Fixing the speed wobble problems 2

[TurbineGen]

In the last few years I've had issues with older 4 cylinder Japanese motorcycles becoming unstable above 75 mph. The years where this was the worst are between 1975-1984. Several of the bikes had ecessive play in the swing arms in the rear which needed to be ground down (namely the Honda cb650 and cb650 Custom models), but they still retained the speed wobble. I tried replacing the head bearings in some that had cut tracks in the bearing race and replaced them with roller bearings. Again they still had a speed wobble, but this pushed the speed up from 50 to 75 or so before the wobble came back.

I cannot for the life of me figure out how to correct this problem. I've tried everything I can think of and am coming up short. The only thing I can think is that maybe the forks are too small and are flexing at speed. All of the bikes that wobble appear to have smaller fork tubes and no fork brace. Would fitting these with fork braces help prevent this? I have been restoring classic bikes for some time now and this issue I can't seem to correct.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[dgallup]

There can be a lot of causes. Worn tires, loose wheel bearings, loose suspension pivots, etc. Have you checked the shocks & forks? Both may have lost most of their damping which was usually underwhelming to begin with. Some of the '70's bikes were pretty unstable to begin with, particularly the Kawasaki 3 cylinder 2 strokes.

 

[TurbineGen]

When I do a restoration, the tires are replaced with a high quality tire (usually Pirelli or Dunlop), I check the wheel bearings for excessive play and repack them with grease if they are acceptable. All of the pivots are tightened and inspected for excessive play.

Damping is something I hadn't thought about. I usually replace the fork oil with ATF, which is a 5 weight oil. Since the manufacturer recommended a 5 weight I figured Automatic transmission fluid would be fine. Should I try a heavier oil?

This wobble problem is driving me nuts. It's one of those historic issues I can't seem to fix.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[evelrod]

I understand what your saying and all the "proper" restoration tips seem to be commonly done on most of the "old" (really, kinda new from my point of view) Japanese bikes.

Well, to start, the handling of those 70 era Hondas were CRAP and if you had crap when new, why would you expect anything better in a restoration?
I had a 72 Yamaha 650 that shook it's head at anything over 70 and even with new forks, swing arm bushes, Michelin road racing tires, Girling dampers, it STILL shook, just at 90 !!!

Now enter the day of the Z-1 and the KZ-650 Sport. Never had a problem with any of them including my 77 KZ that I rode to Mexico City, two up. Even my 81 Goldwing was not a head shaker at any speed. From that I figure the Japanese finally found out how to make a street bike handle. Hope so cause I have not ridden anything Japanese except my son's 85 Honda (it seems fine, but I'm old and I don't push it).

To put the "wobble" in perspective, my 1948 Norton ES-2/Interstate is solid as a rock. No surprise there, eh?

Rod

 

[TurbineGen]

That's just part of the restoration process... improving the handling. The problem is my business is classic bikes. I don't build show pieces with incredible clear coat paints and excessive chrome. These are built to be ridden and look stock. I think it is something in the forks (probably not thick enough) causing them to flex that is causing the speed wobble, but I know nothing about the mechanics involved. I'm an electrical guy.

I have an '83 GL650 SilverWing that is rock solid all the way through 115, which is where it tops out. It never wobbles, but it has a fork brace, 37mm tubes and about 200 less pounds than the 4 cylinders I'm having issues with.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[LadaTrouble]

I noticed this happening when lower profile tyres came out,and also tyre pressures went up.I think they have too wide a contact patch,and this upsets the handling.My featherbed Norton developed a high speed oscillation using modern Michelin tyres (in 1980),by changing the rear tyre to the old Avon Roadrunner it went away.Same with my 1971 XS650 - I went back to the old profiles and stopped the shake.

 

[BrianPetersen]

A lot of those older bikes had flexible frames (as viewed from modern standards). I know the Superbikes of that era needed extensive frame bracing and some folks were using TWO steering dampers. They generally have crap suspension front and rear, too. Changing the fork oil just restores it to its original crap condition.

If the steering head bearings and wheel bearings and swingarm bearings are good, and the frame and swingarm don't have any cracks, and there is decent damping in the suspension at both ends, and the tires are good, and the engine mounts aren't loose, it's probably as good as it's going to get without doing aftermarket modifications.

 

[evelrod]

Those early 70 era Japanese bikes all had major handling problems on the street. Kawasaki/Suzuki had a couple of really bad two strokes that led to a less than stellar reputation while Honda and Yamaha put out "British replicas" that were better than Kawa, but really poor copies of Norton/Triumph. The reason as I see it that Kawa came back with the Z-1 and late 70's bikes that were superb in handling was their crash attempt at getting their market share back. Honda/Yamaha/Suzuki were soon to catch on and came out with bikes that handled well in the early 80's.

When y'all talk about "old bikes" I see 1930's and 1940' bikes...Can't seem to get my head around "old" as being 1970's...I've got boots that are older than that!

Rod

 

[swall]

One aspect of tire sizing is how it effects both rake and trail. More of both=better stability. Unless you actually measure the tire height, the stated tire sizing can be misleading, especially with the wider, lower profile tires.
I put Dunlop K-81's on my '75 BMW R90S when I wore out the OEM Metzlers. Front Dunlop was a 3.60x19 vs the OEM 3.25x19. Bike had a high speed wobble after that, due to the Dunlop being a low profile tire, which was not as tall as OEM. Once I figured that out and went back to stock tire sizing, this time with Continentals, the wobble went away. The BMW Airheads are noticeably short on trail and small front tires make these bikes wobble.

 

[TurbineGen]

I tried the steering dampers, they simply make the wobble less severe but it is still there. All the frames have been in good shape, but I usually strip and repaint them. I always replace the head bearings, but still have wobble issues.

I know this is a historic problem. They wobbled from the very beginning. I want to know how to help correct it or at least make it better. Aftermarket parts are an option.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[LadaTrouble]

My Airhead has 120mm,or 4.73in trail,pretty extreme by todays standard.It doesn't wobble,but don't like the small front tyre...it pushes and exits wide.A fat front tyre sorts that.

 

[evelrod]

Well, yeah. You can run the trail out to chopperesque...

It won't turn, but it won't "wobble" ether!... ;o)

Rod

 

[LadaTrouble]

Turning is what my R65 mono does best - you need a lot of front tyre to turn in hard and get the power on early.Yes,I know what you are saying - but bikes can be set up for different uses and riding styles beyond what the manufacturer intended.

 

[drwebb]

Might be worth checking frame alignment either through tedious plumb measurements with ingenious geometry or throwing one up on a computrack bench. Recall the early 80's "custom" models preceded the Japanese 'cruisers' of today, and no doubt had performance envelopes to match. I believe the MYs you cite predate six-sigma and 20th century tolerances may not be able to deliver on 21st century expectations!

 

[MALK]

try writing to the classic bike magazines published in the uk, for recommendations regarding tyre choice & pressures. From personal experience my old (but much newer than than these 70's bike) had the same problem at 100mph +. Seemed to go away when I replaced the rear spring & damper.

 

[TurbineGen]

Well, I finally figured out the problems. The forks on the classics I have been restoring are a bit undersized and they tend to flex when the wheel is turned. Adding a fork brace corrects almost all of the problems with the poor handling. They definitely turn better and don't have a speed wobble anymore. Unfortunately it doesn't look at all stock, but I guess that's a small price to pay.

I also have been using Pirelli tires almost exclusively. The Sport Demon tires combined with a good fork brace turn the old bikes into a totally different animal.

Thanks for the suggestions.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[thruthefence]

eg ill handling

"Kawasaki/Suzuki had a couple of really bad two strokes"

I have been frightened in my life, due to poor choices or circumstances.

Two klicks inside Cambodia, with a broke OH-6.

Back-Alley Bangkok,

Getting lost in New Orleans, and finding myself in the Desire street projects, at midnight.

Maneuvering out of a roadhouse bar in South Louisiana, after drunken girlfriend loudly & drunkenly critiqued the Merle Haggard cover the house band was 'performing'. (think: Blues brothers roadhouse scene, but worse)

But nothing compares to the "Mr Toad" ride on the buddy seat of a Kawasaki 750 H2 'triple', behind a drunken buddy,(fearless, even when sober) through the streets, yards,back roads, and even cemeteries, of Mansura, Louisiana, at the 'Cochon de lait' ( roughly translated, 'young suckling pig' ) or "Pig Festival", in the spring of 1971 (My Gog,just realized it's 39 years, this weekend)

This thing would do "the ton" before you could spit, and would wallow between the shoulders in doing so.

There is no sensation like the blur of a sugarcane field (foliage cuts like a razor) passing your face, about 2 feet away, first on the right, then on the left, at 100 MPH.

And no helmet in those days!

 

[swall]

Thruthefence--I think some of your adventures would make excellent fodder for Pat's Pub.

 

[evelrod]

As a "kid" I was exposed to Harleys and Indians with a couple of Cushman Eagles and a Servicycle thrown in for good measure. By high school it was AJS, Triumph, Norton, Matchless, with later ventures into Greaves, BSA and one CZ. As an adult (?) I bought a few Japanese bikes, all with differing handling characteristics (all bad?). Finally ending my "real" riding career in 1988 on an '81 Goldwing. Now I just doodle around with vintage stuff...Currently my '48 Norton when I can keep the Lucas mag working (it's in the shop as we speak). British bikes have always handled well. The Lucas electrics....that's another matter.

Bottom line, the best handling street bike I recall was probably a Norton with honorable notice to my Goldwing. As a tourer, it was absolutely tops. On the other end of the scale, that Kawa triple was only "worsted" by the Suzuki triple......"BAD" is not bad enough.

TurbineGen---Glad you have the problem under control. A while back we (my son in law and I) converted an old Harley Sportster to Honda Goldwing front forks and lengthened/widened the swing arm for a BIG change in both appearance and handling. Was not at all difficult as it turned out.

Rod

 

[thruthefence]

Not wishing to hijack the thread any more then I have, I won't elaborate on Dad's pair of Harley 45's, my sister's Highlander,my brother's 'Mustang' and our ex-Ford Dealer parts delivery Servicycle.