Ducati.ms - The Ultimate Ducati Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter #1
My scrambler 2016 classic timing belt had broken. I was on high way but as soon as stopped, I pull aside my bike. After that, I changed timing belts and restart. It worked but as I pull the throttle, engine stop. Is there any possibility the engine damaged? I wish I had no damage...
 

·
Premium Member
Joined
·
796 Posts
The scrambler has an interference engine?
I think the old ducati bikes only have it..
I could be wrong but I don't think that there is a single Ducati built in the last 30 years that DOESN'T have an interference engine.
 

·
Premium Member
Joined
·
796 Posts
C989DB28-2011-4223-8D9A-550CDB5FD763.jpeg
 

·
Registered
Joined
·
373 Posts
The leading contributor to belt problems is looseness. If the belts are "a little too tight" they are probably about the correct tension. AND all belts, the ones we make and OEM, will have the cords unwind a little as the belt breaks in, which results in loosening the tension. That's why the racing engines have a short run in on new belts, which then get re-tensioned for a race.

When there is a problem at idle, sometimes it can be repaired by the machinist. Normally not so when there are revs involved. :cry:
 

·
Premium Member
Joined
·
1,845 Posts
The leading contributor to belt problems is looseness. If the belts are "a little too tight" they are probably about the correct tension. :cry:
Ok...wow. I use your belts and tension to spec when installed. I don't retension unless they are below 75 Hz at room temp. When I do retension, I do it to 95 Hz or so. Is that correct?
 

·
Registered
Joined
·
373 Posts
Ok...wow. I use your belts and tension to spec when installed. I don't retension unless they are below 75 Hz at room temp. When I do retension, I do it to 95 Hz or so. Is that correct?
I would always retention to 99.

Factory spec is 110 Hz ... ours at 99 Hz "pulls down" on the camshaft with the same force as the OEM belts at 110.

When talking with the belt-maker (BesTorq, the manufacturer-importer in NE) we had many discussions and his refrain always is "the tighter the better". Part of the discussion was the safety of running our belts on an engine with factory 110 Hz of tension. With 10% more force against the shafts there shouldn't be a problem. Also, when bets get real tight they start making a god-awful chirping sound because rather than rest into the sprocket groove, they skip as they settle in. Sounds like you're murdering the bearings but it's the belts -- so that's a great way to know when "too tight" happens...
 

·
Registered
Joined
·
776 Posts
Factory spec is 110 Hz ... ours at 99 Hz "pulls down" on the camshaft with the same force as the OEM belts at 110.
Part of the discussion was the safety of running our belts on an engine with factory 110 Hz of tension. With 10% more force against the shafts there shouldn't be a problem.
Wrong. Since the fundamental frequency is proportional to the square root of the tension, a 10% increase in the fundamental produces a 20% increase in tension.

 

·
Registered
Joined
·
2,701 Posts
My math is rusty, but I think the formula you are using is for the force on the free movement part of the belt, not the anchor points like the tensioner and the cam gear - which is what Chris was speaking to? Because that part of the belt is free to oscillate, I don't think this formula by itself describes the force on the rotating endpoints which effectively creates a large amplitude wave by being circular (closed circle). I think the angular momentum of the belt also affects the mass quantity being used as a variable also. I don't know what to do with the power pulses from the crank on the belt movement, but it definitely is not a steady state, you can see the effect at idle with my light McNichols flywheel.

Out of practice with the math, it used to be good and I broke lots of things improving my understanding.
 

·
Registered
Joined
·
373 Posts
Wrong. Since the fundamental frequency is proportional to the square root of the tension, a 10% increase in the fundamental produces a 20% increase in tension.

It was measured on a machine with a load cell. By a guy whose degree thesis was about belt tension. I'll go ahead and trust measured results from someone in the belt industry.
 

·
Registered
Joined
·
2,701 Posts
By load cell you mean a force measuring device on the axle spinning a cam gear? That sounds like the best way, less math too.
 
1 - 14 of 14 Posts
Top