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Hi guys, ive been wanting to ask this for so long but i hadnt found the new forum until now. Ive been using the bike everyday to go to college this year since i started studying and it means taking the freeway every day, ive packed on quite a bit of milage since i rebuilt the bike completely last year and i think i have put on about 6000km since rebuild which included getting the front forks completely serviced(new oil and seals), anyway to get to the problem, the bike rides smoothly until about 140km/h and then after that the front starts to shudder and i can actually see the front wheel and forks vibrating, the mudgaurd which i spent so much time repairing is again rubbing on the tyre with the shuddering and its eating the mudgaurd again, its a horrible feeling, and i dont remember when it actually started because i normally just cruise with the bike on the highway but i remember after i ran in the engine i could take it to 180km/h no problem and it was smooth and comfy.

any thoughts? i was thinking maybe i should drop the forks lower for more stability? However when i rebuilt the bike i made sure everything was to service manual specification, i took special care in making sure i installed the forks to its stock height and measured everything multiple times to make sure both were equal etc, and also the forks arnt leaking oil and they still rebound as they always did.

could be tire pressure too low or freeplay on the front BUT also on the rear swingarm and wheel.

Have you had your front wheel balanced ?

I havent actually checked tyre pressure in ages, i will check that later today and make sure its on FSM spec, and the wheel wasnt balanced when i got the tyre put on, they said it did not need balancing but they did balance my rear wheel, but i dont think its balancing, its not that kind of vibration, its a shudder where its almost like the forks are flexing forwards and backwards like in the direction of this photo:



the service manual says check headstock bearings, but when i rebuilt the bike i made that tight enough according to FSM, and it doesnt feel like its loose there atall, and i dont feel the shudder on the handle bars, i can physically see the movement of the forks while going that speed.

Troopiec wrote: i can physically see the movement of the forks while going that speed.

Stop looking!

Troopiec wrote:its almost like the forks are flexing forwards and backwards

Neck bearings?

Yatsushiro wrote:Stop looking!

lol i dont need to look to feel the effect, its a horrible vibration, really bad, i just looked down the one day and saw how it was moving.

Hi Troopie ,

there are many problems here , if they said the front wheel does not need to be ballanced the were talking kak . Push the pads apart on the brake calliper , lift the front of the bike up and spin the wheel . Make some marks where it stops , if you can see it is out of ballance like that then it will be worse on a proper ballencer .

Double check the headstock nuts , when you install new bearings etc the settle over time and the nuts need to be nipped up again .

We live in a special place that has potholes on freeways , live roaming animals on freeways etc so expect the roads to be bumpy too .

If those things don't rectify the problem , then obey the law and ride at 120 km/h Eish - rather look for those vibes man and ride it flat out !

I had a similar problem with my 1KT a few years ago when the wheel balance weight had fallen off the front wheel and my forks were shuddering.I only noticed later that the balance weight was missing and once the wheel was balanced with a new weight the shuddering had gone.

Neal wrote:Double check the headstock nuts , when you install new bearings etc the settle over time and the nuts need to be nipped up again .

Yep. First time I did head bearings it took me 3 attempts to get it right. Set them up, go for a quick spin come back and redo them.

Also if they are a problem it might not be obvious when checking unless you know what you're looking for. To explain I checked mine and didn't think there was a problem, took it to a local bike shop who checked and told me they were off. But with someone there to go through it with me and say "that tiny little notch is what your problem is" and remember, don't use much pressure/ force when moving the forks around when checking as that can mask the problem.

Also to reiterate what has already been said, the rear could also be the problem. Check swingarm and linkage bearings as if these are not working properly then you can find problems at the front end.

I would also check the wheel balance again, as it not needing a balance doesn't sound right to me. And how old is the tyre? I had an interesting issue on a Blackbird with a front tyre. Apparently it wore on one side more than the other which gave a little little head shake under breaking (not fun on the road, interesting on the track). Tried to rebalance it but it was only solved by replacement...

Get a mate over. Put the bike on side stand and turn bars to right. Get your mate to stand behind the bars next to the side stand and to pull on the bars which will lift the front up. Grab the fork legs firmly at the bottom and perform the test in the pic you posted. If there is even a slight movement you need to reset head stock.
That test is free.
Next is to get front balanced and i would go to another bike shop as the first lot might lie again to you.