Commando steering shake.

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To align the wheels, I use a string line with a couple of matchboxes at the rear of the rear rim ro space out the line from the front of the rear tyre. If the wheels are out of line slightly, it can affect the handling, but usually will not create a weave. If there is a twist in the frame, you have a different situation. Ss you compress the suspension the wheels move sideways in relation to each other. The bike usually becomes more difficult to turn. It would not cause a weave. A weave is probably caused by loss of suspension control, or it might be too much clearance on the frame and wheel components If you can move the rear wheel sideways by hand, you have too much clearance. It should be zero.
 
Hi All,
Checking in with a little update.

I received, mounted and balanced and installed a new REAR tire today... No difference. Still shakes it's head violently around 40 MPH (indicated). Maybe 4-8 hz. and +- 3-4" at the bar ends. Seems to be easily dampened by holding the bars snugly and it clears up above c. 45, although I haven't exceed 60 or so since it started acting up. Next I'll get a laser to dial in the alignment but with the more primitive tools at hand, it looks pretty good.

Thanks to everyone for you ideas. I'll keep you posted.

-Danny
 
GTCarlos said:
Hi All,
Checking in with a little update.

I received, mounted and balanced and installed a new REAR tire today... No difference. Still shakes it's head violently around 40 MPH (indicated). Maybe 4-8 hz. and +- 3-4" at the bar ends. Seems to be easily dampened by holding the bars snugly and it clears up above c. 45, although I haven't exceed 60 or so since it started acting up. Next I'll get a laser to dial in the alignment but with the more primitive tools at hand, it looks pretty good.

Thanks to everyone for you ideas. I'll keep you posted.

-Danny
Click to expand...
Get a new tire onto the front. Check isolastics for slop/wear. Check swingarm for slop/wear. Tear apart front forks for a rebuild. That should keep you busy.
 
Already told him that but he went ahead and did the rear tyre even though I told him it would not make a difference. He must be a teacher. They know everything. WOT.
 
I was reading Paul Dunstalls tuning notes. He said the rear brake on a Commando cannot be converted to rod operation.
 
The way this bike is handling, there is something simple that is wrong, number one I wound check very closely for a crack in the frame somewhere, I check my wheel alignment old way string line and ruler, on my ZX10 and ZZR1100 I do the same and have no problems up to 280 kph except my neck muscles can't stand up to it.
On the Combat when I got it going it had that horrible weave, but at about 70 mph in long slow corners, changed out the isolation rubbers and fitted the vernier adjustment, adjusted slightly on the tight side and no problem since.
To be doing this at such slow speed it sounds more like an alignment issue, reminds me of my first attempt at fitting a new tyre to my 1951 AJS in 1965, after fitting the wheel and not knowing what I was doing, when I got to about 35mph I had my first experience with a big tank slapper, stopped readjusted the wheel by eyesight and no more problems, was scary for a 15 year old in shorts and work boots I can tell you.
Burgs
 
I read an interview with Bob Trigg years ago. He said a singe-track vehicle (motorcycle, bicycle etc) is basically two casters; one is the trail of the front wheel and the other is the rear following the front. They can be MADE to wobble.

The majority of wobbles are caused by the front tire, Some bikes are more sensitive than others (some older Hondas are famously tire-sensitive, requiring OEM replacement fronts for stability) and newer sportbikes are so steep they practically require a steering damper. You see MotoGP bikes shaking their heads all the time. Most racers tolerate the shake to get the quick turning. New, matched, balanced tires are the best defense against headshake. If that doesn't cure it, a steering damper is in order. None of my Nortons have ever wobbled. Come to think of it, the only bike I ever had that would shake was my Kawasaki 500 triple. It was known for having "a hinge in the middle of the frame" Suspension set-up can also affect stability, but on these old crocks with their rudimentary suspenders. there's just not a lot of difference despite changing shocks, springs, suspension oil or preload.
 
acotrel said:
I was reading Paul Dunstalls tuning notes. He said the rear brake on a Commando cannot be converted to rod operation.
Click to expand...
Don't know what Paul dunstall means if he stated that!
As long as the pivot point of the foot brake lever is somewhere near the swing arm pivot and has a return spring it's fine
It could be worse,it could be a Seeley commando with the disc calliper torque arm mounted to the frame without the calliper mount being fully floating
 
Given the symptoms and circumstances this may not be germane, but should be checked even if just to be ruled out. I suggest that you check the torque on the steering head bearings, then with the front wheel off the ground, doesn't take much weight on the rear of the seat, move the bars lock to lock and feel for any binding, notching. Finally, with the front wheel still off the ground grab the bottom of both sliders and see if there is any fore and aft play. Different tires may induce different harmonics?

Best.
 
Hi All,

Just checking in with an update on my sudden-onset, head-shaking problem in my '71 Commando. No solution yet so I'm still searching...

Using your collective suggestions, common sense and the suggestions of a few others I have so far...
Replaced the isolastics with "vernier" type. Set to .010" clearance.
Replaced the rear tire. Avon Roadrider II (Same tire as before). Balanced the wheel.
Aligned the wheels (by sight).
Had both wheels trued and tightened (Factory steel, 19" rims).
Checked wheel bearings for play or rough spots - OK.
Moved the front tire (2500 mi. old AM26) 90* and re-balanced the wheel.
Replaced the front tire with a BT45. Same 100/90-19 as prior Avon. Balanced the wheel. That *seems* to have helped, maybe.
Installed a D.T. head steady (without springs).
Inspected & greased (tapered roller type) head bearings. No play or signs of wear. Re-greased and re-torques to 15'/lb.
Checked for movement of the swing arm. Moves freely. No play side to side. Added oil.
Changed fork oil. Inspected springs. - Found nothing amiss.
Changed shock pre-load from Min. to Max. No change. Returned to original setting. (4 yr/ 2500 mi old ICONs)
Inspected frame for cracks visually.
Confirmed no tight spots in chain or brakes.

Even if I didn't do the work competently, I assume that simply changing these items would cause a change if not an improvement in the shaking. None of theses steps had ANY impact on the problem which still occurs between about 38-44 MPH (indicated). Replacing the front tire seems to have lessened the severity of the shaking but I wouldn't swear to it.

I called a friend to confirm that I wasn't just now noticing something that it's always done. She had ridden the bike extensively last year and confirmed that it had been well behaved. FWIW, she's about half my weight. So it started all at once without my having (knowingly) hit a pot hole or the like.

So... to resurrect an old thread, What am I missing?

Your thoughts, insights and blind guesses appreciated as always.

-Danny
 
When does the shaking occur, accelerating, decelerating, steady throttle?

Personally I would not have mixed tyre manufacturers while you are trying to troubleshoot this issue, as it adds another element of doubt.

You have taper bearings, but where did you get the 15"/lb? that seems pretty high to me. For taper bearings I don't believe there is a set torque figure ( I may be proved wrong) but I would just tighten them until you get a nice smooth swing and no play, then lock them in position.

Have you checked the rear axle ?

General question, what is this "scalloping" mentioned several times on this thread? I've never heard the term associated with tyres before.

Cheers,

cliffa.
 
I would take a look at those steering head bearing again. I had similar problems with two other (non-Norton) bikes. One had ball bearings and just required a re-torque. The other I switched from ball bearings to tapered. I’m not sure on the specifics of the ball to taper conversion on Norton’s but I thought there was something about the spacer tube that was important. You might have to research that. FWIW I torqued my tapered to 16’/lb, the suggested range from the Yamaha gurus was 15-18’/ft, while the factory was 13’/ft on the ball bearings. Not sure if this is helpful, but I figured I’d share what I have learned.
 
Would the spacer tube still be required for a taper conversion?
 
Hi Danny,

I pressume your bike has the earlier Atlas style yokes with it being a 1971 model. My '68 bike used to get into a scary weave at anything over 75mph. I tried everything imagineable to sort it. When I replaced the taper roller headstock bearings with the later sealed bearings & spacer set up it was fine. I had tried adjusting the taper rollers from too slack to just right to too tight but it didn't help. Whilst my bike wasn't showing the same problem as yours a BMW R100RS I owned did. I had just completely rebuilt the bike & it would shake it's head violently at around 30mph if I removed one hand from the bars. It didn't do this before the rebuild. After much messing about with the taper H.S. bearings I sorted it.

Martyn.
 
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