Yager - significant vibration over 55MPH

[Zimmerman]

It is a general vibration felt through the seat and floor - but not especially through the handle bars.
I've not driven the scoot over 60 MPH and it doesn't vibrate under 55 MPH.
It is enough of a vibration that I'm concerned about safety.

Here's what I've tried:

   - I adjusted the rear shocks: hard, soft and in between - no effect - there is a noticeable vibration from 55MPG up to 60 MPH.

   - The front tire pressure was a little low - fixed that - same vibration.

   - Installed Dyan Beads - front and rear - same vibration.  (Thought it might have been tire balance.)

   - Coasted down hill with engine off - only got up to 35 MPH - didn't hear/feel anything.
     If I can find a big enough hill with a smooth road surface and little traffic - I may try coasting again @ 55+ MPH.
     It's hard to hear with a full face helmet (if there is anything to be heard.)


The vibration seems to be MPH related rather than RPM related.
I say this because I run the engine at all RPMs as I accelerate - no there is no vibration until 55MPH.
At 55 MPH the RPM is ~7K

- -

Any tips on how to isolate the cause (or eliminate possibilities) would be great.


How would a bad wheel bearing behave ?
Would it cause vibration at only higher speeds ?
How can I test for a bad bearing ?

What does drive belt slap feel like ?
Is it speed related ?
How could I test for that ?

Would it hurt the scooter to run the engine at 7K RPMs on the center stand ?

I really wish I could run it on a Dyno Belt.

 . . . Kevin

[streido]

Engine mount loose?

Belt could be hitting the starter bendix at 60mph too depending where it sits.

[Zimmerman]

Thanks - I will check the engine mounts.

Also someone else suggested I check for an out of round tire.

I appreciate the feedback.

Once it's fixed I'll be sure to post the answer.

Kevin

[Zimmerman]

The problem is in the rear wheel / tire.

On the center stand at ~6500 RPM you can visibly see the wheel moving up and down.  Also gently placing finger tips on either side of the wheel (near the bead) you can feel the wheel wobble side to side.

I'm going to rig up some static jigs so I can slowly rotate it by hand - using te jigs to 'see' the problem.

Testing ideas welcome . . .

[streido]

The problem is in the rear wheel / tire.

On the center stand at ~6500 RPM you can visibly see the wheel moving up and down.  Also gently placing finger tips on either side of the wheel (near the bead) you can feel the wheel wobble side to side.

I'm going to rig up some static jigs so I can slowly rotate it by hand - using te jigs to 'see' the problem.

Testing ideas welcome . . .

Finding the problem is usually half the battle, so youre half way to fixing it now 

[Zimmerman]

Thanks - I do like a good puzzle, especially when looking back.

Also forgot to mention did same tests on our People 150 - no up / down motion - no tactile side to side wobble either.

[Zimmerman]

Ok the digital dial indicator says:

Yager
Wheel (near bead) varied from -0.40mm to +0.53mm
Tire (side wall) -0.63mm to +0.1mm

People 150 (doesn't have a problem - used for comparison.)
Wheel -0.13 to +0.1mm
Tire 0mm to -0.38mm

Randy said the run out spec was 2mm - both these scoots are within that spec, but the P150 is tighter.

Next I'll check to see if the rear wheel is mounted perfectly on axis with the center of the bike.

(This may just be a defective rear tire, but I like to be sure before doing the work.  It's a bear getting the rear tire off of a People 150.  Is the Yager just as bad ?)

[Zimmerman]

Ok this is interesting and unexpected. . . .

I took the rear  brake ass'y off and secured it to the muffler stand offs.
I ran the scoot on the center stand - just looking at the rear wheel, it still appears to be bouncing.

The surprising thing was, when I took it for a test drive ( without a rear brake ) I went as fast as 65 MPH without any vibration.

Later I'll use the dial indicator the check the braking disc for run out.

If that's good then I think the side to side movement of the wheel/tire is more than the uncompressed brake pads can handle.  Apparently the disc is hitting the pads enough to cause vibration.