GEBE belt breakage (picture)
In my case, the belt broke on the tooth side of the belt while the belt backing stayed intact. I stopped the engine as soon as I detected massive slippage. If I ran the engine longer, the belt backing might have broke as well. In the picture, I bent the belt backwards for better visibility.
From the picture, one can see the frayed fibers. Inspecting the rest of the belt, there are a couple of other places on the belt where fiber fraying has started on the belt edges. The peak of one belt tooth looks like it is splitting. These are definite signs of general wear.
The actual breakage happened going downhill. I think going downhill is very hard on the belt. This is because the bike is moving at its own speed, only restrained by the drag of the belt. When the engine is revved up, the clutch engages at 4kRPM (on my stock GEBE 35cc) and the belt is suddenly forced to run at the speed of the engine. This can put a great instantaneous stress on the belt if the engine speed is not matched to the wheel speed (very hard to do), and is definitely a higher stress than just starting the bike from a dead stop.
************ New information added 9/23/07pm ************
With all the discussion that has been generated by my belt breakage observation, I wanted to add a few additional comments
* This is my FIRST experience with a MB. So, part of my experience is to push the design as far as I can to see what the limitations are. Then, I can figure out how to adjust my riding to increase performance or system longevity or whatever.
* My riding includes some very hilly areas. I commonly ride up and down 7-10 degree grades which are rather steep. One of my concerns, from the beginning, was how well the GEBE system could take steep hills.
After breaking my 1st belt, and thinking about why, I have concluded that the premature failure was due to how I engage the engine going downhill. If the bike is picking up speed coasting downhill (steep) and then the engine is engaged at a low 4krpm, the belt will experience a sudden jerk which, after the fact, I now know is too hard on the belt. That explains why my belt broke when I went downhill and engaged the engine.
I can think of three techniques to remedy this -
1) Coast until I am only going about 15mph. Then, engage the engine as usual. This is approximately the speed at which the centrifugal clutch happily engages and is similar to a rolling start. I did this on my ride today and the belt sounds very happy, with no flopping or snapping sounds.
2) Coasting downhill at high speed, then engage the engine/clutch by using maximum throttle all at once (do not use anything less than maximum throttle!). The idea is to make sure the centrifugal clutch is spinning AT OR ABOVE the speed of the bike wheel when engaging. Instead of belt jerk, the centrifugal clutch should slip and push the bike faster, minimizing stress on the belt. This can be tricky because the bike could still be going faster than the motor/clutch can support.
3) Go downhill fast (above 15mph), keeping the engine engaged all the time by giving the bike gas. This way, there is no switching of the clutch from off to on. Since the engine is always engaged, there are no extreme sudden stresses exerted on the belt.
After all this, I think technique 1 is the best for short steep hills, and technique 3 is the best for long steep hills. I am not sure about technique 2...I need to try that in a real world situation to decide.
I wanted to add these additional comments because I didn't want people to prematurely judge the GEBE design harshly because of my firstime experience, without knowing some of the extremes I put the bike through. I am still going through the learning curve of understanding the design's strengths and weaknesses, and adjusting my riding style accordingly. I am expecting to achieve many more miles on the 2nd belt (already 50 miles of hills today with no problems).
). A few times, I pushed the tensioner pulley down to ensure engagement. I noticed some very slight fraying on both sides of the belt. Then, at the start of a casual ride, the belt BROKE. Luckily I was only 1/8 mile from home. This first belt lasted 797 miles but the short life could have been due to my learning process and hilly terrain. See my Intro where I am keeping a log of my experiences (2 entries in this link, latest update is 9/21/07) - http://www.motoredbikes.com/showthread.php?t=5772
