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Belts And Valve Shimming

Discussion in 'Technical Help' started by Harris911, Dec 11, 2019.

  1. My recent to me 900ss is undergoing a minor overhaul to return it to the road so I have been having a go at checking valve clearances and changing the belts. I have had a few issues and wondered about previous levels of maintenance. The belt on the vertical cylinder was almost broken (see picture) and the first valve I checked (inlet vertical) was at 0.005 on the opener the closer was free and less than 0.003. The difficulty I had was sliding the rocker over when the clip was off needed me to rotate the cam and slightly depress the valve to get it to slide over, also when I loosened the belt tensioner I really struggled to get the belts off, they were original Ducati belts and the horizontal belt was in good condition. Could the cam timing have slipped? Could it have the wrong belts fitted? Would the tight valve have caused the belt damage? I had the bike running before I started stripping it and it ran ok.

    DD4BA362-2930-47E6-9D54-9597CA4033C8.jpeg
     
  2. Getting the belts off the easy way without cutting them.......

    See below.....when the adjuster is slackened off, the belt will be loose; so pull the belt outwards and flip the adjuster from the outside of the belt so it is on the inside of the belt.



    7) BACK AND FRONT.jpg
     
  3.  
  4. I took the adjuster off completely still struggled to get the belts off?
     
  5. If it ran OK before, then it seems unlikely that anything had slipped, or that the belts were the wrong length. However, I'd now be very careful as to what the positions of the cams and crankshaft are, and not turn anything over vigorously. I wonder whether it wasn't at TDC when you took a belt off.

    It's a while since I've done this job, but I did do some research as to where everything should be positioned beforehand, and put paint marks on old belts, pulleys and new belts, to make sure everything went back together in the same position. You could take a look at some Youtube videos on the topic and there's probably a good write up here at ducatiforum, somewhere. I did at one time file this link away, which shows a number of jobs being done on a 750SS, including belts: https://www.pistonheads.com/gassing/topic.asp?h=0&t=982468&d=0&nmt=
     
  6. That belt is not just nearly broken, it’s shiny instead of matt and all the lettering has worn off.
    Has the adjuster or idler pulley seized perhaps ??
     
  7. Certainly investigate the tensioner bearings but maybe the belt was too tight?

    The tight clearance wouldn't cause it, as long as the cam turns freely, and IMO the closers want to be as tight as you can get without drag.

    Lucky the belt didn't break and cause mayhem - My Son called me from the roadside a few months ago when his car just 'stopped' with what appeared to be a broken cambelt, I thought it odd that the belt was still tightly in place, closer inspection showed it to be like this around the crankshaft pulley;

    [​IMG]

    And all the exhaust valves were bent...
     
  8. Same as wot happened on my MR2, although that was a mixture of inlet, exhaust valves and two pistons.

    Non OEM belt (apparently) didn't like me going at 100mph.
     
  9. Fortunately the pistons were OK and I repaired it (Renault Clio).

    Son was happy as the total cost of the parts and required tools was £100 less than cambelt replacement that he didn't do when he should have (which is why it broke) so he reckons he'll just run it 'till it breaks again and then get me to fix it... :(
     
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  10. Tensioner bearings all spin freely, there was a bit of surface corrosion/muck which I cleaned off with scotchbrite. Main concern was how difficult it was to remove the belts and that was after I completely removed the tensioner. I am concerned about damaging new belts when I go to put them on
     
  11. Perhaps they were the wrong belts for your engine (too short by a smidgen). Any numbers on them to confirm?
     
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  12. Imho, something is definitely wrong.
    All the belts I’ve ever taken off my SS and 999 have been in excellent condition.
     
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  13. If they were Ducati belts ( maybe they're not) no others would fit. One tooth shorter wouldn't go on and one tooth longer couldn't be tensioned.
     
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  14. Any theories then, Derek ??
     
  15. If the belts (both) are very tight with the tensioners removed out of influence.
    #1 Either the belts are wrong, but this has been addressed.

    Or
    #2 The distance between the belt centres is wrong( too long).

    Has anyone had the barrels or heads off and are the gaskets standard ?
     
  16. Or is it the pulley edge retainers? Some people have had issues getting the belts over them.
     
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  17. Yes it could be. These haven't been mentioned yet. Ducati stopped fitting them about 1993/4. Every bike that I've worked on where these flanges were fitted I've pulled them off with a pair of pliers. They are completely unnecessary and a total hindrance.
     
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  18. Derek, that perhaps indicates that the 750 is fundamentally a completely a different engine to the 900; because mine had the flanges, but never had to remove them and the belts could be taken off easily.
     
  19. There are many differences between the 750 and 900 engines, not just the bore and stroke. The stroke being shorter means that the belts are also shorter but there may be a little more tolerance to allow the belts to be slipped easily over the flanges. On the 900 engines its a real bugger and fitting the new ones in even worse.
     
  20. Mine has flanges on the cam pulleys I do not think the engine has ever been apart it has only done 20000m and the belts were OEM Ducati ones so possibly only the second set?
     
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