Bike starts to shake over 85 mph

[Ndulucky13]

So just finished fork rebuild so had it on the highway this weekend for the first time.  Glass smooth until I approach 85 it begins this shake not in the bars but more an up and down shake not horrible but defiantly noticeable. Tires look ok I have no clue what it could be?

[red]

So just finished fork rebuild so had it on the highway this weekend for the first time.  Glass smooth until I approach 85 it begins this shake not in the bars but more an up and down shake not horrible but defiantly noticeable. Tires look ok I have no clue what it could be?

Ndulucky13,

Sounds like a wheel balance problem.  Even a wheel with good static balance may go shakey at speed.  Put the bike near a wall, on the center stand.  Pivot the bike on the center stand until the bike and front wheel will be solidly head-on, touching the wall.  Start the engine, run through the gears, and see if the shake is caused by the rear wheel.  Do not overdo this test; if the rear wheel is at fault, kill the engine right away and fix the problem.   If the rear wheel is causing this, check the wheel balance, and maybe even the bearings of the wheel and cush drive.  Pivot the bike away from the wall, to get it down from the center stand.  I do not know any DIY way to check the front wheel at speed, but if the rear wheel checks out good, then try balancing the front wheel.  Keep us posted.

Cheers,
Red

[markmartin]

It does sound like it could be a wheel balance problem.

Can you elaborate on what the fork rebuild consisted of? I'm assuming seals and bushings, but do you still have the damper-rods in the forks or did you install emulators ? If the damper rod is not inserted through the D shaped hole, it can still be assembled but will really **uc up the front suspension.   BTDT.

Also, I'd want to confirm that the fork tubes are set at the exact same height above the triple clamp. ? And that all bolts on the top and bottom triple tree's are tight. Basic, I know, but in an effort to eliminate the obvious....

[Ndulucky13]

I relplaced just the seals with only 14k on the clocks the bushings seem good.  Both forks are exactly .75 inches above top triple all bolts are tight.  Air gap set at 5.5 inches with 10-40 motor oil as I found on the web that is the best for handling. Preload is set at 2 turns is that to much? Damper rods are correctly installed how could you install that incorrectly? It's bolted through the bottom leg.

[markmartin]

Damper rods are correctly installed how could you install that incorrectly?   It's bolted through the bottom leg.

My bad.  The damper adjusting rod is what I should have typed, not damper rod.  You're right, the damper rod is bolted to the bottom leg.

I was referring to the damper adjusting rod which gets inserted in the top\center of the damper rod.  It can however, be inserted (inadvertently) into the slots at the perimeter of the damper rod.  I've done it--not proud of it    If one or both of the damper adjusting rods are misaligned like this the suspension will only compress about 1" and this would probably cause a problem when driving fast or over rough roads.

I'm still with Red, I'd check the balance on the front tire first.  I know some people don't' bother to balance street M/C tires but I always do.

My only other thought is that I think 10W40 Motor Oil is about 3 times as thick as a 10W fork oil.  I've read of it's use in front forks before, but it just seems awfully thick and that could be affecting how the suspension is cycling at 85 - 90 mph.  Again, these are thoughts, not theory.

[Ndulucky13]

I'm a little nervous now I didn't have any damper adjusting rods?  Do you have a picture? Here is mine tore apart

[markmartin]

Check out this link for a diagram of the front forks.  # 24 is the rod --it's part of the top fork cap assembly.  I'm not seeing it in your picture...
  http://www.yamahapartshouse.com/oemparts/a/yam/50042dbbf8700209bc78a11a/front-fork

Check out this old post in the suspension files for some close up pictures of a stock and modified fork assembly. A good picture of the damper adjusting rod can be found close the the end of this write up.

http://www.fjowners.com/index.php?action=dlattach;topic=1911.0;attach=594

It's hard to tell from the picture, but the round part located between the fork lower and damper rod at the bottom of your picture looks like a cartridge fork emulator.  This would be a good thing and explain your missing the damper adjusting rod as the rod has to be cut off when installing cartridge fork emulators.   

If this is the case, emulators are an upgrade to the damper rod suspension system, so very good for you.  But from my experience, I've had better luck with low viscosity fluid when using emulators.  I don't know if it would cause your front end oscillation but it would be interesting to know what you've got for front suspension components.

Can we get an up close picture of the aforementioned part??  eerrh...yeah it's probably in the fork now...  Did it drop in on top of the damper rod and under the spring?

[racerrad8]

All the correct parts are there he has the later model forks. They do not have the damper rod. the pre load is adjusted directly to the spring from the fork tube cap.

Robert

[markmartin]

Oh, perfect. Thanks Robert!  Nduluckey13, sorry for the needless concern.

[Shane4371]

I relplaced just the seals with only 14k on the clocks the bushings seem good.  Both forks are exactly .75 inches above top triple all bolts are tight.  Air gap set at 5.5 inches with 10-40 motor oil as I found on the web that is the best for handling. Preload is set at 2 turns is that to much? Damper rods are correctly installed how could you install that incorrectly? It's bolted through the bottom leg.

it does bolt down,however it has a specific position the rod has to be it.theirs a slot that lines up with a threw scew.that slot goes over the screw.if not the rod won't be bottomed out

[Ndulucky13]

Ok that last post confused me a little. You are saying that the damper rod lines up with something?

[markmartin]

No. You're all set. My fault for getting this thread going down a rabbit hole that doesn't exist. You don't have the damper adjuster rod in your model. I was referring to earlier models that use the damper adjustment Rod. Robert identified your fork internals as not having that damper adjuster rod.  I didn't know the later models don't use the damper adjusting Rod but rather the spring to adjust damping in your forks. If you did have a damper adjuster rod like the earlier models it is possible to Assemble it incorrectly. It looks like we're back to an out-of-balance front wheel?

[4everFJ]

All the correct parts are there he has the later model forks. They do not have the damper rod. the pre load is adjusted directly to the spring from the fork tube cap.

Robert

Just curious... Preload adjustment I get, but how is the damping adjusted in the later model forks?

In my experience, wrong damping adjustment can also make the wheel bounce.

Looking at the parts in the photo, my guess is that there is no damping adjustment and that damping relies on oil viscosity(?)

[racerrad8]

There is no dampening adjustment on the later model forks.

On closer examination of the photo the plastic spindle taper is missing. If the taper is installed upside down it is probably stuck in the lower fork leg.

The first three photos are of the taper spindle installed correctly on the damper rod and in the end of the fork tube. The last two are the taper installed incorrectly.

Robert

[Ndulucky13]

There was a bushing I'm assuming the plastic one in photos in the bottom of the fork.  I couldn't tell if it came out or not and didn't want to break or bend it so I cleaner the lower leg with it in place.