What's terribly funny is the lack of appreciation for what "casting alloys" constituted 40+ years ago. You will never know with any degree of certainty about the metalurgical composition of these parts. Heck, it could easily have wandered slightly from batch-to-batch, model-to-model, year-to-year.
Obviously every manufacturer changes their processes and materials as time and volumes change. If the early 750K bikes were low production, then more hand time could have been spent and lesser quality alloy used. As demand increased and production numbers flourished, more stable choices for alloys would have been chosen to limit bad production runs and to reduce "handwork" for cosmetic repairs prior to shipping. Nature of manufacturing.
I personally have never seen a vintage alloy engine part (car, truck, plane motor, or motorcycle engine) that was "polished". Never. I'm not saying they didn't exist, but I've never seen one. And I have eyeballed Pebble Beach restores of some 8 figure resotration of European top flight doozies during their restoration and post. I've had extensive exposure to DuPont's restoration and collection and there has never been a polished part resembling the work reflected here. Sure, they have been blasted, vapor honed, tumbled, etc to get a decent luster, but never a high polish.
And to my recollection, Vic has never produced a polished restoration either?
Having said all that, I prefer the high polished result. But I am not interested in a Concours restoration. I prefer "better than" original because time and experience provide wisdom and choices for improvement. To each their own. Love them, pamper them, flog them, whatever. But for God's sake, ride the dogs!t out of them and enjoy them!
This and a couple of other comments kinda sums it up for me. A local friend has a CB350F he's owned since nearly new. It now has 9000 kms. on it, always stored inside and he restores vintage Hondas. His Rickman is perfect. However, I inspected his bike to determine what the original looked like. I would say the engine covers are not polished, and were likely tumbled or somewhat polished to some level, then clearcoated. Over time his clearcoat has "patina", and certainly does not look polished. My direction though is to polish to high shine level. I think it just sets the bike apart and folks will appreciate what it took to get there.
From my 30 years of automotive experience, all castings have porosity and they do take measures to minimize it. In high pressure situations, they actually inject a resin into the casting to fill the porosity... well, these don't need that, but the beadblasting has revealed a few pock marks... I would only lightly sand so far.... pock marks can be polished, and stand back 3 feet and you'll barely notice them. And if you do, you'll think that's OK. And I'm a bit OCD but accept that absolute perfection is not possible given what we're working with.
I have looked at 550's and 750's of different years.... the processes evolved, they are not necessarily the same as the CB350F.... all good. Yes, do what lets you sleep at night and it'll look great regardless.
If you look at a Yamaha FJR rear differential, you will see lines on the surface that appear to be cracks.. several have asked what to do about them. What they are is shrinkage lines as the casting cools... I can only imagine vintage Honda castings may have looked that way and needed a quick cleanup to get rid of the lines... They are actually above the surface, not below it, so if one was sanding it wouldn't take much at all to make them disappear...... Yamaha chose not to, and it's just a "normal" appearance, they are not rough and I'm guessing powdercoated. Looks OK to me..... just a thought.....
