Atlas versus 650SS

In the very likely event that I cannot find a suitable 650SS here in the "States, in the opinion of the learned group how much " real " difference is there between the Atlas and the 650SS ... other than mere preference?. I have heard that the 750 cc motor is very " buzzy " ... without benefit of Isolastic's ala Commando models. I have owned two Commando models .... 750 and 850 ...liked them both.
Thank you for input and guidance.

Jim.

The first Atlas models to arrive in Australia had a problem - the barrel flanges pulled off. I think on the next model the problem was fixed. My impression is that the twin carb 650cc Manxman was a much better bike. It depends what you want, bigger is not necessarily better. I believe that Norton's problems started when they enlarged the 650cc twin. The Manxman was as far as they could logically go with the rigidly mounted motor and the featherbed frame. It's pretty obvious that if you live in the land of freeways a bigger motor is more atttactive. It was all about the CB750 Honda. My own motor is a Mk2A 850 and it is great, however it is always a worry, and I think I could get a 650SS going just as quick however more reliably. Our problem with bikes lies in perceptions. When I was a kid and old bike dealer said to me that he didn't know why anyone needed a bike bigger than 500cc. I think we don't really value some things for what they are. I'd love to own a twin carb 650SS - much better than any Triumph.

Could Always build a ' Atlas SS ' .

the ancient pistons are the 2 piece over 6000 ones ( 750 - Split skirt , or it splits over 6000 )

HOWEVER , if your not a puritanical pedantist over ' originality ' a custom injun with commando
top end could get it humming along nicely . then theres the getting it stopping nicely . :twisted:

Then the COLOUR of the TANK is Different , usually . :shock:

I can not speak of 650 ss, as I have never owned or ridden one. I have owned a 62 Atlas and now have a 63 Atlas (I am original owner).

I was told before buying the 62, "don't do it...Nortons shake too much!" I am sure the sages giving that advice were using the 650 as their guide, as the 62 Atlas was too new in the US to have any reputation or history. Those giving me advice at the time were 650 BSA and Bonneville guys, and I had ridden both their bikes.

I could not pass up the 62 Atlas, as it had only 1800 miles on it if I can remember rightly, at least too few to matter much. it was like new, with a discount.

The first thing I noticed was it did not vibrate any worse than the BSA or Triumph of my friends.
Next thing, was it could barely beat them in the zero to ton event. Frankly, I was disappointed in the performance; the "buzz" factor was a non issue, but I hardly was an expert in that arena.

I jumped on buying the 63 as it advertised 60 hp vs 52 for the 62. The 63 went like one would expect with 100 more cc's over the 650 Beezers and Trumpets...the 63 was crisp, the 62 was flat. I did not perceive any more shak'n going on, but the 63 was definitely less tractable than the 62. I found I had to drop down to third gear under 35 mph, but the 62 would tolerate 25 mph in fourth.

I rode the 63 transcontinental...grueling! The buzz was definitely there at a steady 70 mph, the mirrors useless, but the grueling part was not so much the vibes, but holding on against the wind with no fairing or backrest. I found that fuel economy went into the toilet at 70, and had to stop more frequently (only had a 2 1/2 gal tank) for fuel. At the end of the day, because of more fuel stops, I was no further down the road at steady 70, than I was cruising at 60, where the vibes were not unduly mindful.

Read Ashman's posts re: 850 engine rigid in a Featherbed frame....he says the combination can be made smooth enough for 80 to 90 mph cruising. Ashman has given me the incentive to go with JS Eng lightweight pistons and rods, which are said (Jim Schmidt) to smooth out the 750 Atlas.

I love the Featherbed frame of an Atlas or 650 ss, I used to say in my youth "if I rode anything else, I would probably kill myself"

Keep us informed as to how you go.

Slick

Having ridden both 650ss (mine) and a well set up Atlas, my choice would be for a 650ss. However....the likelihood is that a nice project 650ss will be a bit hard to find, an Atlas will probably be a bit easier to find. Going for either increases your chances by 100%. A "standard" 650ss will be faster, smoother, sweeter than an Atlas in my opinion.
If I was doing your search today and looking for a project road bike, with no great concerns about originality, I would aim for either. Then put a decent disc set up on the front and if it is an Atlas, build the motor to Commando spec, but get the crank balanced i.a.w. the hints on this forum.

Both great bikes, probably the best of the era, with the 650ss certainly better than any Triumph from the same time.
Best of luck
cheers
wakeup

The Norton 650SS is listed in Guinness World records as the world's fastest production motorcycle from 1962-1967. The Vincent Black Shadow from a decade earlier was faster, but it was no longer in production.

Glen

The 650SS is a sweet revvy little motor. They lack the midrange torque of a 750 but make up for it up higher.

The 750 Atlas is sweet if you don't try to raise the compression or rev it high. Stick some high compression pistons in it and a cam and they are not so sweet on the street -not for long rides anyway. Jim

worntorn said:

The Norton 650SS is listed in Guinness World records as the world's fastest production motorcycle from 1962-1967.

Click to expand...

Thats an interesting claim.
Which makes you think for a while.

An Enfield Constellation 700cc, with 51bhp and a GP carb no less, from the late 1950s would have given it a run for its money ?
And the Cycle World test of March 1963 got an average of 119 mph from an Atlas.
And the best quoted for the 650SS was 118 mph.

Are the official speeds quoted anywhere ?

Not that top speeds are terribly relevant these days....

comnoz said:

The 650SS is a sweet revvy little motor. They lack the midrange torque of a 750 but make up for it up higher.

Click to expand...

If you sleeved an Atlas down to be a 650SS, would it go better ??

Rohan said:

comnoz said:

The 650SS is a sweet revvy little motor. They lack the midrange torque of a 750 but make up for it up higher.

Click to expand...

If you sleeved an Atlas down to be a 650SS, would it go better ??

Click to expand...

Can't say I have done it but theoretically if you copied the 650s bore, compression ratio, reciprocating weight and balance factor it should act like a 650ss. Jim

The centreline of the bore does not pass through the centreline of the crankshaft on the 750 and up Norton twins. This probably increases the vibration.

I cannot speak of 650SS, as I have never owned or ridden one. I have owned a 65 Atlas and with the standard 7.5:1 pistons the vibration was acceptable. But me, being a bit of a racer, I went and fitted 10.5:1 pistons and twin carbs. The vibration was then much worse.
Doug Helne at the time advised that the 750 Atlas should be sold with the low compression pistons because of the vibration bugbear. I did not know this at the time.
Also, the Atlas engine is inclined towards the rear, but I have seen rigidly mounted Commando engines inclined forwards in a f/bed frame.

Rohan said:

worntorn said:

The Norton 650SS is listed in Guinness World records as the world's fastest production motorcycle from 1962-1967.

Click to expand...

Thats an interesting claim.
Which makes you think for a while.

An Enfield Constellation 700cc, with 51bhp and a GP carb no less, from the late 1950s would have given it a run for its money ?
And the Cycle World test of March 1963 got an average of 119 mph from an Atlas.
And the best quoted for the 650SS was 118 mph.

Are the official speeds quoted anywhere ?

Not that top speeds are terribly relevant these days....

Click to expand...

A friend who owns a Constellation also disputed the Guinness record. I had no answer for him, then remembered seeing video of the 1962 and 1963 Thruxton Production TT where the Norton flew by Connie's, Bonneville, Bsa 650s and everything else in the race.
If repeatedly winning the Thruxton 500 mile Production race doesn't qualify a machine as "World's Fastest Production Motorcycle", then I suppose nothing does!

Glen

Interesting comment that the vertical centrelines of the crank and cylinder bores are different on 750/850 motors , I thought that the motors were, for all intents and purposes, the same spec., except for bore size ?.

Jim.

johntickle said:

The centreline of the bore does not pass through the centreline of the crankshaft on the 750 and up Norton twins. This probably increases the vibration.

Click to expand...

DeSaxe and reverse DeSaxe engines have been discussed for almost as long as combustion engines have been around.
Can't automatically assume anything ??
Interesting comment though.

[quote="Limeyrider"I thought that the motors were, for all intents and purposes, the same spec., except for bore size ?.
[/quote]

The headgasket for a dommie 500 will almost fit an Atlas 750, and vice versa, except that the bores have been moved, looks like about 1/4".
About everything else is different sizes and placements, but all extremely similar.

There is a small difference in cylinder -main bearing alinement but I suspect it was done to make a big motor easy without changing as much tooling.

I have done some experimenting with moving the cylinder center on a 750 race motor. The only difference I could ever see was that there was a little more cold piston noise when I centered the cylinders over the crank. I did not do back to back dyno runs but I did not see anything real different in power or vibration and didn't pursue it any further. Jim

comnoz said:

There is a small difference in cylinder -main bearing alinement but I suspect it was done to make a big motor easy without changing as much tooling.

Click to expand...

Yes - the cam and followers and drive have a near fixed relationship to the front of the cylinder,
so it was expedient to just move the cylinder back, rather than try to move the cam etc forward...

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

Its maybe worth commenting that somewhere along the way, Royal Enfield twins were seen to have vibration problems,
after which it was decided to give ALL their twin cranks a dynamic balance.
Didn't entirely solve everything, but they were oft noted as quite smooth when road tested.
And there were no Friday or Monday bikes....

Its amazing that Nortons didn't twig to this contractors methods,
if thats in fact what was going on. ??