Buffed pistons
 

Hi,

If you know how to create shine on somehting you will try to apply it to anything.

Last weekend was inspecting my stock pistons any I found them to be rough on the top. I got myself some 400 sanding paper and tried to work my way down to 1500 grit wet standing.

Here are some pictures;


The tops now all have a mirror like finnish to them.

I didnt feel confortable by removing more material to level all the casting dimpels, there are some left.

This does not have big potential other that "some" safeguard to detonation, thats all I think.

Please discuss :)

Make sure you reweigh and rebalance them after removing material like that.

Yes thanks, will measure and report :)

At the risk of sounding stupid, can this cause different engine characteristics like lower compression? Obviously probably negligible.

Negligible

is it really more than a dust that comes off with a 1500 g cleaning? What is the weight tolerance difference between them that becomes a problem?

Yeah that’s a fair point. I’ve heard you want them within ~.5g of each other but I’m not sure at what point it’s an issue, for a mass produced motor I’m guessing 1-2g would have passed spec for the OEMs

Technically, you are reducing compression ratio a teeny bit too. Smoother surface doesn't dissipate heat as well as rough surface. Smoother surface reduces tendency for hot spots to form which helps raise det threshold (a good thing).

1.1g max deviation

thats a lot.

Curiosity was killing me so I pulled out my extra box of Supertech 83.5’s and weighed them with my trusty eBay scales. Mine were a whole lot worse than what you started with before lots and lots of cleaning and polishing.

Cleaned up they now weigh 444.2, 444.2, 444.1, 444.0 with pins. The pins were each 100.8. Are stock ones really that much lighter or does the +0.5 make that much difference?

EDIT: my son says he doesn’t think they are Supertech pistons.

Unless you're using the same scale I wouldn't pay the most attention to the actual numbers. Calibration can be way off from one another. I see yours has been calibrated somewhat recently, unclear what OP is using.

If a digital scale that reads out to tenths of grams is off by 50 grams that's not just calibration.

FWIW, out of the box my Supertechs (84mm) were 289.3, 289.6, 289.6, and 289.9, with the wrist pins being 98.7, 98.2, 98.0, and 97.7. Paired up that way the assemblies were within 0.3 grams of each other, right around 388 grams.

--Ian

Yes, I am aware that a 60g variance isn’t due to calibration, thank you.

I was simply pointing out that it might not be as big as a 60g difference based on calibration.