tinkering with pistons

simon

simon

Famous Member
When polishing piston tops, how far do I have to go?
just remove the machined lines? mirror shine?

How big may a scratch in the surface be before it could possibly become a hot spot or have a notch effect when subect to combustion pressure?

255top_small.jpg


Also, I've grown accustomed to removing every burr and smoothing every sharp edge within my reach. the areas (arrows) were less than perfect on these hypereutectiv KB-silvolite replacement pistons. Is it safe to smooth those edges?

arrows.jpg


Also, is the criss-cross shaded area where I may grind and remove material to match weight? What else can be done to make those low-buck slugs as tough as possible?

I'm not planning on any nitrous oxide, super- or turbocharging; just high compression somewhere in the neighborhood of 10:1, maybe a little less...
 
I think the criss-crossed weave area may actually be a sort of a half arsed "ribbing" for strength. I've always thought the area under the piston pins (when held upright) was the area to grind and match weight.

But I'm just guessing.. Haven't gotten that far in my builds yet.

*edit - I've always been told that mirror shine is the best.
 
8) the biggest thing is breaking up the sharp edges on the tops of the pistons. remember that any polish level you put on the top of the piston will be gone the first time you fire the engine up.

on the pin bosses you can indeed remove the sharp edges with no problem.

as for balancing the pistons, the machinist takes material from the bottom of the pin bosses to balance the pistons.

do not remove material from the cross hatch are as that will weaken the top of the piston. remember that you are right under the combustion chamber at that point.
 
The closer you get to a mirror finish on the piston top, the flatter it would look under a microscope, thus less surface area exposed, thus slower heat transfer. Since the heat transfer out of the piston is unchanged, the piston should run a little cooler. At least this was the assumption when I raced (methanol-fueled) boats, and I believe this has been an accepted notion in motor racing since the Thirties.
 
for the effort (if you ahve a buffer) a mirror shine on a surface flat like that isn't much work (block it out with some wet/dry and a quick buff on a wheel)
 
Then its gonna be mirror shine. Compared to the time I've spent to weight-match, polish and shot-peen all of the rocker arms (:shock:) this'll be easy.

Thanks a lot, I'll keep you posted. :wink:
 
I believe the cross-hatched area on the bottom of the piston is to retain splash oil (more than a smooth surface) for rod/pin lube?
 
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