Vibration from 2500 to 3000 rpm

My 850 joggled the engine around, a lot, at lower rpm.
But unless you put your knee against the (hot) engine, you couldn't feel it.

I did buy and fit new iso rubbers and shimmed them when I got it though - not a new bike.
Not many miles, but the rubber bits were past their best.

rick in seattle said:

Mike,

I use CRG mirrors. The internal clamp piece is 7/8"; just chuck it and clamp the mirrors directly to the handlebars right at the end of the bars. You'll need 1/2" of bare bar to clamp. The weights then mount behind the mirrors using their internal clamping piece and provide some additional security to the mirrors. I'd provide some clear photos, but at the moment my Commando is on Mercer Island and my ass is in Austin (ass and bike will reunite in May). Found an old photo, however, where you can make out the arrangement.

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Are those Yamaha Special bend handlebars?

Commandos, and Nortons for a long while before, had the option of "Western Bars".
Don't know if those are though.

My project 850 came with a set on it, could measure if needed.
The straight bit for the twistgrip etc is a neat 11" straight.

I'm in Concours camp and well know those T140 bars as they were the best there was to fit Ms Peel wide far out scope of operation excesses so comfy and secure and streamlined or peg standing as I liked long as I liked. I've regrown 2" since then so now 6'3" and back to 34" inseams instead of 32" till age 55. You might be surprised how high ya cafine bar chaser bars are compared to these T140's which are pulled back and down not out and up like ape hangers. On next ride out put your head down far as can racer style and feel the frontal area pushed, then put hands at ear level ....

For the already nerve injured vibration sensitized, think Brunwick Green, aka Brit racing green and Robin Hood technology brought up to date. But which bars or tubes to put them to best use?





http://www.lancasterarchery.com/bow-acc ... mpers.html

Concours,

Thanks for asking. When I rebuilt the Mk3, I fitted aftermarket buckhorn bars from British Cycle Supply on both this bike and my Victor. They give me a few extra inches of height and pullback. They do give a very non-standard look to the bike, but at my age they save my wrists and lower back, and allow me to enjoy this wonderful bike for a few more years. It's just like sitting in my favorate chair, but with a 70 mph windblast. Heaven.

Can you quickly run a tape measure over these bars then - they look mighty close to the Norton-option 'western bars' that were available on new Norton bikes.

Western bars measure 11-8-8-8-11 inches from tip to tip, just quickly measuring each major length.
Clutch, throttle and brake cables all came in factory lengths to suit.

Rick, how do the standard 'Export' cables work with that Buckhorn handle bar? I could see it might be more comfortable if you lower the rear of the bar so your arms come parallel off the bars?

Dave
69S

rick in seattle said:

Concours,

Thanks for asking. When I rebuilt the Mk3, I fitted aftermarket buckhorn bars from British Cycle Supply on both this bike and my Victor. They give me a few extra inches of height and pullback. They do give a very non-standard look to the bike, but at my age they save my wrists and lower back, and allow me to enjoy this wonderful bike for a few more years. It's just like sitting in my favorate chair, but with a 70 mph windblast. Heaven.

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Comfort is king in my garage. No false racing pretense here :mrgreen:

I found that removing the larger buffers in the rear iso and replacing them with extra bushes cut the vibration below 3000RPM in half. It seems that when I did this the engine/cradle vibrates below 3000RPM that it rotates around the rear iso while the range of motion at the front iso is about the same as stock, but it 'feels' much more civilized at the lower RPM's. It still goes smooth as before above 3000RPM.

Rohan,

I'll happily measure the bars when I return to Mercer Island in May.

Dave,

I checked my rebuild spreadsheet and found that I used Hi-Riser cables and hydraulic lines from OB. They are a bit longer than needed, but better that than pinched cables and lines. They work well and I don't object to the look, but you can judge yourself from the photo. I now operate the choke on my Mik from a lever on the bars; the cable is of standard length since the lever is mounted toward the center of the bars.

Lets open this up this little.

Am I being led to believe that a perfectly balanced Norton motor will run as smooth on one cylinder as two? Which then begs the question that one cylinder, left or right, at the combustion stroke, while the other is running unopposed with the valves open will produce no perceivable, or "actual" for that matter, lateral momentum what so ever?

How would you define this 'lateral momentum' of yours, thats not in my textbook of vehicle dynamics behaviour ?

"we demand rigourously defined paths of uncertainty"


Lets wander down the garden path a little - possibly not in the direction ye seek ?

If you hit the kill switch while you are motoring along at speed, and the motor is still in gear and turning over, does the engine get any smoother - or rougher. Nope, not really, it just keeps turning over.. It may emit a sonic boom when the ignition comes back on again, but that is another diversion.

If you are accelerating up a steep hill, and your mate beside you hooks his boot under your plug lead and pulls it clean off, and your Commando then runs on only one cylinder, it will feel like a POS, in no uncertain terms...

What does that tell us. ?
P.S. What was it you were asking again ??

Perhaps we can add to this a little in the meantime though.

If one cylinder goes awol, for any reason, the resulltant performance running on just one cylinder is woeful - the drag of the non-running cylinder will slow you to a near crawl or less at the sight of a hill. Its the pumping losses in the dead cylinder that kills the go.

If however, you removed the rockers in the dead cylinder, so it can neither breathe in nor out, one cylinder on its own will run quite smoothly and happily.
Not a lot of power out of a 375cc single, it must be said though, there is more friction than a single likes....

I know of someone who killed a cylinder in their Vincent twin.
Rode it back home, 1000 miles, with one cylinder suitably disabled.
He always quipped it was not much different to a 500cc comet. (the single cylinder version of Vincent).

hth

Cutting spark for dead engine drag slightly smoothes up the vibe sense, mostly what's coming from tire pulse and isolastics bouncing back off tire contact.
The harder you air up the smoother the isolastics get but the harsher the road felt, sheeze.

There is somewhat detectable horizontal imbalance if loosing a jug firing, but its more felts as the lack of thrust and slightly more jerky power thrusts than engine vibes getting through. When on Ohio trip and Wes '71 fouling plugs and loosing Boyer charge voltage I had to switch Peels plugs and took off w/o a HT lead on and got to full highway speed as fast as I desired on one lung till I noticed rough sounding and lack of spunk on throttle. I did not notice engine vibes as the clue.

By far horizontal imbalance comes from mass imbalances not combustion hits or lack there of.

hobot said:

C I did not notice engine vibes as the clue.

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gee - I've had a V8 lose a plug lead, and I stopped to see if the motor was still bolted to the engine mounts - from the vibes of the misfire it felt like it was coming loose.
It was rubber mounted though.....

After I got mine running in '10, a couple of times one of the plug wires kept falling off about 3 miles from home. I would ride it home and didn't notice much more in the vibration dept, but it did feel like a big single and was hard to keep going at low speeds.

Dave
69S

Yes I've plenty of V8's dropping a cylinder for instant obvious roughness Chevy to Fords d/t fouled plugs or HT shorts and other more serious stuff, but I could not tell on my Combats with hyw noise and semi timid throttle use leaving the stop. Try it and see. I've lost a jug d/t coil terminal slipped off for rough running but not much extra vibe except not at hi rpm, to reach under to check to get both a brust of smooth running and a sharp shock off nicked HT lead.

The most dramatic imbalanced combustion event was when Trixie blew a inferior foil-flame ring at 60's mph, but mostly the sudden blasting noises altered me and and intened to just finish trip to work in a depressed mood, but after 30 sec or so - for some reason I reflected on posts asking about fuel line heating between carb and engine routing - YIKES, pulled over just in nick of time before flames cut hose all the way through >>> El Flamo Brit Iron BBQ.

To really feel the differences of running or just spinning engine get on a good long steep and snick N and kill engine to just coast like a bicycle. Until you have felt the transformation of tri-links and extra cushions in rear and beveled away front ones , you will think you Cdo is pretty smooth rolling w/o power connected, so did I, once upon a time.