Nice Sunday afternoon job I thought… Needed to change the belts on my track 749R as they had been on ~4 years (but only ~650 miles). Belts are CCW/Exactfit, installed by me. I have done belts on all my bikes (916 once, 749R twice, 1098R twice and M1100 twice - always using CCW) and apart from the 916, I used the Ducatidiag software to set the tension to ~100Hz. Never had a problem before…until I removed the covers on the 749 today. Basically - there’s loads of nasty black fibrous deposits all around the belt runs. Appears worse on the vertical cylinder but has spread all around both vertical and horizontal areas. The tensioner and idler pulleys turn but have only tried with the belts still installed. See pictures below - note that I haven’t set the timing marks, this is exactly as they stopped after my last trackday in September, when it was running just fine. Vertical run: Inside of vertical cover: Horizontal run: I have yet to turn the engine over to look for anything that may have been rubbing on the belts or any obstructions. Thoughts are possible sticky idler/tensioner bearings but other than that, can’t really think what has caused this. Any ideas people?
That's interesting. The teeth on the belt look to be in great shape, the weave of the material is still clearly visible and both the peaks and troughs look like new. But from the images there looks to be some wear/scuffing to the side of the belt, which could be where the material has come from. It would be really interesting to see if the rear side face is also scuffed. It's also noticeable that the belts are hanging out past the edge of the pulleys with no guides fitted, which I don't remember seeing on any sets of belts I've changed. .
The edges of the belts are overhanging the edge of the pulley as if they have wandered outwards off the pulley a little. If they have, the guides on the pulleys fitted with them might be wearing the edge and producing the dust.
Agreed, in addition I thought the marking on the back of the belt (smooth side) looks excessive for the distance travelled. How does the tension feel between your fingers in the static position?
Tension feels fine but I haven’t measured it. I plan to remeasure them before I take them off, just to see what the value is.
I’m not familiar with that exact engine. But does the mesh on the inside of the vertical cover pictured look like it has rub marks on it from the side of the belt?
Good spot - the mesh for the vertical cover cooling vent does look out of place so it may indeed have been rubbing on the belt. I will investigate at the weekend as I felt the deposits were more pronounced on the vertical run. Thanks.
Brilliant ! All of the gauze is covered in debris, apart from those 2 shiny, polished areas, where the belt has been rubbing. It’s great to see problems like this being solved, hopefully
We’ll see - perhaps the mesh got displaced when I put the cover on (vertical cover is a bit of a pig to fit) and got caught on the belt - I will check but it does appear possible. Ta.
Little update. Couldn’t wait til weekend so rushed into the garage after work to investigate the mesh/belt interference potential. Found some ‘White Tack’ (white blue tack…who knew?) and stuck a big lump in the area of the vent/mesh on the cover then installed the cover. Spoiler alert - there’s no interference evident! The gap between the vent/mesh and anything nearby is quite generous, got to be at least 4mm difference in the vertical planes before anything would touch. The only thing I managed to get an impression of was the inlet pulley nut, circled below, and that was not near enough to the vent to interfere. Thick lump 5mm ish in area of vent - no impressions of anything touching: Very thick lumps, 8 to 10mm thick. Nothing touching. So, nothing conclusive basically. I plan to measure the tension at the weekend as it is suggested that the belts may have been slightly tight.
I think you are overthinking this mate. It’s a track bike with four year old belts. Just wack the new ones on and let her rip.
Shame, it looked like it could have been the mesh. Having said that, looking at your recent pictures you can see the mesh areas that looked polished in the original picture are showing a 2 part type adhesive. Did we mistake this for the so called polished areas of mesh?
Had similar on my Monster a few years back, horizontal belt only, was due to worn tensioner bearings. Replaced them all back then and recently (5 years later) just changed the belts again and no more dust/deposit. That said, the tensioners on the old air cooled 2v are not like the 4v as they are just bearings rather than pulleys with retaining lips so are more likely to run off if the bearings are loose, furthermore the bearings that were worn are actually just 2 roller bearings fitted side by side rather than the long 'special' bearing on the other pulley. Worth checking/changing your pulley bearings though.
