Honestly. Don't polish an entire item. Ever. Your actually better of sandblasting the crank then polishing it. Well, with a very fine glass media, and not near any connection and/or bearing mount surface. Counter intuitive?
Pass-through from the carburetor port, teardrops and flairs from the pass-through, and counterweight scoop, should be polished. Everything else on a crank should have a slightly rough texture to it. Yes polishing increases flow-rates in some areas. But it also lowers turbulence, (Remember, we want turbulence as to get a good mixture) and smooth surfaces let droplets form much easier.
The same goes for the inside of the crank case. The transfer channels can/should be polished, anything else should not. Well, actually the areas where it should seal could in theory benefit from polishing as well but only at the cost of removing material, so leave them alone.
And the same again is true for the conrod, and the inside of the piston.
B!
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