Thank for your reply.
(1) I checked the wheel spacers and front wheel spindle all OK.
(2) I had a visual examination of the frame, it seems OK. But in what area would I expect to find damage?
(3) Honda man's comments below on CB750 wheels suggests they are built wrong!
Maybe this is the answer to the problem?
Honda man writes this:-
Here's the whole story of how "Jimbo" Jim Chamberlain and I first "discovered" the front wheel offset phenomenon, the related head shake, and the fix:
Jim had a K0 sandcast bike, one of the very first in Central Illinois. He wanted a dual-disc setup, like he saw at Daytona in 1970. But alas, his early K0 only had the mounts for a disc on the left side fork. The K1 had just come out in 1970 with forks that could fit 2 discs (specifically so Honda could use them at Daytona), if you made your own right-hand triangle mount (all you needed was the lefthand one and some washers and a file to make one). This was all happening just as I had started working with him in the Peoria shop, Brown's Sport Center Honda. A friend of his came in to buy a 750, and Jim talked him out of the dual-fork setups, paying the guy an undisclosed amount of cash, then swapping the front ends between the bikes. Upon his first test drive, Jim noticed the new headshake phenomenon, pronounced because his front tire was also somewhat worn, as he had promised the other guy would still get his new tire and had dutifully swapped tires, too. So, the following weekend, as a test, Jim put a new tire on his: the headshake remained. When his friend's bike came in for the 500 mile maintenance, Jim talked him into a "swap-back" test: suddenly Jim's K0 had the old forks and wheel back (with a new tire from the newere bike) and the wobble disappeared. Jim wanted the 2-disc setup badly enough that he swapped it all back to the original agreement, and the K1 owner rode off, never knowing how much better his bike handled than most K1 bikes.
In the swapping process, we did notice the wheel rim was closer to the fork on the disc side, though. So, a few weeks later, Jim retrued the wheel over to the middle, guessing it at 4mm difference, using the fender's center as "reference". The headshake disappered instantly. This posed a different problem, though, when his 2nd disc arrived: the reversed caliper had alignment problems, hitting the disc at an angle, and scraping the rim sometimes. So, he offset the wheel back the other way about 2mm ("split the difference") and filed away the offending corner of the caliper. In the end, he swapped the forks around and ran the calipers behind the fork legs to reduce the heavier feeling that the extra caliper adds to the steering when it is "up front". In our last discussion on the topic, he believed that one day, when it wasn't college finals season, he was going to realign the rim back over to center, to see if he could get away with it in the corrected location and with reversed calipers. It was about then that I moved to Macomb, and I never talked with him again, except by a couple of letters, regarding transistorized ignitions like the ones I build now: that was THEIR beginning, circa 1972.
So, like I told McRider: it's a long story, but true, and out in plain sight: if you can find a sandcast bike's owner with the asymmetric forks, we could maybe find out the distances between the wheel rim and the inside of the forks, both sides, and compare that to the later bikes. You'll probably find them to be off about 3mm or so, toward the disc side, on the later bikes, and more even on the early ones. Be sure to discuss wheel bearing slop with the K0 owner (i.e., make sure there isn't any) and and make sure the fender is not used for reference here, as most of them get bent and twisted with fork activity over the years, so they are not centered any more. Try to find a good way to masure it: that's often hard for the novice who wants to use a ruler instead of long-head calipers or transfer verniers. I have not yet met a K0 owner here at SOHC4 who is also "machinist" enough to have the tools needed to make the measurements.
