Hanslwbar vibrations

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Yes I know Commandos are vibe free above 4k. Great but I am always stuck behind some plonkerat 50 MPH in a horrible vibration patch round 2600 to 3100 RPM which becomes painful. I have tried all sorts of wacky schemes but now made a pair of the heaviest possible bar end weights. These have shifted the bad vibration to nearer 2000 RPM which must be something to do with resonance in handlebars, but today oh joy I have done a 200 mile jaunt & no pins & needles & numb hands. Whoopee. Anyone else any experience with this sort of thing?
 
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Pins & needles

I have experienced the same pins and needles in the hands because of vibrating handlebars. Sitting in a line of crawling traffic on the way to work is never any fun . Even worse with vibrating bars. The only way i found was to go up or down a gear.
You could try a different pair of grips to cushion it a bit.
I have recently repaired my clutch so the primary and rear chain are all retensioned and the engine tuned with new capacitors at the points. I seem to have it tuned a lot better than i normally could get it. The vibration has gone from the handle bars and reappeared at the foot pegs.
Not a with pins & needles intensity just an awareness of something not there before. Oh for an open road and 4k plus on the tacho!
Hope you are able to clear it up.
David
 
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Interesting you both came up with similar issue to mine. My old Combat motor with unknown balance was smooth as silk above 4k (really turbine like) but since a rebuild 3 yrs ago with new rods & pistons & good 850 cases, there was always a coarse vibe through the pegs above 4k. This year a complete crank balance showed the timing cheek to be way out compared to the left but it has made no difference. It feels like mains but there's no rumbling. Yes I have that roughness through the bars at 2500-3000 but I put up with it.
What ISO rubbers are you guys running? Have you got Norvil headsteadies? I have std 850 top mount but put in Norvils Mk3 conversion though cannot get my head round the instruction to tighten adjuster and back off 1/2 turn before torquing main bolt to 25ft/lbs. Even allowing for thread play being taken out when compressed it seems you'd end up with a huge clearance but not so. I just checked mine and the front is about 006" but the rear I cannot get a feeler in, must be 003" or less and that will up the high speed shakes. Maybe I tightened the adjuster too much but I know I backed it off 1/2 turn. Just got back from vacation but will have a go tonight and see what difference adjusting to 006" clearance makes on the rear. Still I know when I had shims the high speed vibe was there at 006-008" so I don't expect much change.
 
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If your Isolastics are properly adjusted, there should be NO vibration anyplace outside the engine pod above 1200 rpm. That was a primary design objective for the Commando engine-mounting system. Complaints about vibration on the Atlas were the primary driving force behnd the design. I rode a 650SS regularly as my commuter while I was working at N-V. Even on that bike, headlamp bulbs would routinely fail at 5000 mile intervals, and it didn't matter whether you switched the lights on or not. The Atlas was even worse.

Within the engine pod, the vibrations can cause frothing of the fuel in the carbs, but "downstream" of the Isolastics should be vibration free. As I recall, the Isolastics were designed to allow about 0.3" orbital ocsillation in the worst vibration case.

Even on our cobbled-together first prototype, we met this goal. On a horribly mis-adjusted specimen, you'd be hard pressed to get any vibration above about 2000 rpm.

If you're getting enough vibration to cause numb fingers at road speeds, something is seriously amiss.
 
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I am running standard isos, I have tried shimming loose & tight, but I believe 6 thou is the correct clearance, I have tried up to 10 thou but vibrations do not reduce. I dont know if my engine is rougher than it should be, & I would love a standard motor that smoothed out at 1200 RPM!

My machine smooths out after 3300 approx & then is turbine smooth all the way up the range.

I had real bad vibes on bars occur 2600 to 3100 range, I have made bar end weights & these have vastly reduced the vibes at those RPM but now there is bad vibe at 2000 RPM. That is not so bad as I can run a gear to avoid this, so bike is acceptable, but I think I can make it better. Could the chap who had a smooth bike from 1200 RPM have had handlebars that resonated at a lower frequency?

In the range 2500 to 3000 there seems to be bad resonance in the frame, so I am experimenting with mounting damping weights on the downtubes just above the front isolastic mounts. I will let you know results of this. Does anyone reckon this may wverstress the frame tubes? Am I mad-- dond answer that one - I ride a Commando so I must be4 mad!
 
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I don't think you're mad :) I am sure that the things vibrate more than they used to. It can't all be down to "Traffic Calming" and Speed Restrictions. I can't believe that I always rode everywhere above 5000 rpm.

I know that there have been bad batches of bonded Isolastics (far too hard) but the ones I'm now using don't seem to be. Nevertheless, the shuddering and shaking through the bars and footrests (it seems to be about equal in my case) make the bike downright unpleasant in town, and I suspect contribute to the tendency to handlebar flutter.

It's not in the Matchless 650 league but it's not pleasant either.

I am amazed by talk of smooth at 1200 rpm, I can't ever remember better than low 2000s. If clearance is not the issue and if no components are "bridging" the gap, then presumably it is a case of frequency, but what would cause that to change?

Surely the whole point about Commando's was that the rubbers soaked up the vibes regardless of crank balance etc.

Has anyone in the US got access to a cache of NOS (20 years at least) Iso rubbers ?

Don't forget to post the results of your experiments.
 
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I'll put my two bobs worth in, i also have more vibration in the 2500 to 3000 rpm range after that it smooths out considerably, it's not excessive but it is still there and it does get a little annoying, i find that wearing a thicker pair of gloves helps to reduce the vibration through the handlebars and the vibration does become tedious in heavy traffic, i try to stick to the light traffic areas, and thanks Frank,you have given me a goal now, i will be persuing a vibration free bike from 1200 rpm onwards for the rest of my Nortonian existence.
Mike.
 
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Well I checked the clearance properly on my Norvil Mk3 ISO's and may have found my problem (coarse vibe above 4000). About three yrs ago I fitted the front and last Christmas the rear when I replaced the S/A pin, crank balance etc. Adjusted as per instructions, tighten adjuster, undo 1/2 turn, torque up. Stupidly I never measured the clearances. What I found last night is that on both front & rear I have little clearance in one position but appx 006" in opposite pos'n. Undoing each adjuster another 1/7 turn gives me about 004" to 008" between fr & rr (actually worse difference on the front).
With 1/2 turn that would have been in frame breaking country and I hope explains the high rev vibe. I could not get out but will this w/e.
What put me on to this was the 'Worlds Straightest Commando' article and talk of out of square ISO tubes. I'm sure I never had this problem with the shim setup, I know I didn't because the engine was super smooth at high revs. Could it be that the Mk3 ISO's have less tolerance to tube squareness because they are more rigid? Having the outer caps threaded to the rubber's support tube instead of floating on the through bolt with the shim design? Any ideas?
Certainly Frank's comments are interesting and since he was there when our bikes were under development you have to take that on board but since we all seem to experience those rough 2500-3000 vibes what changed? The early rubbers the bike came with in 98 were quite hard, replacements were very soft and when I went to the Mk3 they seemed to be harder. I had a 68 Fastback for 3 months in the early 70's and from what I recall it was like that but in other respects was so much better than the Triumphs I'd had I don't remember it being an issue.
 
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This has been a fascinating string. I'll admit that I don't know diddly about the later Commando series. I left N-V in June 1968 to go work for Boeing.

We put in an enormous (in proportion to total business turnover) amount of effort into getting the Isolastics just right - to the detriment of other things like that awful Italian front brake. OK, management pissed away a fair bit of money with the infamous "Green sphere" logo. I remember the comments at the Motor Cycle Show when one wag said he couldn't find the switch for the green turn signals on the tank. Another reckoned the silver overall finish, the green hemispheres instead of badges and the orange seat covers signified that the program had been funded by the Republic of Ireland Tourist Board.

My comments about vibration apply only to the very early models, up to my departure, but I'd be surprised if the primary design goal of the Isolastic engine mounting system was so badly compromised in the following few years. It was a major source of pride to the engineering folks.

We could just have gone out of business building Atlases - it would have been quicker and a whole lot less heartburn.
 
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But Frank, where would we be now without our Commandos, we certainly wouldn't be conversing over this excellent forum.
Mike.
 
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hello all, great thread here. i have just returned from 450 miles of glorious curving 2 lane following the salmon river in idaho. as i type, i still feel abit of numbness in my finger tips. my 850 seems to really smooth out after 3000 and yet after miles of holding, my throttle hand is really numb. just a quick release and shake, it is good for another stint. i thought this was just normal. does anyone know of a good thread for adjusting front and rear iso's. can you get to the rear without major removal? any suggestions on replacements, and how do you know if they need replacing. mine are stock, although the bike has sat much of its life before i got her. she doesn't sit much any more! (13,000 on the bike) cheers and happy riding.........
 
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I am glad that general experience of vibes is same as mine ie drives yer mad between 2500 and 3000. To the chap who has vibes above 4k, I think you will find them gone when you test ride you bike! At those revs mine is far smoother than any modern bike - no vibes at all. Trouble is a lot of time is spent in traffic at lower RPM. I have tried my theory of a heavy damping weight on frame downtubes just above front iso mounting and contrary to expectations it had Bu+++r all effect! Most effect has come from heavy bar end weights which has got rid of worst of low speed vibes & shifted them down rev range. I am going to increase bar end weights even more & if you are interested let you know final weight I arrive at. I have previously tried rubber mounting the entie handlebar assembly at the yokes, this works but needs very clever designing to avoid strange handling effects! Also rubber mounted turned steel lead lined hand grips- yes really - they do sort of work given very soft rubber which leads to strange feeling at the bars and setting up vibes at other frequencies just as bad. I have a bee in my bonnet about this bar vibration lark as it spoils what can be an otherwise brilliant bike. Keep ideas coming in chaps! Anyone tried damping weights on engine assembly itself?
 
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handlebar vibrations

Hi fellow shakers!,I have a set of Mick Hemming ISO adjusters on my '73 850,with a Norvil headsteady --shimmed to .006"/.008",the bike is relatively smooth at 2000pm, beyond that it vibrates quite a bit,I have not measured the F /R gaps,they were set from new at .008",I have opened up the gap as I ride trying to find the sweet spot - no joy!,what is the effect of too wide of a gap?,my 25 mile Freeway ride to work is tedious enough without being numbed by vibes -- downright harsh. Ride safely. James.
 
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James, throw away the norvil headsteady, I had one on my 750 and it transformed the bike into a Kango hammer at lower revs, I did improve it by drilling big chunks out of the rubber but I was never happy with it. I have a RGM/Dave Taylor rod headsteady with the MK3 spring and its by far the best, still get a little bit of shake between 2500 and 3000 but after that its turbine smooth up to red line. Just done a 1000 mile trip up to Scotland no numb hands here.
Regards
 

MichaelB

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Snakehips, thanks for the heads up the Dave Taylor. I am going to go with one on my next build and was looking for feedback from someone.
Thanks
 
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handlebar vibrations

Snakehips,thanks for the heads up on the Norvil headsteady,I have no info on the Dave Taylor steady,can you offer info. / photo.?,thanks again. Ride safely. James.
 
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I bought RGM head steady & it seems to have very little effect on vibration but sharpens up the steering as it allows no lateral movement of the head. I took mine off again whilst experimenting with other things but will put it back on later. Well worth getting
 
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handlebar vibrations

Hi Fellow shakers,I followed snakehips advice and ditched the Norvil headsteady,I put my original stock headsteady back on -- what a difference!!,still need some fine tuning of the Mick Hemming micro adjusters, but vibes. are way down,tingle in the footrests at 2800rpm,smoothing at 3400rpm.Thanks to all for advice and input.Ride safely. James
 
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James, glad its improved. The norvil headsteady's main problem I think is the rubber is so big and hard it transmits the vibes straight into the top tube, ok for racers maybe but I thought it ruined the bike. The standard set up is not bad but the Taylor unit is definately the best, mines the same as the link Lucky posted although the picture shows it without the spring which you do really need unless you have a mark3 and then you already have it. Other big plus with this unit is there is so much more room under the tank for wiring and cables.
regards
 
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