I got this reply from 'Hondaman' (Mark Paris) on the SOHC4 site
Re: Markings on early CB750 cranks - FOUND THE MARKINGS
« Reply #7 on: Today at 10:09:05 am »
The notches are unusual! I don't remember seeing those. Huh
With the lots-of-touch assembly that was done to the sandcast bikes, it would not surprise me to find out that they were matching rods to positions on the crank: a big (sales) deal was being made of how smooth the bikes were at the time (like they needed any more help to sell them...). As wrenches, we were flogged to balance the carbs every time a K0 stood still in our shop. Those 4 cables sure were a nuisance for that particular feature!
The "Q" codes you've found are much like the numbers that got stamped into the matched caps on the Rocker Towers: they indicate parts that have been matched in machining. Starting in the K1 series, or maybe during the early diecast engines, the weight codes became spread over the split in the rod caps so the extra match-markings were not needed, eliminating a step in production.
The "7" you found is an early weight code: they are usually "5", "6" or "7" so they don't get confused with the bearing/journal numbers of "1", "2", "3" / "A", "B", "C". Most of those came and went, mostly 'went' in the K5 and later engines. K3 lost them for a while, too, as I remember. And, they are hard to see! As the cranks got better in casting, the rods were used to offset the variances in the flyweights instead of trying to match the weights. This is one big reason why the engines after K2 were not as smooth as the legendary "old factory" K0/K1 engines. If you don't have the markings on the crankshaft, it's not very simple to balance the rod weights with the crank!
ByranJ: there were Katakana characters on the very early crankshafts (and rod weight codes), and in a few other places, too. They became "normal" characters pretty quickly for exported bikes, though. I have seen the pictographics on bikes that were bought in Japan, too!
