Hi-speed head shake

[201mph]

While merging into traffic from one Interstate Hwy to another I cracked my throttle wide open from about 45 in 2nd gear and zipped to 90 a couple of seconds later when suddenly my front end started a wicked shake. I munched down on my rear brake(along with my sphincter muscle) and it stopped almost immediately.I have just adjusted my suspension stiffer for my almost 220 lbs. by setting the front preload with 2 1/2 lines showing,and the compression and rebound out 2 clicks.The rear has 1 1/4 sag with comp out 5 clicks and rebound out 7. This was an older section of highway with expansion lines and cracks, but I have been through there a number of times in almost the same manner with no problem. My question is; do the stiffer settings make the front end more prone to such antics or are there other variables at play here? One of the things I love about my Busa is how stable it always is, and I have not encountered any head shake in the past. Most of my fast riding has been more in a straight line to this point though, and I was swinging out and around some slower traffic when it started the shaking. Thanks for any opinions!

 

[OB_Johnnycheese]

Start with the basics tire pressure axle torque front and rear steering head bearing adjustment are you using OEM tires?

 

[201mph]

JohnnyC; the dealer did the adjustments as part of my service this week. Stock Bridgestones, tire pressure 42/42.What do you recommend on axle torque and rear steering head bearings and/or how do I check to see they are set right.One more question- Have you had yours ever shake (with the stock suspension if you've changed it?)Thanks!

 

[OB_Johnnycheese]

yes I had tighten the rear spring one turn and in a high speed corner I got a wobble but not a head shake backed off half a turn and felt fine.the toqrue on the rear axle is the same as the front 72.5 ftlbs the steering stem needs to be adjusted with a fish spring scale and then the crown nut is torqued to 65.0 ftlbs.
this is a tough subject to do with out having the bike to test ride and see what is happening.I sujest to take it in to the dealer/or someone who is COMFORTABLE working on this type of problem.

 

[201mph]

Thanks, I will if you thinks it's totally uncharacteristic of the bike.I just know that I haven't had it on the Busa before, but I got my bike at the very end of December and I still have less than 1500 miles on it.I had an old Kawasaki 750 H2(3 cylinder, 2 stroke)shake at over 140 one time and it scared me big time.I still remember wondering if it would shake me off!I even drove slower for a week or two, If memory serves me.By the way; Whats a fish scale and does every dealer have one?

 

[Frank Adams]

I had it happen so bad it through Me off the bike going 120 mph.

Turns out the bearings in the steering head were loose.

I wouldn't take another ride if I were you untill you check this and other things!

I was told by one of the best frame makers around that making the settings stiffer shouldn't cause any of these type of problems. In fact, he said he's made frames with no suspenion at all and never had anything like that happen.

I'd do your checks if I were you.

 

[sherm]

Even if all those things JC mentioned are off wouldn't the steering damper prevent headshake? Can the head shake with a properly working steering damper?

 

[OB_Johnnycheese]

no the streering dampner will only help them not be violent,it wont stop them,all Suzuki dealers should have one(scale)don't hesitstate to ask questions of the dealer and like I said find someone who is comfortable working with you.and when you go in have a list of excatly when and where the head shake occured,ie which gear,rpm,mph,location,both hands on the bars,
ect.

 

[201mph]

Thanks. I guess the damper saved me then cause it was fairly wild.I slowly took it up to 140/150 on a very smooth and wide road and it shows no problem.I guess that's no indicator necessarily since the uneven road surface is what seemed to get it started.I will have them check it out.

 

[OB_Bob Lynch]

Frank, tossed at 120mph! OUCH!!!! Glad your all right and still rideing. BOB

 

[OB_Bob Lynch]

201, Sorry I went out of town, and we didn't get to ride. Sounds like you had your hands full. Question, were you rideing on a concrete road when snapping the throttle. I got my XX out of shape once when the suspenion got lite from the uneveness of the road. I also got head shake on I-40 rideing the busa. Both things incommon were the concrete road bounceing the suspenion during during heavy throttle in low gears. Just food for thought. Give me a call! Hey, who does this guy eagle cop think he is droping that kind of threat to all that ride in norman. Did you check his profile, he's only posted once, and that was one to many.

 

[OB_Velociraptor]

All of the above suggestions about steering head bearings, etc are good, but I'm wondering if you just got the front so light that the combination of turning and weird pavement did it. If that is a possibility then reducing the rear sag should put a little more weight on the front and keep it from getting light so easy.

 

[OB_GSXRboy]

I know on my 98' RR when I used to get on it hard the front end got real light and it was real prone to the headshake. All it takes is a few cracks in the pavement and a light front end and the tire will follow! I haven't had it happen on my Busa yet but I will cross my fingers that it don't. FYI: I cured it for the most part on the RR with a steering dampner.

 

[201mph]

Yes it was on concrete, and it was at I-40 and I-240 junction. It is a weird patch of pavement and I was accelerating as fast as it would go. Still, their are a couple of things I need to check on the bearings it sounds like.

 

[201mph]

Thanks for all the tips.It was VERY light in the front at the time, almost skitering over the road surface because in the power band in second it's very fast as you all know. I think the inch and a half sag in the back is making it a little lighter in the front than I had anticipated. I am going to the old House OF Kawasaki and Suzuki (I KNOW Suzuki should be first but what can a man do?)today and if we don't find any other mechanical problems than I will change the rear back some to a softer setting.

 

[OB_Bob Lynch]

201mph, Home already! If the weather is good, I'm in for a morning ride.

[This message has been edited by OKLAHOMA BOB (edited 07 March 2000).]

 

[201mph]

I'll call you. But I do need to take it by the shop, i guess, before it rains. Maybe it will hold off till tomorrow night!

 

[201mph]

I took it by the shop, and after checking everything for mechanical problems we finally noticed that it was too low in the rear. We bumped it up again and it is 100% better. I thank everyone for taking the time to answer my question. As Velociraptor and several others had surmised, it was getting too light in the front. I'm back making those over 150 romps that MUST be the reason they named it after a bird! It is an incredible machine. It even SWOOPS!

 

[OB_Bob Lynch]

Not a swooop, it's just fly's!!

 

[AQUADIOSMED]

Hey 201:
did you check ... as in the Suzuki manual ... with the "springs for correct steering stem bearing tightness"???
you might be right, just too low in the rear, but it sounds as if the steering stem bearing might be a little "loose";
might want to check "sag" while sitting, in the seat, with all your weight, yours may be too weak, thus, too low???

Alan