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Technical 396 Chevy block with blocked water passage

Discussion in 'The Hokey Ass Message Board' started by Kevin74, Jan 1, 2022.

  1. Kevin74
    Joined: Jan 1, 2022
    Posts: 4

    Kevin74

    Hey Guys,

    New member here, so probably a dumb question.
    Why do I see what appears to be blocked water passages at the front and rear deck of this 1966 396 engine block?
    Thanks,
    Kevin
     

    Attached Files:

  2. drptop70ss
    Joined: May 31, 2010
    Posts: 1,186

    drptop70ss
    Member
    from NY

    s-l1600.jpg Quick google search shows a 65-66 block in ebay that looks the same, must be normal.
     
    Deuces likes this.
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 50,967

    squirrel
    Member

    The heads and gaskets are the same on both sides, so they have a coolant passage in the head at each end....but the block only has the passage at the rear, because you want the coolant to flow all the way to the back of the block, before heading up and forward through the head.

    that's how all the Mark IV big blocks are.

    this is the 396 in my shop right now....

    deck.jpg
     
    Deuces, ekimneirbo, GordonC and 6 others like this.
  4. big duece
    Joined: Jul 28, 2008
    Posts: 6,379

    big duece
    Member
    from kansas

    I believe all the Mark IV blocks were that way...
     
    Deuces, kidcampbell71 and 427 sleeper like this.

  5. big duece
    Joined: Jul 28, 2008
    Posts: 6,379

    big duece
    Member
    from kansas

    Squirrel is always the quick draw!
     
  6. Kevin74
    Joined: Jan 1, 2022
    Posts: 4

    Kevin74

    Wow! I really appreciate the fast response; you guys are awesome.

    As a follow-up topic, this is a 3902406 block, which is supposed to be a 396, but the block is bored to 4.320, which is like 0.195 overbore for a 396, or 0.070 overbore for a 427! I didn’t know you could overbore this much.
     
  7. tomcat11
    Joined: Mar 31, 2010
    Posts: 217

    tomcat11
    Member
    from Kalifornia

    He is quick on the tree, and has the right answers! I'll just delete another post.:oops:
     
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  8. squirrel
    Joined: Sep 23, 2004
    Posts: 50,967

    squirrel
    Member

    are the freeze plugs out of it? The test to see if it'll take the larger bore (4.25 or more) is that you can't stick a normal wood #2 pencil in between the cylinders, though a freeze plug hole. On the blocks that will not take the larger bore (like my 396), you can fit a pencil through them. This is because of the thickness of the cylinder walls.
     
  9. Budget36
    Joined: Nov 29, 2014
    Posts: 8,453

    Budget36
    ALLIANCE MEMBER

    That’s some awesome knowledge right there!
     
  10. SEAAIRE354
    Joined: Sep 7, 2015
    Posts: 424

    SEAAIRE354
    Member

    It sure is. Been playing with big blocks a long time and never heard of that. Guess I’ll throw out my ultra sound.
     
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  11. squirrel
    Joined: Sep 23, 2004
    Posts: 50,967

    squirrel
    Member

    It's an old thing, I expect you can find it elsewhere on the internet. Of course you'd want to check the wall thickness with ultrasound, if you have a thin wall block that's punched out to the big bore size.
     
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  12. I like to go conservative with boring a 396. No more than .060" over for my liking. I'd rather make up for displacement with the stroke even if it means more expen$ive pistons.
     
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  13. Kevin74
    Joined: Jan 1, 2022
    Posts: 4

    Kevin74

    According to internet lore, in 65-67, Chevy used the same casting for 396 and 427, and just bored the block according to which engine was desired. These are the blocks that pass the pencil test. Supposedly, these blocks can go 125 over to a 427 bore with no problem.
    I have no personal experience; I’m just reporting what I’ve read in the past few days.:)
     
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  14. squirrel
    Joined: Sep 23, 2004
    Posts: 50,967

    squirrel
    Member

    Well...the 396 that I posted a picture of the deck surface, fails the pencil test, it has a late 1965 casting date. It's already 60 over, so I was pretty interested in checking out that internet lore you're quoting. It's BS.

    If your block is a 4 bolt main, then it might be the same as a 427 block.
     
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  15. joel
    Joined: Oct 10, 2009
    Posts: 2,122

    joel
    ALLIANCE MEMBER

    Correct me if I'm wrong ;the 65 396 bore started at 4.093 and wasn't 4.125 from the factory until late 69 and 70. I don't know why the factory started with an unusual bore dia.
     
  16. squirrel
    Joined: Sep 23, 2004
    Posts: 50,967

    squirrel
    Member

    yup, 396 till the 1970 model, then it was a 402. And they called it a 396 still, unless you were ordering parts from the aftermarket, then it was a 4bbl 400. Not to be confused with the small block 2bbl 400 :)
     
  17. Kevin74
    Joined: Jan 1, 2022
    Posts: 4

    Kevin74

    Yes, this block is 4 bolt main
     
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  18. squirrel
    Joined: Sep 23, 2004
    Posts: 50,967

    squirrel
    Member

    Do the pencil check, please let us know.
     
    bobss396, ffr1222k and Deuces like this.
  19. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 2,503

    ekimneirbo
    Member
    from Brooks Ky

    Some good quick reference info presented above. In the end you still need to do an ultrasonic test before you decide whether to bore it or not. If you have one that the pencil goes in, thats a good quick indicator, but cores shift and bores aren't always in the center of the casting due to production variations. Measure twice cut once applies here too.:D
     
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  20. I think they were more likely to be called out as a 402 when used in trucks. Had a 402 w/ a Q-jet in a 3/4 ton Suburban years ago.
     
    Last edited: Jan 2, 2022
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  21. Budget36
    Joined: Nov 29, 2014
    Posts: 8,453

    Budget36
    ALLIANCE MEMBER

    My grandfather had a ‘70 3/4 ton with “400” and I think an “8” as well on the fender badges. It was a BBC.
     
    Deuces likes this.

  22. I thought the pencil test was a check for sagging boobs. Learn something new every day!
     
  23. brigrat
    Joined: Nov 9, 2007
    Posts: 5,496

    brigrat
    Member
    from Wa.St.

    My pencil holder!
    IMG_1392.JPG
    And a '70 BBC 402 pencil check.
    IMG_1395.JPG
     
    Last edited: Jan 2, 2022
  24. Deuces
    Joined: Nov 3, 2009
    Posts: 21,964

    Deuces
    Member
    from Michigan

  25. Mine was a '72 Suburban (the last of the 3-doors!) but I don't remember it saying 400 or 402 or having any type of engine designation on the outside. But now that's been more than a few years ago . . . so . . .
    :rolleyes:
     
  26. Budget36
    Joined: Nov 29, 2014
    Posts: 8,453

    Budget36
    ALLIANCE MEMBER

    Lol. This was in the early 70’s. My Grandparents were over and a guy stopped to see my dad. We were out front and he said “I bet that’s a small block” looking at the emblem, he popped the hood and said “I’ll be darn”.
    If he hadn’t of noticed it I would never have this useless trivia in my head all these years;)
     

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