Hi there,
just reading your thread.
Chain jerking around without load on it on a 550, seems normal to me as both mine done the same slapping on plastic guides and front sprocket sat a bit loose on spline , mine had done lots of hours work though .
Try elevating the rear wheel off the ground or up on bike stand off the ground.
Sit a screw driver or bit of wood or some object on the swing arm and touch it against the edge of the rim whilst resting on the swing arm , and have someone spin the wheel. Check if there is much deviation of the rim like a side to side buckle , twist or up and down buckle of the rim.
The rim should turn and the gap between the wood block or object resting on the swing arm sitting close to the spinning wheel should not change to much, maybe a couple of mm. If it is 10-15mm , may be the problem
Now hold the object close to the tyre and do the same, if you see lots of up and down or side to side movement of the tyre, maybe the tyre bead isn't quite on or interfering with the rim lock or the tyre may have a defect causing vibration.
Check the front tyre and front rim the same way by resting something on the fork leg holding against the rim then tyre looking for abnormal movement.
Try 30 psi in both tyres, ride, feel what its like, then let the rear one down to say 5psi on flat level road surface at the speed, see if it vibrates, if it changes , or vibration lessens, then that has isolated it maybe to the rear wheel or tyre.
30 psi in rear tyre again,try the same thing on the front tyre and feel for change, be careful low pressure in front tyre wont steer to well or stop. If the vibration lessens, then maybe you have isolated the issue to front rim or tyre.
If you still cant tell, process of elimination, change the front tyre, still no change , then swap the back tyre with another one. You can do this with any old tyre if you like.
If there's no change and its still vibrating, then its not the wheels or rims.
Not sure what else to look at for that
Hope that helps some
