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Discussion Starter #1
Here is just what the doctor ordered..... another cam belt thread.

Ever since I bought my first belt Ducati twenty years ago, I've been using the 5mm and 6mm Allen key method; it works and although not very scientific, is a simple method. However, I've always been puzzled as to why the front belt seems looser than the rear, even though the 5mm Allen should make it tighter. A 6mm will not go between the idler bearing and the belt, so the clearance is tighter, but it doesn't seem so. Looking at the belt layout, the position of the idler and tensioner appears slightly different between the cylinders, which may explain the discrepancy.

Idly skimming through the W M last night, I see that Ducati recommends checking the slack at the bottom run of the front belt and the back run of the rear belt......Interesting, as the Allen method involves checking at the top run of the front and the back run of the rear. So, today I downloaded the Gates app to my tablet and attempted to set the tension.

First observation is how difficult it is. The tablet has to be held still without touching anything and extremely close to the belt. Any external noise stops the app from working. At first the readings were all over the place, but gradually I managed to get some consistency and some interesting results: The rear cylinder (set with a 6mm Allen) gave an average reading of 98, the front (set with a 5mm Allen) gave an average of 85. After re-tensioning, I managed to get an average reading on the front belt of 97, and left it at that. As they are almost new belts, I know that the figure should be around 112 hz, but I prefer to err on the slack side.

It IS a difficult job to get right, requiring patience; and both my thumbs are red and sore from flicking belts. I reckon that a microphone would make the job easier, if a way could be found to fix it in place, close to the belt. The run where the reading has to be taken (bottom, between the tensioner and bottom pulley and back between idler and bottom pulley) is probably the hardest to access, but gives different readings to other belt runs.
 

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Cheap clip on USB mic makes it a hands free job. Pluck with either thumb to avoid blisters...

Direct quote from the LT Snyder bible:

"I checked the tension with a harmonic tensioner against that set by a 4mm allen key. The 4mm allen key method was around 100Hz on the rear/vertical cylinder but not the front/horizontal cylinder... I use the 4mm allen key method on all my dual spark motors ON THE VERTICAL CYLINDER ONLY. On the horizontal cylinder, the tension is much tighter because the pulleys are in different spots compared to the vertical cylinder - if you use a 1mm feeler gauge, you'll be in the ballpark, but to be precise you need to use the harmonic tensioner."

Pretty sure he knows considerably more about Duc motors than the majority of us here on Ducati.ms, so I decided to use a mic and app to set my belts instead of the allen key method. It really isn't that much harder than using an allen key unless you are trying to get EXACTLY 100Hz... and anywhere between 90 and 110 is close enough to be safe and very easy to accomplish with a repeatable result.

YMMV.
 

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Discussion Starter #3
I've just come back from a ride and the engine definitely runs better now, with better pick-up after gear changes and smoother running low down. Hardly surprising as the front belt had been slacker than the rear before, so the timing was out.
 
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