HELP - Harmonic vibration 50-70 kph Mystery!!

Hi all. I have a proper technical conundrum.

Last fall i got squeezed up on a divider in the middle of the road. The bike got delivered into winter storage.
In the spring, i got the shop to change the tyres to new Michelin Road 6.
First ride in the spring. HORROR. A horrible harmonic vibration/shaking that comes from speed of 50-70 kph.
First thought, did they not balance the tyres ?? get them balanced. no effect.
Notice the rims are damaged.
change both rims. Does not help ???
Fork bearing, tighen up, - no effect
It is noticed that the chain is stretched /uneven.
change both sprockets and chain. still no effect.???
replace both tyres with other make, balance, no effect.
Front wheel shaft checked.- straight
Rear axle checked -- no damage.
(Most of the work is done by different workshops)
Vibration is still there .. a cyclic harmonic vibration that is dependant only on speed.

Is there anyone who has any idea what it might be ?

 

something that revolves is bent is my guess

 

Have you checked the disks for run-out? You've changed everything else!

Were the disks rusted during storage?

 

1. Something bent is a good theory, but what?
2. The disks are not rusted. But could be a source of vibration. But how did that happen. Slamming over an edge while braking ? Never heard that it has distorted the disks. And the bike breaks smoothly...?

 

Just trying to narrow down the options but it does sound like something wheel or chain-related. You can easily check disc runout without tools, just raise the front wheel and spin the wheel and hold a screwdriver or similar close to the spinning disc, and see if there are any obvious high spots. Disc carriers are easily bent, but also easy enough to straighten. I agree, a bent disc would also be obvious braking, causing a shudder. When you check the runout you can also look at the tyre and the rim for straightness.

 

Might be. It's at the shop now, hope they will figure it out. This has absolutely destroyed my season.
in my mind the wheels and rims, sprockets and chains are all replaced. The brakes could be, but it brakes smoothly.

Is it possible to misalign the rear swingarm? or the bearing alignment in the swingarm?

 

no possible misalignment on any vfr after 1991

check to make sure the chain is properly adjusted, has slack but not too much.

you inspected rear sprocket cush rubbers ?