Hi Texan, I have very strong opinion this, as well as real life personal experience. Environmentally it's a wash. So forget that .
Real life, the original as cast finish is impossible to replicate. Period. We can only do what gives closest or original.
Vapor honing (blasting) is very fine media mixed with water. The media must be removed. It looks very similar to soda blasting. Some people feel it looks closer to factory. I'd say a wash. Both look very good.
Soda blasting is a form of baking soda with a graded grit & a non clumping additive. Very hard deposits will take a lot of time. It is MUCH more gentle on surface than any other dry media I've seen. Way better that bead blasting. Very hot water & brush works well in cleaning off media. I'm not saying soda actually really dissolves, but it cleans off well & fairly easily.
With the above methods if you take an aluminum polish such as Mothers or the like on coarse cloth using plenty of compound, go over the surface & "polish" it to a small degree. This brings out the gloss original casting has to a good degree. Experiment how much to polish on bottom of motor/trans until you get the feel for it. Buff with coarse cloth followed by smoother cloth like terry cloth towel.
Bead blasting, even with fairly fine clean beads is the worst way in my mind. It completely changes the surface of the alloy. It can never really look original again. You can make it look much, much better by polishing like above, but takes much more polishing to look closer to original.
Want to insure you need to heilicoil or timesert spark plug threads? Bead blast them!! 95% will need threads sooner rather than later. It also ruins the gasket seat for plug seal. Don't screw yourself!! Take spark plug. Break off porcelain & screw into hole, grease on threads & tighen. Then clean by chosen method. Clean every last bolt hole with tap & compressed air. Again bead blasting is harder on every single thread in motor.
Supposedly the polishing compounds contain some form of bee's wax or the like which reduces oxidization of cleaned parts. I don't really know of any kind of coating that helps. I know most oil will turn yellow. Every clear coat I've ever seen peels or turns yellow. I just leave them.
Again I most, most strongly recommend do not bead blast. If you have large enough compressor you can buy soda blast kit & do at home. Soda will kill plants & grass. I learned that the hard way. I used plastic canvas. But the soda goes everywhere. Blast cabinet works fair. Even the best soda likes to clump. It takes a lot of soda to do entire motor.
Head, cly, is my bike. Blue Tiger. Bead blasted, polished head. Rocker boxes, rest of motor is original. Notice how sand blasting changes color of aluminum. I should have soda blasted it afterwards, then polished. I was so discouraged, I just said screw it & put head on. Oh yes, plug threads were blasted too. Had a hard time removing them. Don't bead blast is my recommendation.
Notice how head is more white silver than the rocker boxes & case. Bead blasting will always do that.
There is also dry ice blasting. I've never seen it.
Don
