throws a valve...
     
  18. There has to be some misunderstanding or something wrong here other than stretched belts.

    On both my M900 and 900SS if I'd used up all the adjustment on the moveable pulley the belts would be almost touching in the middle.

    Nasher
     
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  19. As said earlier .. twisting them by 90 deg to check/set the tension is incorrect .. it should be 45 deg.
    But I wouldn't use that method alone for tensioning anyway, in fact I would probably not use it at all .. the allen key method or frequency method are both more accurate.
    Have you studied Chris Kelly's video guide ?


    Also, I don't think there would be any difference between the tension required for old belts compared to new ones.
    These things are specifically designed to have minimal stretch and there's no way that a used one would require a different set-up to a new one.
     
  20. Ducati specify 110 Hz for new belts but 90 Hz for used ones on the 4v engines. There similarly differing figures for the 2v tasstengines but I can't remember them off the top of my head. So there must be some changes between new and old belts but I agree it will not be by much. There may be some initial stretch but as the belts get more miles the change in tension is probably more down to wear on the teeth.
    Frequency is the most accurate way to tension. Twisting it or pushing against it is subjective and everyone will have a different feel for what they think is right. I think the OPs problem may be more to do with his measuring technique.
     
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