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Discussion Starter · #1 ·
My 05 ST3 has lived something of a garage queen existence. I'm its 3rd owner having bought it 18 months ago with 3200 miles on it. For circumstances beyond my control it sits today having accumulated only 4500 miles. Today I embarked on my first attempt on cam belt replacement, having read what I can find on this forum and in LT's book. I have no idea if they've ever been replaced before but I kind of doubt it.

I'm a bit confused on the 5 mm tension method. Not yet having removed the old belts, they seem so tight that I can't get anything between the idler bearing and the belt and certainly not a 5 mm allen key. Yet they seem to meet the 45 degree twist rule. Maybe the horizontal belt is a bit looser the vertical is a bit tighter. But neither belt can I even get so much as a 1 mm feeler gage between the belt and idler.

So am I misunderstanding this somehow? Is it possible that someone replaced the belts and set the tension way too tight?

Any guidance would be kindly appreciated.
 

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Those sound like they are very over tightened. Not having done a 3V Duc, but having done belts many times on a 2V Duc, I can say you should be able to fit the 5MM key between the idler and the belt with just a bit of resistance. You're using it like you would a feeler gauge. The conventional wisdom there being the gap is set right when the drag feels about what it would feel like slipping the feeler into a large phone book, if that makes any sense!

Just to be clear, the measurement is taken between the back side of the belt and the surface of the roller.

The other gotcha is the cylinder being checked must be at TDC compression. When all the timing marks are lined up, the horizontal is at TDC compression. You need to rotate the engine for the vertical cylinder be at TDC. The reason is because the closer spring on the vertical will be loading the belt and giving an improper tension with the horizontal at TDC.

Maybe just skip the 5MM thing and try the sonic method. I resisted for years until this last time. Easy, accurate, repeatable. I downloaded a free guitar tuner app for my phone and just used that.
 

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My 05 ST3 has lived something of a garage queen existence. I'm its 3rd owner having bought it 18 months ago with 3200 miles on it. For circumstances beyond my control it sits today having accumulated only 4500 miles. Today I embarked on my first attempt on cam belt replacement, having read what I can find on this forum and in LT's book. I have no idea if they've ever been replaced before but I kind of doubt it.

I'm a bit confused on the 5 mm tension method. Not yet having removed the old belts, they seem so tight that I can't get anything between the idler bearing and the belt and certainly not a 5 mm allen key. Yet they seem to meet the 45 degree twist rule. Maybe the horizontal belt is a bit looser the vertical is a bit tighter. But neither belt can I even get so much as a 1 mm feeler gage between the belt and idler.

So am I misunderstanding this somehow? Is it possible that someone replaced the belts and set the tension way too tight?

Any guidance would be kindly appreciated.
I have never been comfortable using the allen key method used for 2 valvers. I use the 45* twist method instead and it seems to work fine for me. The 45* twist *is* subjective yes, but perhaps can be described as needing moderate increase in twisting force to get to 45*, and then a significant amount of twisting force to go to "47*" at the longest run on each cylinder.

Once I install/tension mine, I of course turn the engine over by hand several times to check for interference before I put heat to it. Once I start it I let it run until *fully warmed-up* rolling the throttle on and off occassionally as well, and listen for any noticable increase in pulley whine. If they start getting louder after the cylinder expands and tightens them up even more, the belts are too tight. The whining from the pulleys should remain constant, with no appreciable increase in whining IMO. YMMV. :)

I recommned buying some spare bolts for the pulleys as they have special heads that will shear to save the cylinder thread if torqued too much, and even as I found using less than the full torque, but from repeated re-use. YMMV. :)
 

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I know the '06 ST3 use the harmonic method of checking belt tightness. I think it's the same for all the years of manufacture (but I'm not sure). In that case, the 5mm allen wrench method won't work.
 

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Mr Leakered
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If you use the CA Cycleworks belts, they come marked with a tuning freq. Early on, Duc noted 110hz for all engines, but I think they changed that.

Have a good one.
 

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Discussion Starter · #8 ·
One man's experience.....

The CA Cycleworks belts are labeled with 99 Hz as the recommended tension, with 110 Hz as the max allowable. I ended up with mine at about 104 Hz, pushing up on the idler as hard as I could by hand. When I was done, the 45 degree test applied, the 5 mm key test not so much. In fact I could barely get a .010" feeler between the idler and the belt.

In case it helps others, I ended up using an $8 computer microphone hooked up to my laptop with a guitar tuning app called AP Tuner. It gives a readout in a particular note and according to the Wikipedia article, 104 Hz corresponds with G#2. I tried another app called Pitch Perfect with which I couldn't get any sort of reasonable, repeatable reading. I also tried what appeared to be a very nice app called Cleartune for my iPhone 4 but it seems that the duration of the pitch was too short for the microphone in the iPhone to pick up. Just another watchout, after I worked up a nice blister on my thumb from thumping on the belt again and again, I started wearing some gloves at which point the frequency readings went all over the place. It turns out that the microphone was picking up the sound of the leather glove hitting the engine case.

Chris at CA Cycleworks was also a big help. In addition to having a Youtube video on the subject, he also was kind enough to take the time to talk me off the ledge after I managed to remove the vertical belt without marking the layshaft end.

It's all back together now, seems to run fine.
 

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My 05 ST3 has lived something of a garage queen existence. I'm its 3rd owner having bought it 18 months ago with 3200 miles on it. For circumstances beyond my control it sits today having accumulated only 4500 miles. Today I embarked on my first attempt on cam belt replacement, having read what I can find on this forum and in LT's book. I have no idea if they've ever been replaced before but I kind of doubt it.

I'm a bit confused on the 5 mm tension method. Not yet having removed the old belts, they seem so tight that I can't get anything between the idler bearing and the belt and certainly not a 5 mm allen key. Yet they seem to meet the 45 degree twist rule. Maybe the horizontal belt is a bit looser the vertical is a bit tighter. But neither belt can I even get so much as a 1 mm feeler gage between the belt and idler.

So am I misunderstanding this somehow? Is it possible that someone replaced the belts and set the tension way too tight?

Any guidance would be kindly appreciated.
Feel free to give me a call.
 

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I know the '06 ST3 use the harmonic method of checking belt tightness. I think it's the same for all the years of manufacture (but I'm not sure). In that case, the 5mm allen wrench method won't work.
I have done belts on my 2 valves and my 3 valve bikes. On the 2 valves I did both by the 5 mm, 45 degree twist, and the harmonic method. I finally purchased the MotoReva tool & they are spot on all the time. On the 3 valve, you can't do the 5 mm key method. Chris Kelly has a great video that show you how to do the 3 valve belts. Brad Black has a great video on how to do the 2 valve belts. The Ducati manual states to set the belts at 140 Hz, but it is wrong. New belts should be at 110 Hz, rechecking the belts(used) should be at 99 Hz.
 
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