Head Shake

[Craft518]

80 hardtail 2" drop 4" stretch with stock forks and wheel. Wheels is balanced and everything is welded straight and the front end is properly assemed. Still getting head shake at around 40-60 mph either on acceleration which can be powered out of or deceleration which I can also clean up with a bit of throttle.

So I'm asking if a steering damper will clean up this minor head shake or is it futile and I should just open the taps a bit when I get a bit of shake. I've never used them before on any bike, sport or cruiser, so I'm interested to see what you guys have experienced with them.

 

[Okie]

Have you checked your steering head bearings? Any looseness there can cause problems.

 

[gggGary]

Cupped tread on the front tire will do it too.

 

[jd750ace]

Running with no front fender or brace is not gonna help either. Your 2 inch drop (I'm assuming that's the rear of the bike) flattens your steering angle and increases your effective trail as well. If you are near the outside of the window (over about 5.5") the smaller things make a bigger difference in stability. Have you done any fork mods? Change oil? Springs? Preload?

 

[Craft518]

So I am running a pretty solid fork brace from Gordon Scott that seemed to help a bit. The forks I am certain are stock through and through. The steering cups and bearings in the head tube have been installed correctly and I see no issue with tightness there. I can only assume the change of angle has a lot to do with the shimmy and the old oil in the forks. Is there a lm advantage to progressive springs and oil change? The weight has been reduced emmensly and since the hardtail has inherently ruined geometry. will the effect of fork springs and oil be noticeable you think? Or am I just throwing money at something that is just gonna shake anyway, and I do understand new oil and springs are always better, but hey I'm not rich! Hahaha

 

[5twins]

My stock bike had a rather vague feel to the front end and a minor head shake in the 35 to 40 MPH range until I changed the fork springs, steering head bearings, and added a fork brace. I can't say this will help a hardtail, but it certainly wouldn't hurt. The head shake may just be part of your creation's "charm".

 

[Craft518]

Also on idle the whole front end shakes quite a bit until I press the front brakes. I've had this before in my Harley chopper too but I assume that normal for a custom application that has been either stretched out front or made ridged in the rear. That's just my experience though.

 

[5twins]

Yes, change the fork oil, and use 7 ounces per leg instead of the recommended about 6. That alone will make a big difference in how the forks work and may help. I'd use the recommended 10wt. too, don't go heavier. If you still have the ball bearing steering set-up, I would get the tapered bearings. This is something these bikes really need.

The shaking front wheel is normal even on a stock 650.

 

[TwoManyXS1Bs]

It might help if you could post a pic of the frontend.

With a camera about 18" off the ground, bike setting vertical, front straight, shoot a pic from the side, of the front end. One pic of the wheel, the ground it sets on, the forks and steering neck, in one shot.

Then we may be able to guestimate the rake angle and trail.

Some combos make for strange handling...

 

[Craft518]

I am going to change the fork oil and add a steering damper. I think these are the best two options. I have also changed to set of handlebars with a taller rise which by some magic has reduced the feel of the chatter. I had drag bars prior and I could feel every single thing. The risen bars reduced vibes and chatter. Thanks for you perspectives guys.

 

[gggGary]

If you get a bad wobble / head shake going.... The guaranteed best WTFDIDN? is to push hard on both grips. Pulling back, no matter how hard you pull, will not help or will even make the wobble worse. PUSHING will damp the wobble out. I do not know if this would work with some dumbass ape hanger bars....

Something about bio mechanics makes the difference. The airplane guys call this PIO pilot induced oscillation. It's real, dangerous, and sometimes fatal.
Then get it off the road find the cause and FIX IT.

Random cheery thought of the day.
Monday evening after a long Labor day weekend, at an intersection very near my house. Two guys on a sport bike stopped at a stop sign. Their "buddy" following behind in his jeep didn't stop till he hit a retaining wall 300' past the intersection. Rider died in the helicopter, passenger is still critical. A policeman friend of ours held the rider and tried to console him as his life ebbed away. No helmets, all had been drinking.
A little boy now has no daddy. Think his life will be different?

Be safe out there.

 

[grizld1]

Listen up, Craft. Headshake and steering wobble (oscillation) are not the same thing. Headshake occurs when the bike encounters a dip or other irregularity in a corner and a hard tweak gets delivered to the steering head. That's what steering dampers are designed to correct, and that's not what's going on with your machine. The only way to get rid of oscillation is to troubleshoot the whole frame and suspension, including tires. At least you know how to break the wobble, which puts you ahead of 98% of today's riders.

 

[Lleonardo]

Did you ever fix the problem? I have a 1980 XS650 hard tail and have the oem front end and having the same problem headshake I guess what you call it. Put a new set of tires thinking that's going to fix it but it didn't

 

[gggGary]

1980 XS650 hard tail and have the oem front end and having the same problem headshake I guess what you call it. Put a new set of tires thinking that's going to fix it but it didn't

picture of the bike!

 

[TimeMachine]

2" drop & 4" stretch.. suspicious handling right there. Now are you sure your wheel alignment is correct ? Rear wheel spacing is correct ? Roll straight onto a line on the shop floor, check carefully for alignment. Could contrubute. RT

 

[mrtwowheel]

You can rule out swing arm bushings and rear shocks. Are your motor mounts tight? Do you have all of the motor mounts? The stock upper motor mounts are known to break.

Scott

 

[Exploding Coffin Emporium]

Lleonardo, When you got new tires did the problem get better for awhile, stay the same or get worse? Have you checked your bearings? Is your axle and wheel true? Who did the hardtail, you or a pro? What condition are the forks in? How's your fork oil? Springs? I know I've asked a lot of questions and hopefully with your answers we can rule a lot of these problems out and pin it down, send pics and info, cheers

 

[BobbedSled]

Not sure if you lowered the front, but if not try this simple test, try sliding the forks 2" up the tripples and see if that corrects it. If everything is true it should and you can assume the frame mods are good you just introduced some geometry issue. If not there is something else affecting possibly frame geometry issue as a result of the build.

I used dampers a lot and they work... but they have to be rebuilt frequently so just be aware. There is so little oil in them it breaks down quickly. But they are awesome, I used Scotts Stablizer.

 

[Lleonardo]

picture of the bike!

 

[Lleonardo]