lcrken
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Google "scalloped tire wear". You'll find all sorts of pictures, mostly car tires, but they show the idea. Also called "cupped tires" or "cupping".
Ken
Commando steering shake.
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Ken
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It seems like you've been pretty thorough, which implies it's something subtle. I'll suggest that you actually replace the steering head bearings no matter how good they feel or appear. I had experience with 'false brinelling' on the steering head bearings of a non-Norton bike. They looked absolutely fine and felt good too. However, the bike picked up an unpleasant 'weave' that new bearings resolved. It wasn't the sort of violent shaking you're describing but it was a different machine with different rake and trail etc.
One other thing to consider. This started happening 'all of a sudden'. Maybe you threw a wheel weight? It sounds like getting the front wheel balanced might have helped some. You could remove the front wheel and set up a balancing stand and check the balance again. I would use solder wrapped around a spoke for your weight. This puts the weight on the centerline which is better than the usual stick-on weights on one side of the rim that shops like to use these days. I know lots of bikes handle just fine with weights stuck to the rim but it's time to do more than you've done so far. ( applaud your perseverance and thoroughness, and hope you can finally get this fixed.
One other thing to consider. This started happening 'all of a sudden'. Maybe you threw a wheel weight? It sounds like getting the front wheel balanced might have helped some. You could remove the front wheel and set up a balancing stand and check the balance again. I would use solder wrapped around a spoke for your weight. This puts the weight on the centerline which is better than the usual stick-on weights on one side of the rim that shops like to use these days. I know lots of bikes handle just fine with weights stuck to the rim but it's time to do more than you've done so far. ( applaud your perseverance and thoroughness, and hope you can finally get this fixed.
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+1 with Martyn , change the head bearing for the sealed one , cheap test .............
Probably a long-shot, but.......
Recently I put a Matchless G11 back together after a spruce-up. I rode it down the drive and the front end shook violently.
Back to the workshop and on the lift and checked everything. The front wheel spindle clamps were finger tight.
Ok, a silly oversight, but a small amount of looseness caused a violent shaking of the bars at 15 mph.
The only things I can suggest regarding your problem is the integrity of the clamp bolt in the fork leg which secures the spindle and also are the pinch bolts in the bottom yoke tightened fully. (I don't think that I've seen a mention of them in this thread.)
Recently I put a Matchless G11 back together after a spruce-up. I rode it down the drive and the front end shook violently.
Back to the workshop and on the lift and checked everything. The front wheel spindle clamps were finger tight.
Ok, a silly oversight, but a small amount of looseness caused a violent shaking of the bars at 15 mph.
The only things I can suggest regarding your problem is the integrity of the clamp bolt in the fork leg which secures the spindle and also are the pinch bolts in the bottom yoke tightened fully. (I don't think that I've seen a mention of them in this thread.)
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If you have steering shake, it can grow into a full-blown tank slapper. If that happens, a firm grip on the bars might be the wrong thing to do. Sometimes you need to let go of the bars and grab the tank to avoid getting launched. If that happens, you need to wait until the bars stop thrashing about before you grab them again or you might go straight over the front and end up on the deck.
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If your motorcycle sends you a message, do not ignore it. A problem with the steering can crash you very easily. When I ride a motorcycle, I always take not of how it feels as you brake and when you accelerate, when it is on a lean. You should not have to reverse steer to tip into corners and the bike should over-steer slightly coming out. If you have shake, stop and find the cause.
robs ss
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Even if that message is to let go of the handlebars and, to quote you, "wait until the bars stop thrashing about before you grab them again or you might go straight over the front and end up on the deck."
Hmmm? Do that or fit a damper? You pose a very difficult question - not!
Hmmm? Do that or fit a damper? You pose a very difficult question - not!
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I agree completely.
Why would you do this?
Have you checked the camber possibility?
I hope your handling issues become rear view items quickly.
Best
Lots more good leads here. Thanks All!
First, mixed tires; I just grabbed the Bridgestone off of another bike for a test. It was brand new AND it was the only thing I had that was the right size. Today I received a new Avon Roadrider II to match the newly replaced tire on the back. After mounting and balancing... No change! Or *perhaps* a small reduction in the strength of the shaking, which is encouraging. I opted for a 3.25 x 19 instead of the 100/90-19 that was on there on the assumption that a smaller, lighter tire (less mass) might reduce the problem. I only did a quick test ride but it still shakes. I *think* it helped but I'm not sure. I balanced the wheel with stick-on weights. Maybe I'll pull them and try wrapping wire on the spokes. Seems like a reach but I like that look anyway.
While I had the front wheel off to fit the new Avon, I twisted and tugged at the forks to see (again) how the head bearings feel. They still felt fine with no notchyness or play but I think I'll take the advice to replace them anyway. Having only had the bike for 6 yr., I don't know it's whole history but the bearings could well be 50 years old. The Ft. wheel bearings will get replaced too just in case.
I had neglected to say that the shaking happens under acceleration and deceleration, throttle on or off and coasting down hill, when passing through 40+- accelerating or decelerating. I can just detect the shake if I hold the bars tightly enough to open the throttle so accelerating tests are tricky.
Camber is an interesting idea. If it's different wheel to wheel, how would I correct that? Frame straightening? Swingarm? At one point I swapped the shocks Left for Right with no effect. The fork tubes ARE snug in the triple clamps and I double checked the pinch bolt and triple clamps. All was well.
I don't want to use a steering damper. While they're great in the right circumstances, I worry it would at best, mask the problem. I'd rather try to find the problem and repair it. THEN maybe I'll add a damper for extra stability. Besides, the bike never did this before in the years I've had it. I just noticed it one day a few months back.
Someone asked about the 15'/lb. torque I used for the steering head. That figure came from the old factory service manual I have, Sect. G, last page. I didn't look elsewhere for alternative figures but I'm open to suggestion. I did re-check that that was the tension I used, +- the accuracy of my wrench at least and that the spacer tube was installed.
Cliffa suggested I check the Rear axle. What should I be looking for? I have the factory original "half-axles". The "wheel axle" is true although I noticed the hex-head sweged on to the axle is a little crooked. I figured that wouldn't make any difference as long as I don't use it as a reference for wheel alignment. Am I missing something useful here?
Last, Dero mentioned checking the front brake. Again, what should I be looking for? I did notice that I can set the brake cable so that with the brake off and the wheel up in the air spinning, the brake *just* drags in one or two spots. It's like when a bicycle's caliper brake is a little too tight on a slightly out-of-true wheel. I didn't think anything of it and just loosened the cable slightly until the wheel spun without dragging. But now that you mention it, something's obviously out of place (or out of round) in the system. That said, the steering shake happens with the brake off. I haven't tested it, or notice anyway, with the brake applied.
Next week I'll buy some bearings for the head tube and front wheel and put them in., I'll report back what I find weather they help or not. Meanwhile thanks again to everyone for our help.
Best regards and stay dafe out there.
-Danny
First, mixed tires; I just grabbed the Bridgestone off of another bike for a test. It was brand new AND it was the only thing I had that was the right size. Today I received a new Avon Roadrider II to match the newly replaced tire on the back. After mounting and balancing... No change! Or *perhaps* a small reduction in the strength of the shaking, which is encouraging. I opted for a 3.25 x 19 instead of the 100/90-19 that was on there on the assumption that a smaller, lighter tire (less mass) might reduce the problem. I only did a quick test ride but it still shakes. I *think* it helped but I'm not sure. I balanced the wheel with stick-on weights. Maybe I'll pull them and try wrapping wire on the spokes. Seems like a reach but I like that look anyway.
While I had the front wheel off to fit the new Avon, I twisted and tugged at the forks to see (again) how the head bearings feel. They still felt fine with no notchyness or play but I think I'll take the advice to replace them anyway. Having only had the bike for 6 yr., I don't know it's whole history but the bearings could well be 50 years old. The Ft. wheel bearings will get replaced too just in case.
I had neglected to say that the shaking happens under acceleration and deceleration, throttle on or off and coasting down hill, when passing through 40+- accelerating or decelerating. I can just detect the shake if I hold the bars tightly enough to open the throttle so accelerating tests are tricky.
Camber is an interesting idea. If it's different wheel to wheel, how would I correct that? Frame straightening? Swingarm? At one point I swapped the shocks Left for Right with no effect. The fork tubes ARE snug in the triple clamps and I double checked the pinch bolt and triple clamps. All was well.
I don't want to use a steering damper. While they're great in the right circumstances, I worry it would at best, mask the problem. I'd rather try to find the problem and repair it. THEN maybe I'll add a damper for extra stability. Besides, the bike never did this before in the years I've had it. I just noticed it one day a few months back.
Someone asked about the 15'/lb. torque I used for the steering head. That figure came from the old factory service manual I have, Sect. G, last page. I didn't look elsewhere for alternative figures but I'm open to suggestion. I did re-check that that was the tension I used, +- the accuracy of my wrench at least and that the spacer tube was installed.
Cliffa suggested I check the Rear axle. What should I be looking for? I have the factory original "half-axles". The "wheel axle" is true although I noticed the hex-head sweged on to the axle is a little crooked. I figured that wouldn't make any difference as long as I don't use it as a reference for wheel alignment. Am I missing something useful here?
Last, Dero mentioned checking the front brake. Again, what should I be looking for? I did notice that I can set the brake cable so that with the brake off and the wheel up in the air spinning, the brake *just* drags in one or two spots. It's like when a bicycle's caliper brake is a little too tight on a slightly out-of-true wheel. I didn't think anything of it and just loosened the cable slightly until the wheel spun without dragging. But now that you mention it, something's obviously out of place (or out of round) in the system. That said, the steering shake happens with the brake off. I haven't tested it, or notice anyway, with the brake applied.
Next week I'll buy some bearings for the head tube and front wheel and put them in., I'll report back what I find weather they help or not. Meanwhile thanks again to everyone for our help.
Best regards and stay dafe out there.
-Danny
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Fast Eddie
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True, but...
True, everyone countersteers, as you say, it’s physics, if they don’t do it they don‘t corner. Period.
But, many people don’t realise they’re doing it. Once you realise, and start doing it consciously, it’s a very different experience and something to experiment with. But some people believe they’re doing something new, which of course they aren’t.
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That torque figure is for the 1971-on sealed ball bearings which have a spacer tube between the inner races so have no 'preload adjustment'.
Fast Eddie
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Danny, as LAB says, the ‘book’ torque for the steering stem nut is based on using balls and the torque is purely to clamp the inner races to the spacer tube.
When people talk about torque with taper rollers, it’s usually with regards to a preload on the bearings, these set ups require a lock nut to keep things correct. A spacer tube can be used with taper rollers, but as TW eludes to, the spacer tube with taper rollers is SUPER critical. A few thousands too long or too short and those bearings ain’t working correctly. I’m not talking theoretical fine tuning here, I’m talking NOT WORKING CORRECTLY.
Taper rollers in this application (using a spacer tube) aren‘t really an ideal set up unless you have accurate measuring tools, a lathe, and the ability and experience to do this right. Did the PO have these things? You’ll be eradicating some very strong possible causes by reverting to balls IMHO.
Its also worth remembering that taper rollers with a spacer tube have ZERO adjustability. You can only adjust for wear by shortening the spacer tube. And doing so VERY accurately. It is quite feasible that your spacer tube was a thou too long, and then wear has exacerbated this and brought on your symptoms ‘suddenly’ as the gap became sufficiently critical.
Ref the rear wheel spindle, as its a two piece design don’t get caught out thinking it’s tight just becasue one side is tight, you have to ensure both sides are tight. A loose side will induce a weave or wobble for sure.
Can you think back and recall any correlation between changes made and symptoms starting? Example: did you fit the DT head steady over winter only to find the symptoms started in spring, or similar?
Sudden onset indicates that either something has BEEN changed, or something HAS changed (ie you have changed something, or something has changed due to failure or reaching a critical wear point).
The possibility of something critical being worn or having failed would be a huge concern to me. I wouldn’t consider the bike safe until having resolved this.
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SteveA
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I read this in an earlier post!...
'Changed shock pre-load from Min. to Max. No change. Returned to original setting. (4 yr/ 2500 mi old ICONs)'
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Definitely agree. It is small and I believe it has been addressed in the past, If you only analyze with single dimension thinking you get single dimension changes.
I hold that it is a very low frequency vibration caused by a resonance of the drive train.
Specifically the energy of the rear wheel-rim-having tire lateral movement being both or either out of round or having lateral movement that has failed to be detected. The out of position mass induces thrust into the swing arm passing through the iso's, which have a clearance and allow a bit of movement through the rubbers. The transmitted energy of the rear wheel fed into the mass of the frame/bike has a natural resonance at the wheel speed at 35-40 mph.
The lay of the molded tread, the mass distribution of rubber or rim steel. All are difficult to measure seemingly small but the mass of the rotating rear wheel imbalance is profound when put into a rubber system that can be enticed to resonate .
To compound the problem is if the two wheels(F&R) go into and out of synchronization due to slightly different rolling circumference, any minor similar defects could exaggerate the wobble.
Series 1, Series 2A, and Series 2B bikes could all suffer from this syndrome but I would think to different degrees and slight different speeds from different front end castor and rubber stiffness and iso clearances,
Put any commando on the center stand,
aim the front tire forward,
Go to the rear and push the rear frame loop left and right and see what the front wheel does?
tail wagging the dog
Just a theory I have been thinking about for 20-30 years
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Indeed .. Apologies for missing that... what caught my eye in that post was the info that a much lighter friend had reported no problem which suggests a weight distribution problem ie too little over front wheel
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Commando S/As, from my experience, aren't very resistant to bending; the later gusseted ones are much better. I check all the S/As that are candidates for reassembly by securing the pivot tube in a vice such that the tube is leveled, you can then measure up or down from the axle slots to a fixed reference that is also level with the pivot tube and you should come up with the same measurement, if the S/A is askew your eye, in my experience, usually tells the tale, if askew you will have a camber issue. The S/A can be bent back, but I check the port and starboard by mounting the S/A in the cradle, mounting the chain wheel and checking the chain run; you can make minor adjustments with shims on the dummy axle, but if the S/A has a port/starboard tweak that is beyond the scope of shimming you'll see it. This too can be fixed, but with a compound injury I'd recommend getting a new or undamaged replacement.
Lastly, if the S/A demonstrates bend(s) the rest of the motorcycle needs to be checked against factory measurements. There is a post on this board where one of the members went to great lengths to make the measurements, did the corrections and was personally amazed at how much better his Commando felt.
Glad you have a matched pair of tires, and not to beat a dead horse, do they have the same speed rating?
Best.
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