front end vibration

Hi,
Just was curious if anybody has any ideas for me. I have a 1981 kz650 csr, it has a rhythmic bouncing in the front end, or at least it feels that way. I needed to replace the fork seals anyway so I changed them and the oil and adjusted air pressure, no difference. It seems to be worse at lower speeds than cruising, and it does it on a brand new perfectly flat road. any possibility the chain and sprockets would cause this? Also front tire is new and balanced, and everything seems tight.

Thanks

Chains and sprockets can develope tight spots. To check this,put the bike on the centerstand(if you have one) and spin the back wheel looking for out of round condition on the rear sprocket.

Have you spun the front wheel, again looking for an out of round wheel? Possibly wheel bearings are going.

rear wheel straight in the swingarm?

Sometimes when you mount a tire, it can be seated wrong when you pump it full of air. There is usually a raised line moulded into the tire that is right where the tire meets the rim that will show this. This is usually not the case if it has been balanced correctly. If a shop did the work it would be worth checking.

Just curious.....Is the steering supposed to "detent" to the center position. Mine does this and I am wondering if this could be causing my problem.

Thanks

explain detent....more details

fyrfyter1804 wrote:

...1981 kz650 csr, it has a rhythmic bouncing in the front end...worse at lower speeds than cruising, and it does it on a brand new perfectly flat road...

Just curious.....Is the steering supposed to "detent" to the center position. Mine does this and I am wondering if this could be causing my problem....

"detent" to the center position may indicate the ball bearings in the steering stem are no longer rolling smoothly in their races. Tightening usually doesn't remedy the condition. Many owners have converted to tapered bearings for better longevity. However, could be wrong but don't suspect the "detent" is causing the rhythmic bouncing in the front end.

Perhaps a warped front brake disc rotor might possibly cause the brakes to drag and produce a pulsing sensation.

As earlier mentioned, would look at front tire mounting, and balance, and assure tire isn't out-of-round. All in addition to the drive chain condition and alignment, and rear wheel matters previously noted.

Good Luck!

fyrfyter1804:
I had the same problem that was most noticable at about 40 MPH. It would practically go away below 25 and above about 50. Both tires had been balanced. The front tire was out of round by about 1/16", more on one side than the other. The rear tire was about 1/8" out of round and somewhat irregular when rotated.

Then I got new tires and wheels. THE PROBLEM COMPLETELY WENT AWAY. The previous wheels ran very true, so it was not the wheels. I put the old front tire and wheel back on - no bouncing or wobble. Took it back off, put the new front tire on, and put the old rear wheel & tire on - The wobble was back!

So my wonderful Kenda Challenger rear tire was causing the front to wobble up and down. The tire must have also had hard and soft spots around the circumference, in addition to the out of round. With the new tires, the whole ride is so much more pleasant and controlled.

The steering detent situation is where the balls eventually beat small notches in the bearing races, mostly in the straight ahead position. This occurs due to riding on rough roads, or out of round or out of balance tire, or, as I did, by over tightening the steering bearings. This might slightly aggrevate the situation, but I do not believe is the primary cause of the wobble or vibration. Mine has this and I plan to install tapered roller bearings soon.

The Kenda Challengers gave high mileage, and average traction, but were not manufactured to very high standards regarding roundness and uniformity, in my opinion. Hope this helps.

Might be time to do an engine tune-up,synch carbs,adjust valves etc.

Sound like everyone has got you covered. Just one thing I know of I rub my hand oner the tires and can feel flat spots or bumps they should feel smooth plus a visual inspection. I found a lot of shakers on bikes and cars.