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piston size question

Discussion in 'The Garage' started by georgiared84, Jun 28, 2003.

  1. georgiared84

    georgiared84 1/2 ton status

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    I got a box of new 350 parts this weekend from a garage sale. New connecting rods, pistons and rings. The guy had taken them out of the package and couldn't remember if they were for standard, 10, 20, or 30 over. He did say that he knew the rings and pistons go together. Anyone know where they might be marked, or what the measurement is on a new piston for 10 20 or 30 over?
    Thanks
     
  2. SUBFAN

    SUBFAN 1/2 ton status

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    4.010, 4.020, 4.030 stock 350 bore is 4.00.
     
  3. HarryH3

    HarryH3 1 ton status Author

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    Those are the bore sizes, but the actual pistons would be smaller, so they'll fit into the bore. /forums/images/graemlins/wink.gif The sizes will also be different depending on if they're cast or forged pistons. Forged pistons expand more when hot, so they require larger piston-to-bore clearances.
     
  4. SUBFAN

    SUBFAN 1/2 ton status

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    Forgot, my bad.... There are no numbers at all on them????
     
  5. HarryH3

    HarryH3 1 ton status Author

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    I had started typing the same thing a while ago, then remembered that the pistons have to be able to slide up and down the bores... /forums/images/graemlins/wink.gif
     
  6. georgiared84

    georgiared84 1/2 ton status

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    I can't find any on the top, and I thought most oversized pistons were stamped on the top. on the inside are the following markings:
    a capital A inside a circle, the letters INDBRAS, P-1505,M19, and the number 69 in a circle
     
  7. SUBFAN

    SUBFAN 1/2 ton status

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    Call a machine shop those no.'s will mean something to them....
     
  8. georgiared84

    georgiared84 1/2 ton status

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    OK, feeling stupid. Put on my glasses and checked out the tops again. There is a little box with the number 12 above and S02 under it. I'm figuring that means .020 over? /forums/images/graemlins/blush.gif I've got to improve the lighting in my workshop.

    Got one more question. The crank in the box was the only thing that wasn't new. He said he had it checked out and the journals turned a few years ago, but once again couldn't remember what he had them turned to. The connecting rod journals all measure at about 2.079. The main journals are at about 2.428. Anyone got a book they can check those for me and tell me what undersize they are?
    (I still haven't gotten a new one since I accidentally torched mine) /forums/images/graemlins/rotfl.gif

    Oh, by the way, I picked up the box for $15 /forums/images/graemlins/grin.gif
     
  9. leadfoot067

    leadfoot067 1/2 ton status

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    rod journal diameter=2.10
    main journals=2.45
    hope this helps..
     
  10. georgiared84

    georgiared84 1/2 ton status

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    Thanks, looks like they are .020 under.
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    The two sets of pistons I've purchased in the last 5 years (Oldsmobile TRW .060" over) and .030" 350 SBC Speed-Pro pistons, were both stamped on the piston top. The .040" I pulled out of the 403 which were two years older, were also stamped on the top.

    I can't imagine anyone made pistons without the overbore size stamped into them, at least not in the last 10 years or so. (dunno if GM used pistons with stamped in overbore on them when they did it) Standard are usually unstamped. Of course you can't just guess with these kinds of things.
     
  12. georgiared84

    georgiared84 1/2 ton status

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    Yeah, I found it.(see my second to last post) Had to put on my reading glasses. They should start making those marks bigger!
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    I didn't see where you found ".020" or whatever. That was my point, all oversize pistons I've ever seen are clearly marked with the oversize, and the oversize unmber is all by itself, clearly visible.
     

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