I would have to agree with Dan, that belt would have to stretch a lot, there is very little stretch available in that type of belt. Other option is deflection of the structural components, but I don't think the forces are great enough to cause that. We could do some simple torque calculations to estimate the forces involved.
Inge, stretch in a Harley belt is call a break...
These belts do not stretch, they are literally as tough as chains, hence the Gates name of Polychain for their belts.
Harley uses Gates belts, but they are made to a slightly different level as retail available belts. Other manufacturers such as Falcon make replacement belts for Harleys. In the case for Falcon on the newer touring Harleys at a pitch length of 139, they don't stretch, they just break after a couple thousand miles.
The way the rear swingarm is made and the BB mounting, I don't see anything there that's going to bend under load enough to cause any issues.
I'm not sure how much compression the older Harley compensator system has, but the one I have at home shows extreme wear on the crowns for the three ramps. IF one was worn enough, I could see it jumping ramps, but it would probably sound more like a machine gun going off for a few quick shots. I don't see it just jumping one third rotation and stopping without hitting several before stopping. This is IF it has enough wear to allow this to happen.
I'm sure that some here have the Centa comp and still gets this "jump" sensation too.
Back to the belts, break not stretch.
