The explanations show why 360-degree partallel twins vibrate so badly and why N-V tried to emulate the car industry by putting the engine on flexible mounts. Having ridden a 500 BSA twin as a yougster, then the various works "hacks" when I was working at N-V, I was best satisfied with the 650SS that I was allowed to use as my ride-to-work.
I found the Atlas and the P-11 to have far too rough a vibration signature and declined to have either one to replace the SS, which, if the odometer was to be believed, had 135,000 miles on it when I started riding it. The vibration level was acceptable by the pre-Commando standards, and having a 45-mile drive to work through Warwickshire country lanes from Kenilworth to Wolverhapton was a real bonus. I often wished we hadn't moved closer to the factory!
When we were breaking in a new P-1, before starting tests on it in response to the California dirt rider lawsuit, I hated having to drive the damn thing. It could easliy delaminte your kidneys in 100 miles, not to mention the directional instability issue.
I was riding the early break-in, limiting speed to <60 mph. It was boring until the speed got into the mid-50's. Around 45 mph, the bike started to wander - just a couple of feet side to side on about a 1/4 mile wavelength. By 60 mph, it was getting uncomfortable - using up almost the full width of a motorway lane on about the same wavelength. No amount of body English or steering input could keep it under control. The other test rider, who got a higher maximum speed limit (90 mph) after I'd done the break-in miles, said that the wandering died down above 80 mph.
Because of the vibration, bits were alway falling off. On one trip, I lost the entire rear-light assembly. The attachment bolts vibrated loose and the whole thing fell off. IMO, the Atlas and the P-11 were Norton's two worst machines. I include the Jubilee, Electra and Navigator in that list!
