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SBC harmonic balancer question

Discussion in 'The Hokey Ass Message Board' started by 1929Essex, Jan 23, 2011.

  1. 1929Essex
    Joined: Jun 5, 2010
    Posts: 83

    1929Essex
    Member

    OK I have a 350 small block in my rod now out of a '79 truck. I'm trying to save some space between the radiator and motor. I would like to know I can change the harmonic balancer to a smaller one that I have off a 283 small block. The balancer on the 283 is about a 1/4 of the size in thickness. I've gotten two opinions on it and was told it will work because the motor is internally balanced. Has anyone done this or know if it will work? The 283 motor is from a 70's, maybe like 60's nova.
     
  2. newsomtravis
    Joined: Jun 1, 2009
    Posts: 562

    newsomtravis
    Member
    from pville, ca

    usually won`t be a problem, there are a few aftermarket ones for the 350 that are very thin like the one you want to use, so, i don`t think thickness is really an issue....
     
  3. bbtom30
    Joined: Jan 10, 2007
    Posts: 155

    bbtom30
    Member
    from so. cal

    Yes it will absolutely work.We do it all the time to put 350s in early chevelles.You have to,or get to use the short water pump then
     
  4. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,474

    landseaandair
    Member
    from phoenix

    The balancers will interchange but will still have the same final length. All the difference in thickness only happens on the backside. If you don't already have a short water pump, you can gain space with it and matching pulleys.
     

  5. Shaggy
    Joined: Mar 6, 2003
    Posts: 5,207

    Shaggy
    Member
    from Sultan, WA

    Yup...
     
  6. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,484

    Johnny Gee
    Member
    from Downey, Ca

  7. Watch out for the timing marks on the balancer. The early and late Chevs balancers had TDC marked at different spot. You will need to buy a "timing tab" bracket for the older balancer (it bolts on using two timing cover bolts).


    When mixing and matching, it would be best to verify TDC and then use the appropriate timing tab.
     
  8. squirrel
    Joined: Sep 23, 2004
    Posts: 49,876

    squirrel
    Member

    I wonder why chevy went to the expense of adding all that metal to the torsional damper when the increased the stroke of the crankshaft to 3.48"?

    Must be a good reason...they didn't make things more costly if they didn't have to.
     
  9. chop32
    Joined: Oct 13, 2002
    Posts: 1,077

    chop32
    Member

    Ive always been told not to put an early (small dia.) balancer on a larger displacement engine if you plan to rev it.
    Probably wont hurt on an engine thats babied, but not a good idea if you plan to flog the snot out of it.
    Like Squirrel said, balancer diameters increased with displacement for a reason. When the power output of some engines increased, the balancer diameter also increased.
     
  10. inc4203
    Joined: Jan 24, 2011
    Posts: 1

    inc4203
    Member
    from Buffalo

    This is due to the increased harmonic vibrations. Increasing the size of the damper increases the inertia. The more inertia the better the ability to dampen. Now of course there are high end limits as well. Obviously you cant stick a 500 # damper on the crank. :D
     
  11. fab32
    Joined: May 14, 2002
    Posts: 13,985

    fab32
    Member Emeritus

    If you remember they added a larger balancer when the '64 365hp (and 375FI which was the same engine just adding the fuel injection) came out. This was to dampen a harmonic vibration that occurred above 6,000 rpm which this engine easily reached even in production form. Harmonic vibrations occur at multiples of the lowest harmonic i.e. a harmonic vibration that occurs at 2,000rpm will occur again at 4,000 and once again at 8,000. or in the case of the 327 at 3,000 (approx.) and again around 6,000.
    In drag racing you pass through the rpm ranges so fast that it doesn't matter if you have a more massive balancer (thus you see the use of smaller mass balancers on high RPM drag engines) but in oval track and road course (this also includes street driving) you can spend longer periods at smaller rpm ranges and a harmonic vibration will tear an engine apart if left unchecked for too long.

    Frank
     
  12. squirrel
    Joined: Sep 23, 2004
    Posts: 49,876

    squirrel
    Member

    Thanks for the insight Frank. Chevy put the bigger dampers on all the 350s, street motors included. I wonder why they did that? Could it be related to the switch to cast crankshafts at the same time? or that combined with the longer stroke? Did they expect all their 350 engines to eventually be used in race cars?
     
  13. unkledaddy
    Joined: Jul 21, 2006
    Posts: 2,865

    unkledaddy
    Member

    Don't forget to leave enough space for a fan.


    Aren't all 350's internally balanced? The damper in your case is just a mounting suface for the crank pulley, so any internal balance damper should work.
     
    Last edited: Jan 24, 2011
  14. squirrel
    Joined: Sep 23, 2004
    Posts: 49,876

    squirrel
    Member

    400 was the only sbc in 1979 that was not internally balanced.

    Crankshaft and bearing life is a separate question.
     
  15. Roothawg
    Joined: Mar 14, 2001
    Posts: 21,991

    Roothawg
    Member

    I just run 265's and 283's, that way I don't have to worry about the dampner size. :)
     
  16. 26 roadster
    Joined: Apr 21, 2008
    Posts: 2,017

    26 roadster
    Member

    I use the smallest lightest balancers on my race motors (circle track) and spin 68-7200+.
    They are all well balanced though
     
  17. chop32
    Joined: Oct 13, 2002
    Posts: 1,077

    chop32
    Member

     
  18. bulletproof1
    Joined: Feb 23, 2004
    Posts: 2,080

    bulletproof1
    Member
    from tulsa okla

    glad this came up...is one pump better than the other? as in short over long..other than room....
     
  19. 1929Essex
    Joined: Jun 5, 2010
    Posts: 83

    1929Essex
    Member

    thanks for all the input, the main reason I wanted to go with the smaller dampner and short water pump was to have enough room for an electric fan.
     
  20. BBYBMR
    Joined: Apr 27, 2007
    Posts: 613

    BBYBMR
    Member

    Aren't all 350's internally balanced? The damper in your case is just a mounting suface for the crank pulley, so any internal balance damper should work.

    BINGO. That's why, if you use a 350 block and aftermarket stroker crank, you must use a 400ci balance damper
     
  21. unkledaddy
    Joined: Jul 21, 2006
    Posts: 2,865

    unkledaddy
    Member

    If you go to this website and pick out a fan, click on dimensions and a
    new page will appear that gives you the exact dimensions with drawings.
    Not all, but most have dimensions available.
    Click here: The Fan Man
     
  22. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 5,615

    Ebbsspeed
    ALLIANCE MEMBER

    The damper is NOT just a mounting surface for the crank pulley. A damper is actually TWO things. The center, or the hub, is normally used to mount the crankshaft pulley. The outside ring is the "damper". It is a "resonant" device that is intended to cancel out the torsional vibration (twisting) that the crankshaft experiences due to the inertial forces of pistons changing directions in milliseconds, combustion impulses, etc. That rubber polymer which bonds the hub to the damper ring is designed to flex near or at the same frequency the engineers calculated the worst crankshaft harmonics to be. So is it a good idea to interchange dampers? Probably not, but it is done all the time, and most engines that it is done on survive without incident.

    By the way, an engine with PERFECT dynamic balance still has torsional vibration when it is running.

    One more point. The dampers on the externally balanced engines provide the two functions mentioned above, but also provide a third function. Think of it as a "wheel weight" (along with the flex plate balance weight on the other end of the crankshaft) to help balance the rotating assembly.
     
    Last edited: Jan 25, 2011
  23. unkledaddy
    Joined: Jul 21, 2006
    Posts: 2,865

    unkledaddy
    Member


    This is unlike an internal balance configuration where the harmonic dampener or flywheel do not contribute to the balance of the crankshaft and are not required to be installed when the crankshaft is balanced.
     
  24. Mr48chev
    Joined: Dec 28, 2007
    Posts: 30,068

    Mr48chev
    ALLIANCE MEMBER

    The front mounting surface of the balancer will be the same on any of the sbc balancer. If you have room for it I'd leave it and just put the short pump and correct pulleys on. That will mean you also have to move the alternator to the drivers side (US) of the engine or buy special brackets for the right side with the short pump.

    Guys usually swap to the smaller balancers for clearance between the balancer and the crossmember on some vehicles. Or as stated by a couple of the guys previously for rotating weight reduction. I've seen central Texas dirt trackers just run the hub but that is pretty iffy for anything on the street.
     
  25. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 5,615

    Ebbsspeed
    ALLIANCE MEMBER

    Other than the flex plate and the damper playing a role in the dynamic balance of the rotating assembly, it is EXACTLY the same.

    Do not confuse "harmonic balancing" with "rotating assembly" balancing. They are two completely different things. I don't know who first started calling the harmonic damper a "harmonic balancer", but they sure have caused a lot of confusion with what the real role of the damper is.
     
  26. unkledaddy
    Joined: Jul 21, 2006
    Posts: 2,865

    unkledaddy
    Member

    Thanks for the info.
     

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