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Piston Material

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  • Piston Material

    After honing my block yesterday, I noticed a strange black mark. It was only at the top of the piston. And after asking around could only be identified as something that got caught between the piston and the wall.

    My question is this, obviously I'm going to loose some compression, but does this little mark make it an unsuitable engine to drive daily with some beating now and then?

    Also, it has Arias pistons, which I'm told is some 2118 material, something along those lines, I can't remember. (someone else chime in?) And was told it expands. A lot. Now I could probably hone this mark away, but would take more than 5 thousandths I'm guessing. But this man also said that this material can expand somewhere near 10.

  • #2
    Is the mark on the cylinder at the top of the piston at TDC or at the top ring? If the mark is above the top edge of the top compression ring then it won't affect compression.

    Forged pistons do expand more than cast but I would not exceed the manufacturer's guidelines for clearance in your application. You'll end up with piston slap and blow-by. It's been a while since I looked it up but I believe modern hypereutectic cast pistons call for a clearance around .0005" and forged pistons around .0015". If the Arias pistons were already in there, the gap is probably already setup for forged pistons.
    Don Johnson (really!)
    Just so you know.


    • #3
      Pics would make this really easy

      Those clearance numbers sound like they are per inch of bore diameter (ie 4x.0005=.002 clearance for a 4" bore)


      • #4
        At TDC it would probably reach the oil scrapper. I may be able to take a picture. It's a very peculiar thing. It is 2618 material, not 2118. I couldn't remember right. Well the guy I had look at it has been building race engines for 25 years. He actually used to build every porsche rolex engine. However, honing it away until it is gone, although that's what he would do, is not textbook. So, although he says he's seen that material expand almost 10 thousandths, it's still risky I suppose. I'm thinking of daily driving this thing, with obviously some beating, I'm just wondering if leaving it there and accepting a little compression loss will ruin everything for me or if I should re-sleeve it or what.