Drilling Small Block Oil Drain-back Holes in Valley Area?

Small Block Mopar Engine

  1. dibbons

    dibbons FABO Gold Member FABO Gold Member

    Messages:
    4,480
    Likes Received:
    2594
    Joined:
    Nov 6, 2009
    Location:
    La Paz, B.C.S., Mexico
    Local Time:
    2:55 AM
    I just remembered today having drilled a series of drain-back holes in the '65 273 block that I ran in my bracket racer. They would have been placed between each pair of lifters in that little spot where a small amount of oil tends to sit and puddle. I also had painted the interior of the block with Rust-Oleum rusty metal red primer after the mods.

    Now, I painted up the 340 block I am preparing (see photo), but this time I am going to forego the drain back holes. That was a little scary back in the '70's, I always wondered if I was weakening the center structure of the block (the holes were not very large).

    I don't believe I thought of the idea of drilling the holes on my own, I must have read about it somewhere back then in the 1970's. Has anyone found a reference book or article that discusses this procedure? Anyone have photos of a block modified in this manner? I was just curious what was out there. Thank you.

    340 block painted.JPG
     
  2. krazykuda

    krazykuda Well-Known Member FABO Gold Member How-To Section Editor

    Messages:
    55,998
    Likes Received:
    21445
    Joined:
    Aug 20, 2007
    Location:
    Orland Park, IL
    Local Time:
    4:55 AM

    Why not just open up the standard drain back holes in the china valley with a die grinder, that's what I do to help the oil drain easier...
     
  3. dibbons

    dibbons FABO Gold Member FABO Gold Member

    Messages:
    4,480
    Likes Received:
    2594
    Joined:
    Nov 6, 2009
    Location:
    La Paz, B.C.S., Mexico
    Local Time:
    2:55 AM
    That does not address the areas that I treated back then.
     
  4. abdywgn

    abdywgn dismantler

    Messages:
    1,544
    Likes Received:
    801
    Joined:
    Jul 30, 2006
    Location:
    Darien, Illinois
    Local Time:
    4:55 AM
    I believe I had done that type of drilling because that's what was said to be done. Wisdom now says to block holes and drain at very back or timing cover area so the oil does not fall onto the spinning assembly and rope power or froth the oil. To the best of my knowledge and remembering what I've read. And blocking the opening in the middle was good for 25hp? according to one Mopar magazine article.
     
  5. dibbons

    dibbons FABO Gold Member FABO Gold Member

    Messages:
    4,480
    Likes Received:
    2594
    Joined:
    Nov 6, 2009
    Location:
    La Paz, B.C.S., Mexico
    Local Time:
    2:55 AM
    I have no plans on any more grinding/drilling on this build, just curious historically speaking who/what/where this idea was sourced from back in the day.
     
  6. moper

    moper FABO Gold Member FABO Gold Member

    Messages:
    15,767
    Likes Received:
    1885
    Joined:
    Dec 27, 2004
    Location:
    eastern CT
    Local Time:
    10:55 AM
    I add them. In big blocks too.
     
  7. RustyRatRod

    RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

    Messages:
    65,845
    Likes Received:
    39169
    Joined:
    Jun 7, 2010
    Location:
    Georgia
    Local Time:
    5:55 AM
    You don't think the oil pooling around the lifter bores aids in cooling them do you? It just seems like an insignificant amount of oil to worry about to me...at least worrying about returning to the pan. How much do you think pools there? An ounce? Maybe two?
     
    • Like Like x 1
    • dibbons

      dibbons FABO Gold Member FABO Gold Member

      Messages:
      4,480
      Likes Received:
      2594
      Joined:
      Nov 6, 2009
      Location:
      La Paz, B.C.S., Mexico
      Local Time:
      2:55 AM
      Point well-taken RRR, back when I was an inexperienced young buck, I followed along with most of the "tricks" I would read about in car publications and technical bulletins.
       
    • Jadaharabi

      Jadaharabi FABO Gold Member FABO Gold Member

      Messages:
      7,878
      Likes Received:
      8675
      Joined:
      Jan 8, 2016
      Location:
      Peoria, Illinois
      Local Time:
      4:55 AM
      Personally I grind that casting flash out of those holes in the middle of the lifter Valley. All that flash in there is just good for causing a crack.

      Had a 273 that cracked from that flashing. Ruined a good block.
      But that's just me and my personal opinion which I highly value.
       
      • Like Like x 1
      1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
        By continuing to use this site, you are consenting to our use of cookies.