Atlas vibration killer ?

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Given how remarkably smooth my 920 is with the JS kit I’d love to try a 650 or 750 featherbed Norton with the JS kit. He does extra lightweight kit for these that should work brilliantly in my mind.
This is something I have been thinking of, but first I'm going to try the Atlas as it is now it's back from NRP (exhausts). If it shakes my fillings out I'll try the 75% BF. If that's still no good it will be time to splash some cash!
 

texasSlick

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All of these old bikes vibrate to some degree. I divide them into two camps- 1.bikes that can be ridden at 70mph all day without really noticing the vibration. My MK3 is good for this as are the Vincent twins.
2. Bikes that are ok for an evening ride at speeds mostly under 60 mph with the odd blurry foray up to 70-75 while passing.
A lot of old British parallel twins are in category two. The owners might claim them smooth, but try putting the thing on a highway at speed for 400 miles per day for six days straight.
The truth will come thru, as will the vibes!

Glen
When I rode my Atlas transcontinental back in '66, I cruised all day at 60 - 65 mph, making 500 - 525 miles per day. I tried holding 70 one day, and found the vibes and wind load (no fairing) beat me up, and that I made no more miles in a day, due to more frequent fuel stops.

The Atlas (at least my own), can be as smooth as any British vertical twin, up to 3.5K rpm. At 4K rpm, near 70 mph, the vibes are too much for comfort.

Like Glen, I have found wheel balance has smoothed out the perceived vibes some. I have also changed the engine sprocket to 22 teeth, up by one, which increases road speed by about 3 mph at 3K rpm.

If I were a younger man, I would invest in the JS lightweight rods and pistons. I am sure that would be a pleasant experience.

Commandos may be smoother than an Atlas, but the handling of the Featherbeds is another type of joy.

Slick
 
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Yes Bendy Is
Interesting to read that those stand bolts were occasionally omitted. I have two non restored original featherbed twins, both with the stand through bolts in place. A 1961 Model 99, which is balanced to 84% and does not vibrate at all. Then a 1970 Mercury, also with 84%, and smooth like a silk stocking. Then a 1965 N15CS with its Atlas engine with Commando pistons (impossible to source the dished low comp Atlas pistons) and this does also not vibrate in that Matchless chassis.
My 1970 Commando vibrates like mad below 2500 and then easies out. But what a horrible roadholding. Bendy is the right nickname for a Commando.....
Yes Bendy is what I found in 1971 When I was going to buy a New Commando Roadster On first trail ride round the block In Doncaster, I felt that the Bike was steering from the back as well as the front end So As I got back to Cuswoths In Doncaster I told the dealer I was put off buying this Commando Because of the odd Handling
 
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Interesting to read that those stand bolts were occasionally omitted. I have two non restored original featherbed twins, both with the stand through bolts in place. A 1961 Model 99, which is balanced to 84% and does not vibrate at all. Then a 1970 Mercury, also with 84%, and smooth like a silk stocking. Then a 1965 N15CS with its Atlas engine with Commando pistons (impossible to source the dished low comp Atlas pistons) and this does also not vibrate in that Matchless chassis.
My 1970 Commando vibrates like mad below 2500 and then easies out. But what a horrible roadholding. Bendy is the right nickname for a Commando.....
I'm guessing these bikes were dynamically balanced at the 84%?
 
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On my 650, only the right side bolt was in place. I tried the bike with the bolt removed and all seemed the same. With the bolt put it back in to double check, there was no noticeable difference. I suppose I might as well leave the bolt in then. I might try adding a primary side bolt, just for fun.

Oh well, it was worth a try!

Glen
 

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