Hoofhearted said:
I don't want to hijack a thread and turn it into a pissin match.
You did , and you are wrong.....
When you say "the engine is not a stressed member", then you are saying that none of the stress the chassis sees in it's intended use is channeled through the engine/transmission unit. That is, it could be suspended by rubber bands or springs and not affect the handling or performance of the chassis at all, which is dead wrong.
The Norton featherbed as designed had it's head steady attached to the top of the engine, and it's engine/transmission bolted rigidly in place exactly because stresses from the normal use of the chassis were transferred through it.
If all Norton wanted to do was to contest straight-line speed trials with it's motorcycles, then it never would have needed the Featherbed frame at all, it could have gone on using the primitive rigid or garden-gate plunger frame. But Norton was involved in World Championship Grand Prix road-racing, which as everyone knows involves closed circuits with combinations of stresses from turns, braking ,acceleration and uneven road surfaces.
For their road racing machines, the Manx, and the street bikes they sold with the Featherbed frame, they incorporated the parts necessary to brace the steering head to the engine of the machine.
Just because here and there over decades oddball private owners leave pieces of the frame off or modify it for other uses means nothing at all...