Bouncy front end

[Vetschoolpiper]

Hello,

I recently replaced the fork seals on my 82 Honda CB 650 and ever since, the front end has a little shimmy to it and there is a bounce in the front end that is really noticeable at slow speeds, say under 40 mph. Everything seems aligned and tightened. Any ideas as to what might be going on? If there are suggestions for a fix, I'd like to hear them too. Anything I can do at home would be best, I can't afford a shop at the moment.

Thanks,
Bryan

 

[Patrick]

When you replaced the seals did you use the correct weight of oil and the correct volume?

Patrick

 

[Vetschoolpiper]

yeah, used what my service and repair manual said to, as far as volume and type.

 

[Tourmeister]

You mention shimmy and bouncing. Do the forks go up and down a good distance at low frequency or are they chattering up and down a short distance at a high frquency?

Bouncing is a lack of damping. Either the oil is too thin and thus does not resist movement of the forks, or you can have too much air in the fork (not enough oil). The air is compressible and will act like a weak spring. When you changed out the oil, if you did not stroke the fork to "bleed" out the excess air, you may have too much air in the fork still. The other possibility is an under inflated front tire, but that would make the front end feel sluggish to turn as well.

Welcome to the site. Where ya from?

 

[txbanditrydr]

You might consider checking the steering head bearings for proper tightness... just a thought.

 

[kurt]

When you changed the oil did you pump the fork legs to get it below the valving? If not, and you measured it by height instead of volume, you could be seriously low on oil. Not that I've ever done that.

 

[Tx Rider]

You might consider checking the steering head bearings for proper tightness... just a thought.

Ditto.

 

[Vetschoolpiper]

Okay, to follow up. I decided to drain and refill the fork legs, just to be sure. Exact volumes in each leg and everything is aligned and tight. I guess I should describe the bouncy symptom better. The front acts like the wheel is out of balance, because the forks seem to dampen as expected when I go over a bumpy section in the road. It is just as I get up to about 35-40 mph, the front begins this bounciness and I watch the forks and there isn't any travel as far as damping effect. This happens even on a relatively smooth stretch of road also. The shimmy is subtle but enough that I can feel it. I can go slow and let the handle bars go and the front end shimmies and wobbles.

Tourmeister - I am a 4th yr veterinary student at A&M, and I live outside Bryan. I got turned on to the site by a bagpiping friend and student who rides.

 

[Tourmeister]

Whoop! Class of '91

Have you checked the balance of the tire? That would generally cause an up and down pogo feeling. Steering head bearings usually cause side to side instabilities like like frequency weaving (too tight) or high frequency shimmies (too loose). It might be worth taking the bike to a reputable mechanic and letting him ride it up and down the road a few times to see what is happening. I don't personally know of anyone in the BCS area. Patrick's shop is on FM 1960 a few miles West of I-45.

 

[redrider4life]

Take the tire off and bring it by. Ill check the balance for you.
Ron
Greathouse Motorsports
903 South Main
979 823 0545

 

[cmcnamee]

I'm assuming that the bouncing of the front end started after the servicing. Like others suggested, check the front tire's balance first.

If the tire is balanced, ensure that the forks are the correct height in the triple clamp. They may not necessarily be the same height in the triple clamp when installed correctly.

What I do is install the first fork in the triple clamp at the specified height. Then I loosely install the second fork. When I think it is close to the right height, I slide the axle into place and ensure that it slides in easily. If it does, then everyting is alligned and you can tighten down the triple tree. If the axle binds while sliding into place, even a little, then adjust the second fork up/down until the axle does slide in easily.

Carl

 

[Vetschoolpiper]

Take the tire off and bring it by. Ill check the balance for you.
Ron
Greathouse Motorsports
903 South Main
979 823 0545

Thanks Ron,

I'll come by when I can. Vet school schedules can be rough to work around.

Bryan