Any one knows how to stop an Atlas vibrating? (Apart from buying a Commando)
I have read in the Commando site that one Atlas owner lightened the pistons- I went the other route by working on the crankshaft, to no avail.

Hi, obviously they vibrated from the start........but it could be worse now , with heaviest "commando" pistons (not concave), and bad headsteady.........you could try to dynamically balanced it (had done it to 84%, for three bikes ), and on my own Atlas ( with GPM "commando" pistons )it was better , specially after 3000 miles (ish...), have it geared high ,with a belt drive, and at 4500 / 80mph, it was nice.
My next Seeley had the JS therapy...........!

I find that if I just turn it off the vibration stops.

Having a magneto with symmetric timing probably helps ?

There's no fix for it. Rigidly mounted engine with two big pistons going up and down together vibrates. What was marginally acceptable on the 600cc Dominator series got less so on the 650SS and much less so on the Atlas. It was pretty bad on other big twins, too. The Royal Enfield Interceptor comes to mind.

The prime driving force behind the Commando design was to isolate the engine vibration from the rest of the bike. Story was that a headlight bulb on the Atlas only lasted 5000 miles, regardless of whether it was ever turned on. The vibration made the bulb element fall off the terminal posts.

Spung saddles were popular once .
Farmer told me hed got his new , riden it down to Singapore , I think , across Aus . Sold it after a year or two in NZ as to remote from to remote an agent for serviceing . Had the spares Wanted 150
for a few chains and odds and ends . A HARD man / Said ' The Bars vibrate at 90 . put your hads to sleep . You have to hang on Tight . Down through Italy etc , though nothing fell off sitting on 90 for a few hours
a few times , sat on 80 mostly thru Europe .
NOW .
theres a " Vibration Phase " they all do it . So you balace it , percentage , to get it where you arnt . Due to frame harmonics , engine plates , bolts , resonances , its immpossible to calculate how to get it SMOOTH .
So you figure what rpms you want it ROUGH , say 2000 or 2500 , and say you want its Vibration Phase THERE . Thats Easy . THEN itll be smoother at all other revs .

Ignition setting and carburation can ' phase ' too . Best things MANUAL ADVANCE , pulled back puttering & " I stuck it right forward , the tyre smoked takeing off Dunno if it was the Uncle with the Alloy 500 Fb & twin , but fairly common with youngh upstarts , and olderones if a car tried haveing them , back 1970