High speed vibrations

[Fazerjon]

Hi people, just wondering if anyone else has experienced high speed vibrations on a Gen 1 thou that start around 100 mph upwards (at the Isle of Man before anyone starts saying anything!) I’ve checked wheel bearings, head bearings, swing arm, replaced chain & sprockets, checked engine mounting bolts, tyre pressures, etc but all ok. I took the wheels to my local tyre fitters just to re check the balance and all is ok. I don’t think it’s an engine internal vibration as it pulls through all the revs to the red line no problem. I’m stumped for ideas now. I’ve checked the mirrors and fairing mounts too. The only change is new ish (400 miles ago) Michelin Road 5 tyres. Never really noticed it with the 4’s.

[old son]

So the obvious answer would be tyres?

[Fazerjon]

Well that’s the only thing left I think! Just thought I’d put it out there in case I missed anything. Wonder if anyone else has had similar issues with Michelin Road 5 tyres?

[Trebus]

Have you checked the sprocket carrier bearing is OK? Are the wheels / tyres being dynamically balanced or static?

[Fazerjon]

Yup, checked all bearings. Just changed chain and sprockets as they were well worn, so while it was all apart I checked the sprocket carrier bearing too. Wheels were balanced on the tyre garages machine that spins the wheel with the new tyre up to a certain speed , so not statically balanced. I’m stumped…

[Gaz66]

Howdy ...
Have u confirmed wheels aren't buckled in any way or out of round?
Dynamic wheel balancers are far from perfect, used em for last 40yrs, on both bikes & cars, if not correctly calibrated (most aren't) you'll never balance out a heavy spot.
Personally I've found the cheap home balancer to be accurate enough, never had any vibes using one.
Did you get wheels balanced with both discs fitted, if not, there might lie the problem, any rotating mass needs to be balanced.


Check tyre is seated correctly on rim & is in fact a true/round tyre, u may have fell foul of a dud tyre.
Check fork legs aren't bent, this can put stress in the front end & mask as vibes at speed.

[Fazerjon]

Thanks for that, I have a static balancer I’ll try that as my next port of call. All wheels were balanced with both discs and rear sprocket fitted.

[Gaz66]

Hi.
What I've found from experience with static balancers that the bearings drag a bit, I removed the plastic dust seals & wash out all the old grease  lube em with engine oil, it can make the difference between finding a heavy spot or not.


Is your bike tuned in any way, vibration might be from the motor, carbs set wrong, wrong jets etc, hope the crank ends not bent at flywheel side, seen a few bikes with bent crank ends from previous crash damage or ham fisted hammering to get a tight flywheel off.
Is this vibration at any particular speed? if so, does it still occur with no load (clutch in) etc?

[Fazerjon]

Hi yes mildly tuned, full Monty Ivan’s kit fitted by Mike, MotoGP slip on end can, Pipercross filter and that’s about it. It’s been fine for years, I balance carbs yearly and she pulls through to the redline cleanly in every gear. At around 105-110mph the vibration starts. If you keep the throttle pinned you can ride through most of it. It also has 2002 R1 USD fork conversion but easily hit 160 before with no vibes. I’m veering towards the Michelin Road 5 tyres now as there’s not much else left to check. Bit annoying as they’re bloody new tyres!

[Fazerjon]

Well I think I’ve found the problem at long last. The fork bushes seem to be worn as there is play in them. I could feel a bit of play which I initially thought was head bearings but they’re greased and adjusted correctly. So I took the forks out and sure enough there is play in them. Once I’ve replaced the bushes I’ll report back hopefully with good news!

[SkidT]

Fingers crossed you’ve found the source. 🤞

[Trebus]

Hopefully not too bad to sort.