Greg, considering your vast knowledge in all things Norton Commando, I am surprised you have missed the sketch in the workshop manual which clearly states the 850 and 750 frames are NOT identical.
"The 850 triple trees add 1 degree". Add to what? It's a 1 degree reduction vs. the 750 yokes. The frame rake remains at 28 degrees (62 degrees measured against ground horizontal) for an 850 frame. The net effect is a substantial increase in trail of 850 frame and 850 yokes vs. 750 frame and 750 yokes.
Fitting 750 yokes to an 850 frame reduces trail vs. the stock 850 combination, but trail will still be larger than on the 750 frame/750 yokes combination. You claim handling is similar to a stock 750. I can't verify this. Others may chime in.
Fitting 850 yokes to a 750 frame increases trail vs. the stock 750 combination, but trail will be lesser than on an 850 frame/850 yokes combination. You say this combo improves handling (against the stock combination). How so?
The factory made extensive road tests using professional test riders to determine the best combination in demanding loadcases. I doubt any of us is experienced enough to recommend the factory's design to be overridden. This throws up the question, does AN really vouch for fitting 850 yokes to genuine 750 frames? Hitherto I have considered their offering to be valid for their 1971-on replacement frames only which are all made to 850 specification.
Apart from opinions of what works and what doesn't, there is also the question of eligibility. The bike received type approval using a certain combination of parts. By fitting non-standard parts, the bike is no longer type approved. Loss of e.g., direction stability caused by fitting non-standard parts could have severe health and financial implications. Hence, jimbo, we have to be careful with statements like fitting non-standard yokes "without a problem". If anyone opts to do it, it is on his/her own risk.
- Knut
