Atlas versus 650SS

worntorn said:
I wonder how much of the vibration problem attributed to the Atlas is actually a result of the fraudulent subcontractor hired by Norton to do crank balancing.
Seems when these bikes are given a good balance job, preferably dynamic, they aren't half bad.

About a month when out on a tour in the interior of BC, I met a fellow out touring on his immaculate Atlas, not a spec of oil showing anywhere. Only it wasn't quite an Atlas, it was a 650SS which had blown it's original cases apart, after which an Atlas motor was fitted.
The rider told me that it was quite a smooth runner, in fact he had ridden it from BC to Wyoming for the Norton Rally last year, about a 3,000 mile round trip.
He mentioned that Jim Comstock had done some work on the motor and the Matt at CNW had also been involved in the restoration of the bike. A third party had assembled the motor.
I have his contact info and intend to find out more when I pull my 650 apart for balancing.
I don't expect that either a 650SS or 750Atlas will ever be Commando smooth, but if they can be reasonably smooth to 70 MPH then that would be fine.

Glen
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70 mph is easy. Just gear it high enough to stay under 5000 rpm and they are sweet. The shake they have is a lot better than the massage you get from an old 450 Honda. Jim
 
Bernhard states he fitted 10.5 :1 pistons and the "vibration was much worse". I fitted the same after seizing up a piston....+.020 over bore, but I subjectively could not tell any change in vibration at speed. However, after fitting high comp pistons, if I revved the engine on the center stand, the machine would walk backwards...a free reverse gear!

worntorn' s musing about the balancing contractor may explain why my Atlas seems to be different from that of many others who report more severe shak'n. Ashman has stated in other posts, that a good balance job is the key to a smooth Featherbed. Perhaps mine is fortuitously better balanced.

I would love to have a smoother Atlas or Featherbed framed Norton. If I ever split the cases, I will be sure to send the crank, pistons and rods off to a top rated balancer.

one point that I am almost embarrassed to confess....I have 12 inch rise bars....not apes, but high enough to accentuate the vibrations. I had a 1 1/2 hour commute to school as an undergraduate, and riding bolt upright was necessary for comfort....not to mention riding transcontinental! I just have never changed them back, but perhaps if I did, the vibrations would not be an issue at all! Gol' dang....I just can't bear to cut back those cables and trim back the electricals.....would sooner split the cases.....

Slick
 
If yours doesn't vibrate much, if you ever have it apart,
you'd be better to weigh everything, to see what its secrets are ??

And check inside those handlebars.....

I had a CB450 - briefly.
It didn't so much vibrate as tingle.
Hands-and-fingers-going-to-sleep-type-tingling.
 
Before the use of accelerometers and computers came along dynamic balancing was a very time consuming job.
No Nortons were dynamically balanced and the static balancing that they got was pretty poor -especially in the later years.
The result of this is that no two Nortons are balanced just the same from the factory except by accident. Jim
 
Rohan said:
If yours doesn't vibrate much, if you ever have it apart,
you'd be better to weigh everything, to see what its secrets are ??

And check inside those handlebars.....

I had a CB450 - briefly.
It didn't so much vibrate as tingle.
Hands-and-fingers-going-to-sleep-type-tingling.
Click to expand...

I took a Black Bomber for one long trip and vowed never again. Short sprints and around town was great but after an hour at highway speed my hands and feet would be completely numb. Jim
 
texasSlick said:
Bernhard states he fitted 10.5 :1 pistons and the "vibration was much worse". I fitted the same after seizing up a piston....+.020 over bore, but I subjectively could not tell any change in vibration at speed. However, after fitting high comp pistons, if I revved the engine on the center stand, the machine would walk backwards...a free reverse gear!

worntorn' s musing about the balancing contractor may explain why my Atlas seems to be different from that of many others who report more severe shak'n. Ashman has stated in other posts, that a good balance job is the key to a smooth Featherbed. Perhaps mine is fortuitously better balanced.

I would love to have a smoother Atlas or Featherbed framed Norton. If I ever split the cases, I will be sure to send the crank, pistons and rods off to a top rated balancer.

one point that I am almost embarrassed to confess....I have 12 inch rise bars....not apes, but high enough to accentuate the vibrations. I had a 1 1/2 hour commute to school as an undergraduate, and riding bolt upright was necessary for comfort....not to mention riding transcontinental! I just have never changed them back, but perhaps if I did, the vibrations would not be an issue at all! Gol' dang....I just can't bear to cut back those cables and trim back the electricals.....would sooner split the cases.....

Slick
Click to expand...

Only 'almost' embarrassed...!?

On a serious note, bar end weights would help calm things down on bars like that.
 
texasSlick said:
Bernhard states he fitted 10.5 :1 pistons and the "vibration was much worse". I fitted the same after seizing up a piston....+.020 over bore, but I subjectively could not tell any change in vibration at speed. However, after fitting high comp pistons, if I revved the engine on the center stand, the machine would walk backwards...a free reverse gear! Slick
Click to expand...


Mine did exactly the same; I didn’t find it very amusing :( :shock:
 
Bernhard said:
Mine did exactly the same;
Click to expand...

Did anyone do anything about the Balance Factor though, and piston weights ?,
or just bolt in hicomp pistons and go....

Those original dished top pistons were fairly light ?
 
comnoz said:
Before the use of accelerometers and computers came along dynamic balancing was a very time consuming job.
No Nortons were dynamically balanced and the static balancing that they got was pretty poor -especially in the later years.
The result of this is that no two Nortons are balanced just the same from the factory except by accident. Jim
Click to expand...

When you dynamic balance a Norton crank, do you calculate what weight must be added to the big end to give the desired balance factor and bolt it on in two halves around each of the two journals before you spin the crank ? Or do you leave that stuff to the 'experts' ?
 
Allan, not sure if you are poking fun or serious with the "expert" remark.
Have you seen Jim's dynamic crank balancing machinery or looked at any of his posts or videos on the subject?

Glen
 
worntorn said:
Allan, not sure if you are poking fun or serious with the "expert" remark.
Have you seen Jim's dynamic crank balancing machinery or looked at any of his posts or videos on the subject?

Glen
Click to expand...
My question to Jim was not in jest or poking fun. A few years ago my friend was doing this, and I cannot remember if he statically balanced the shaft first then added weight to the journals, or added the weight to get perfect static balance then dynamically balanced the shaft and changed the static balance afterwards.
The only experience I've had of dynamic balancing was many years ago in Melbourne where we had an 'expert' who was not an expert. If you've got access to Jim Comstock or similar knowledge person , you are lucky. I'm very careful about giving bike stuff to car engine rebuilders to play with. It is a different game. I once had a kid in his early 20s offer to rebuild my Triumph race engine for me - I could have throttled the little bastard - I don't believe in miracles.
I haven't seen Jim's videos on balancing, have you got a link ? All I know is that I statically balanced my own crank to 72% and the motor is dangerously smooth at high revs. (Arse beats class ?) I wouldn't ride my bike without a tacho.
 
You sure wouldn't be changing the static balance after getting the dynamic balance done.
That would be undoing all the good work ??
 
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