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Crank Balancing

Engine Issues

  1. money pit

    money pit Well-Known Member

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    I have a 1974 360 I'm having rebuilt. I heard the 360 is externally balanced by the torque converter. If this is true, will balancing the crankshaft affect the way the engine runs (cause vibration). Do I have my facts right? Thanks
     
  2. Adam

    Adam Well-Known Member

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    The 360 takes a special balancer and usually a torque converter with a weight welded on to it. Alternately you can use a flex plate with a section removed...

    In either case your engine balancer (machinist) should have, and use, all the components of the rotating assembly to balance the crank. This includes the pistons, rods, balancer, and t-converter, or flex plate. He may not mount these items, but does need their weight.
     
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  3. money pit

    money pit Well-Known Member

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    Thank you for the thorough response.
     
  4. David DiMartino

    David DiMartino Member

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    Going through the similar thing with 73 340 to change from automatic to tremec 5 speed. Totally agree with Adam's response. My machinist also wanted one set of rings to include in the weight calculation.
     
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  5. Mopar_EasternNC

    Mopar_EasternNC New Member

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    Interestingly, we just went a few rounds with this issue with Eagle Specialty Products as ordered from Summit Racing.

    We ordered what is advertised (at least as far back as 2012 and currently) as an "externally balanced" ESP crankshaft from Summit for a 1972 360. Machinist got it ready to go on the balancing machine and called to say "you got an internally balanced shaft."

    Numerous Customer Service communications with both Summit and Eagle taught us that Eagle claims "externally balanced" was a misprint and that they have NEVER sold an externally balanced crank for the 360.

    I personally found that hard to believe, but had no choice but to take them at their word. Thus we started moving toward converting this engine to internally balanced rotating assembly.

    As I am now having another, separate crankshaft issue with the Eagle/Summit pairing, I may have to source the crank for this engine elsewhere. If there is as source of a cast, externally balanced crank, I'm open to suggestions.

    My point is watch what you are getting when ordering parts.
     
  6. money pit

    money pit Well-Known Member

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    I had the machine shop balance the crank. One of the older machinist informed the younger machinist that you need a weighted flex plate when you balance the 360 crank. Luckily the old timer intervened or my crank would be out of balance.
     
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  7. Adam

    Adam Well-Known Member

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    I believe Mopar sells the 360 cranks, 3.58 and stroker too.
     
  8. David DiMartino

    David DiMartino Member

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    I ended up having to buy a new crank for my 340. The previous rebuild, prior to my ownership, tried to convert to internal balance and forever screwed up the crank. I found similar issues as all aftermarket cranks I found, that didn't cost 800 bucks or more, were internal balanced. I got into discussion with machinist and his balancing specialist and determined we could get everything to work the internal balance crank and other external balance components I had purchased. End result, crank is balanced to within .04 oz-inch. Damn nearly good enough for pro stock racing.
     
  9. Cojohnso

    Cojohnso Active Member

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    And of big blocks? I have a B-block 400 with a 440 crank. I know it was balanced and had to cut the counter weights down to balance for short deck motor use. (Poor man's stroker.) But I don't believe the flex plate has any weight added? Or consideration to the crank balance?
     
  10. money pit

    money pit Well-Known Member

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    I believe the 360 is the only engine that is externally balanced. Why? I don't know.I
     
  11. Cojohnso

    Cojohnso Active Member

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    Interesting. I'm willing to bet its a factory money thing?
     
  12. Adam

    Adam Well-Known Member

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    I don’t think that is correct. Weren’t late 340s, and 400 big blocks, externally balanced?
     
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  13. money pit

    money pit Well-Known Member

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    You're right. I looked it up online. The last year of the 340 cast cranks were externally balanced. Not sure about the 400 big block.
     
  14. aussiemark

    aussiemark Well-Known Member

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    Late 440 cast crank engines were also externally balanced. You can subtract weight from the counter weights on the crank easily by just drilling them to remove the required weight but it is difficult to add weight to the crank counter weights you need to use Mallory metal a very expensive heavy metal this is put in a hole and welded in place but you need the hole if it isn't there you need to drill it which also removes weight so the whole process becomes a head ache. I am building a 340 engine with much lighter pistons and con rods then the original parts and want to reuse the original crank (forged std size journals) but it may be cheaper to upgrade to a new 4340 crank then to have the original balanced to suit the new parts.
     
  15. aussiemark

    aussiemark Well-Known Member

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  16. Cojohnso

    Cojohnso Active Member

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