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Old 05-Nov-2004, 01:03 PM
chris_of_1979 chris_of_1979 is offline
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Belt change...

I've heard it talked about before by many people, but is it seriously viable to change the cambelts properly without using the tensioning tool?

As mentioned, I've heard that this is possible from several people - including a couple of people who service Duke's for a living (mentioning no names) who reckon the tool is a waste of time.

How viable would it be for someone who is changing belts for their first time though?!?!?!

Also - if there's anyone within a couple of hours of me that might be able to show me exactly what I'm doing - that'd be rewarded with several beer tokens and a stack of favours as needed.
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Old 05-Nov-2004, 02:21 PM
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Fordie Fordie is offline
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Chris, Some people are happy doing them, some ai'nt. I for one would rather pay the price of about £100/120 knowing that the jobs been done right and I can ride the bike without worrying . On Ye Bike done mine locally. 4D
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Old 05-Nov-2004, 02:36 PM
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ali ali is offline
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Changed mine with the help of Rich at Louigi Moto last spring. Very easy on the SL as there's no outer lip on the drive sprocket/cog, so they slip straight off. He did the tension by hand and I've kept an eye on it all season. I've read several reports lately from race mechanics recommending that you run them very loose if you're revving the bike out, so I haven't been too stressed about an extra mm of play.

Since replacing I've done 6,500 miles, including 5 TDs, with no probs. Now going in for top-end service and I'll get them replaced then.

No idea if the 4v is more sensitive to belt tension, but I'm sure someone (Nelly) can give you the full details.

Cheers,

Ali
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Old 05-Nov-2004, 02:39 PM
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DSC Region Organiser skidlids skidlids is offline
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I have the Snap-on tool and do my own belts, the road bike gets them changed once every 12 to 14 months, they were done last Sunday aftr the Moto GP. On the race bike it depends on the amount of racing, so only once this year but twice last year.
I did Wheelies for him earlier this year ( I see he has decamped from his Summer home by the river to his winter location just down the road from my works).
Chris I maybe able to make it up to your place sometime with the tool and some guidance, when do you need to have them done.

Kev
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Old 05-Nov-2004, 03:15 PM
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DSC Member Shazaam! Shazaam! is offline
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First of all, it's critical that the cam belts be replaced every 12,000 miles. Space limitations on motorcycles require the use of smaller diameter pulleys that cause the belt to flex more than large pulleys used in automobile engines. Further, Ducati uses a small diameter back-side belt-tensioning idler pulley arrangement that causes the belt to flex in the opposite direction on each revolution. This design approach results in an even greater angle of belt flexing requiring the use of a stronger reinforcement fiber to prevent fatigue failure. The original drive belt design often failed before the first 12,000 mile replacement interval so Ducati switched to a Kevlar fiber reinforced belt.

Itís also important to inspect the idler pulley bearings at each change and also a good idea to replace the belt tensioner locknuts.

Second, Ducati tells us that the proper belt tension is critical to avoid over-tensioning the belts that can lead to premature failure. No one argues with this.

I think itís interesting to note that the Ducati tool for checking the belt tension on the 4V motors has changed for the testastretta. The testastretta engines, as well as all new dual spark engines, use a harmonic tester that can only be used with the Mathesis diagnostic tool. Also, Ducati now specifies different tension specs for the vertical and horizontal cylinders.

The main reason for tensioning in the first place is to prevent the drive belt from jumping a tooth or walking off itís pulleys. I would think that the minimum tension to prevent this is well below Ducatís specs. So why are they so picky about it?

My guess, for what its worth, is that they canít control the manufacturing specs close enough on their supplierís belts. The suppliers are able to supply belts with adequate tensile strength and at the dimensional tolerances needed, but thereís probably a significant variation between suppliers and production lots regarding belt stiffness.

So you just stretch a less-stiff belt a little more to get the proper tension, you say? Well, yes and no. In terms of linear stiffness, yes - it makes little difference. But in terms of bending stiffness, it changes the way the belt vibrates between pulleys, and in particular, the frequency that it vibrates at. It certainly changes the natural frequency of the belt so as to resonate at different engine rpm. The different specs for the horizontal and vertical cylinder belts is the clue here.

So what? I think that Ducati has traced belt fatigue failures to this phenomena, so theyíre trying to control the belts harmonic vibrations instead of just tension.

Of course, itís still possible to cause belt failure by overtensioning it.

One point bears mentioning here. Thereís been a lot written about how to accurately set belt tension. No matter what method you use, what's critically important with any toothed belt is the need to rotate the crankshaft (and the belt) after you set the tension, to assure that the specified tension is the same everywhere along the belt, not just in the part of the belt where you first placed the tension gauge.

If you service Ducati 4V motors for a living, you have set the tension in the belts enough times using the required tension tool and procedure to have become pretty well calibrated yourself as to how tight is tight. So an experienced technician may indeed feel itís a waste of time. They remember how much the belt will deflect between pulleys when under maximum tension when the engine is hot - and how the same belt feels when everything is cooled down. In other words, they have a ďfeelĒ for the spec when they double-check using their calibrated push and pull on the belt.

The rest of us need the tool.
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Old 05-Nov-2004, 03:41 PM
desmojen desmojen is offline
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Skidlids, how much was your snap on tool? Plus, do you have a cat number for it?
I would like a belt tool but don't fancy paying for the ducati one!
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Old 05-Nov-2004, 03:42 PM
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Derek Derek is offline
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Quote:
No idea if the 4v is more sensitive to belt tension
This is something I'd like to find out more about. I've changed the belts 3 times on my SS and a couple of times on friends's SSs and I'm about to do my own again. I've also done a few car cambelts with no subsequent problems. For next year I'm intending to move to an ST4 and want to continue doing my own servicing and don't really want to have to take it to a dealer to get the belt tension checked.
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Old 05-Nov-2004, 04:52 PM
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deej deej is offline
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sounds too complicted for me mines off to my local dealer to get the belts done.
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Old 05-Nov-2004, 07:16 PM
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weeveetwin weeveetwin is offline
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I changed mine on my 888 for the first time last year, using info I found on various web sites to guide me. I've no belt-tensioner tool, but found it to be a simple enough job. It took about three hours from start to finish. (The biggest shock was discovering just how slack the old belts had been!)
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Old 06-Nov-2004, 01:32 AM
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I use the factory tool for the 4V's engines and the old fashioned way of tensioning by feel and a 5mm allen key on the 2V's.
I always run the rear cylinder a little tighter than the front one to, not much though, to allow for th etemp. differences.

I'd agree with Fordie though, if you're in any doubt is the risk really worth it?? £65 for the belts and an hour or so labour and that's it. You get one snap and it's a whole different world of pain than saving £30.........
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