Now I have become confident of using belt tensioning software in preparation for changing my timing belts on my 749s I have measured the frequency of my existing Horizontal and vertical belts, which have now done 12,000 miles to be 65Hz. I appreciate that the specification when fitting new belts is 110Hz, and that they will inevitably loosen and consequently there will be a drop in frequency, but is 65Hz a tad loose? What would one expect so see?
As you say, the belts will stretch in service especially as they reach end of life. A combination of methods works best for me rather than 1 in isolation. How does the tension appear with conventional techniques ie Allen key / 45 deg twist / idler bearing slippage inside belt methods? I would expect all to be a touch on the looser side but perhaps not enough to require adjustment.
I was under the impression that the sonic method was the recommended one, I didn't think the Allen key method was possible as the internal curve of the casting makes this non -viable. As far as the 45 deg twist goes they feel pretty spot on, I was unaware of the ' idler bearing slippage inside belt' method!
Yes, other tests being more or less OK was what I suspected. Sorry didn't realise you couldn't use allen keys with that engine. FWIW, I have used the idler bearing slippage test on Italian sports cars for many years to ensure the belt tension is not over tight. Method is to take up slack by depressing belt in region of idler and then checking the idler rotates inside the belt. If its too tight, belt friction will prevent bearing slippage. Like most things, once you are used to the feel you can also sense if its correct or too loose. Even if you are not used to this method, it can still be used as a simple check for over tightness although that appears to be the reverse of your case. hope this helps
Nigelo Now you have described the idler bearing slippage I can understand it. I have just tried mine ( old existing belts in place) and I can turn both idler pulleys comfortably with my fingers the belts are rubbing on the belt but not so much that the friction is preventing rotation. Thanks for that, much appreciated.
Which program are you using. i've just checked my belts today , one was 90 the other 75 , happy with the 95 so put the front cyl to the same. By the way I used my laptop program and tried it alongside an iphone app recommended ( a gates one) by someone on here, but I couldn't get on with it.
Peter I'm using the one called 'Tension des courroies' mainly because it was A) recommended by someone on here, and B) I had problems downloading others, and c) it's free! Once you get the hang of it I find it very easy to use, and with the cheap clip on microphone that clips conveniently exactly where you need it to be on the 'casting lip' confidence inspiring, as with a little practice easy to get consistent repeatability of the readings. Let me know if you want links for the microphone .99p from e bay , delivered, and software link. I didn't use a smartphone because I don't have one, and could foresee problems getting the phone in amongst the gubbins on the vertical cylinder!
I'm fine for the microphone thanks and the program I'm using is pretty good (visual analyser 2011) although a little confusing until you're used to it. i'm up for trying an easier less complicated one though so I'll download yours in comparison thanks Pete .
Peter The beauty of the programme I mentioned is that there is a clear vertical yellow line with the 'target frequency' in the middle of the screen, so all you have to do is to tension the belts so as the the Red vertical line superimposes on top of the yellow. btw each square of the graph represents 15Hz
A little late but I always re tension mine to 90Hz . Last time , after 1500 miles they were at about 87. So they were left alone.
Here's some advice I got from Skidlids over on DSC Ducati belts Fitting New - 110 Hz +/-5Hz Fitting Used - 90-100 Hz (+/- 5Hz) Testing already installed - above 70Hz You should not re-adjust the tension to the new belt spec max after run-in
It does appear that my 12,000 mile belts are just a little loose. I spent a while measuring them to ensure I was confident using the software. I will do an experiment, hopefully tomorrow, now I have the correct sized ring spanner, and see if I can manage to tighten them to 90-100 Hz=/-5Hz Once I am happy I can do that I will remove them and put on the new. Thanks for that, much appreciated.
