Fixing the speed wobble problems
Fixing the speed wobble problems
(OP)
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.
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.
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
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.
RE: Fixing the speed wobble problems
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
RE: Fixing the speed wobble problems
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.
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
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.
RE: Fixing the speed wobble problems
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
RE: Fixing the speed wobble problems
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.
RE: Fixing the speed wobble problems
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.
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
It won't turn, but it won't "wobble" ether!... ;o)
Rod
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
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.
RE: Fixing the speed wobble problems
"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!
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
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
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
Of course, this is coming from a guy who is contemplating removing his center stands from three bikes to acheive a greater lean angle... I keep smakcing mine off the ground in turns and it scares the life out of me. I know old bikes weren't meant to handle like that, but then again, if they can be modified, then why not?
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
Anyway, it seems many of my bikes liked one particular brand or another and would handle poorly with any other make. The old Yammer 650 would only do well on Michelin while the Beezer only liked Metzler. My KZ liked Dunlop but my GL1100 would only take the old Goodyear "run flat" tubeless. Those Goodyears really were 'run flat' as I made it home a couple times with nails in the rears. As long as I stayed under about 35, no harm-no foul. Too bad they quit selling them. Don't know why, they had good grip, they did not scare the crap outta me in the wet, they would do 6000 to 8000 on the rear...and...they were fairly cheap. They did have one drawback...a real bugger to mount an dismount. Oh well, that was ancient history.
Rod
RE: Fixing the speed wobble problems
RE: Fixing the speed wobble problems
I have race take-off Dunlop Sportmax GPA Ntecs on it now, and they work fantastic on the back roads, but they're not going to last long.
Michelin Pilot Power has worked well on this bike in the past and I have a new set ready to go on.