427 Tall Deck Balancing
+ Reply to Thread
Results 1 to 7 of 7

Thread:
427 Tall Deck Balancing

  1. #1
    Member FishWagon's Avatar
    Join Date
    Apr 2010
    Posts
    32

    Default 427 Tall Deck Balancing

    Hello all,

    I'm starting my build of a 496. Due to finding a great deal on a block, I have gone with a 427 Tall Deck block.

    It can hold a 4.375 crank without a problem, but I'll stay with a 4.25 stroke.

    I am going to source a 4.25 crank, 6.8 rods, and 1.27 pistons.

    1.27"piston pin height, + 6.8" rod length + 1/2 of 4.25" stroke(thats 2.125") equals 10.195" or .005 below the 10.2" deck on a tall deck block
    thats a 1.6:1 rod/stroke ratio.

    My question is that from my research, I can internally or externally balance this engine.

    What are the pro's and con's of the balancing methods?

    Thanks,
    Rich

  2. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  3. #2
    Senior Member
    Join Date
    Dec 2007
    Location
    concord, ca
    Posts
    913

    Default 427 tall deck

    Internal balance. Makes swapping parts a breeze. And its the way most people are going. External is only if those are the parts your starting with.

    I have the same combo. Currently two engines. Both 427 tall deck with 4.25 stroke. One naturally aspirated with nitrious, and one with twin turbo's. Good setups.

    Jerry

  4. #3
    Senior Member
    Join Date
    Jan 2009
    Posts
    428

    Default

    One depending on which year 427 t/d block you have you may (may) run into little to a lot of grinding at the bottom of the cyl bore near the cam side to get the rods to clear the bottom of the bore. again some will clear and some not. your going to need to mock up the block and check each one.

    Also your going to want to get the block square decked as your going to find those blocks deck specs are all over the place.

    These are a good thick casting and .060 is no problem i have done a few at .125 over and one even went .140 over

    I feel line hone is a must along with main studs these blocks were made for about 2800 rpm redline in the old trucks so specs and clearances were pretty general.
    it's up to you on lifter bores have them checked but if it were mine i would bush them.dont assume there are not egg shaped or wore out.
    I always put a reher-morrison upper lug kit in the intake valley if your going to run real high compression or nos

    I would internally balance the motor and should be pretty straight forward with that long of a rod and compact piston ht your going with, if there is a uprade on piston pin i would go that route.

    Just putting some things out there that i have found running this block myself for a long time, hope it helps and best of luck

  5. #4
    Member FishWagon's Avatar
    Join Date
    Apr 2010
    Posts
    32

    Default

    Excellent, thank you.....

    Block/heads/intake are at the machinists we speak. The block was never used for a running motor. It was found in a crate, and subsequently sold to me for $250 after being checked by a machinist. Block was in excellent condition, with some VERY minor surface rust in the cylinders. It was very well preserved by whoever packaged it.

    The block is stamped "marine" as well, as is already notched.

    Thanks...

    Rich

  6. #5
    Senior Member wizbang's Avatar
    Join Date
    Feb 2008
    Location
    Kent, WA
    Posts
    1,293

    Default

    Quote Originally Posted by FishWagon View Post
    Excellent, thank you.....

    Block/heads/intake are at the machinists we speak. The block was never used for a running motor. It was found in a crate, and subsequently sold to me for $250 after being checked by a machinist. Block was in excellent condition, with some VERY minor surface rust in the cylinders. It was very well preserved by whoever packaged it.

    The block is stamped "marine" as well, as is already notched.

    Thanks...

    Rich
    So this block is "new" never run ?

    It's funny , we have done lots of these factory Chevy blocks. Machined them after lots of miles. What we see is not very good machining from the factory ? Or is it that when they originally machined them, they were
    " green " and after the engines have been run and heated up and cooled off so many times, seems the castings move and take shape. So what we are seeing really is not that the original tolerances are all over the place, but that the block takes a set after being run, now they need to be machined to get them to the right specs ?

    We just did one that the main caps were not flat on the mating surfaces nor were they 90 degrees to the block surface. It took .008 off the caps to get the line hone to come back to .ooo ???????

    When we decked the block, the deck was like close side to side, maybe .002 or so, and front to back was that close also. But talk about a lumpy deck surface. It was within .002 of being square, but took .011 to get it flat ?

    What do you think ?

    After we run one that we machined, the things look great.

    ( Sorry, I'm noit trying to hi-jack the thread, just curious about a new block if that is what this thread is aboiut ?)

  7. #6
    gn7
    gn7 is offline
    Senior Member gn7's Avatar
    Join Date
    Jan 2008
    Posts
    25,876

    Default

    I don't know if you have one, but GM ran off a boat load of tall decks before they shut down the line. Chet Herbert moved a ton of these as did a guy I know out of Pheonix. My understanding is a guy out Las Vegas bought a thousand of them from GM, and part them out to different vendors. I bought 2 of these. $250.00 is a damn good price. They are They can be ID pretty easy by two means. First, everything behind the flywhell is flush with the bell housing mounting flange. The cam bore, lifter galleries, etc. Like they were all made with the same cut. They were. You'll know if you go to but restrictors in and need to use the ones for a bow tie. Otherwise they will hit your mounting plate behind the flywheel. The other is, it will swallow a 4.250 crank and the biggest rods you can find and then some. With the right rods, 4.375 will go, with no grinding. Truck blocks just seem to have the worse tolerance of all BBC. Its not so much a green thing and they move a bunch after running. They are machined wack at GM. Maybe it was the low po thing. Don't know. But new ones I had were the worse. Line bore was OK, but not good, decks off by a ton, front to back, in opposite directions. Ended up taking off .020 to get there. Bore where all over the place. It was as if GM was just jambing them thru the door. They knew they weren't going to be building motors with them. Good luck on your build. thats a nice find
    LINK:GN-RACING.COM

    "there are too many pigs for the teats"
    Abraham Lincoln

  8. #7
    Member FishWagon's Avatar
    Join Date
    Apr 2010
    Posts
    32

    Default

    Yeah, I'll know more from my buddy once he looks it over. He's going to check everything. There is not so much as a scratch anywhere on the block, it looks completly virgin.

    Anyway, internal balance it is, talking to my buddy, he said the same thing, internal balance is the way to go.....

    Thanks all, I'll let you know about the block once Rob checks it out and runs it through his shop. Rob mentioned that years ago before aftermarket blocks were popular, these blocks were in high demand due to their ability to be seriously stroked compared to standard deck blocks.

    Anyway, thanks again.

    Rich

+ Reply to Thread

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.
If you do not want to register, fill this field only and the name will be used as user name for your post.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.


Digg This Thread

Posting Permissions

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
  •  

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91