Loading ...
Sorry, an error occurred while loading the content.

Engine balance question

Expand Messages
  • Bob Patton
    Are there performance and efficiency benefits to engine balance? Aside from subjective perceptions like noise, vibration, and hashness; do you get more
    Message 1 of 4 , Aug 27, 2008
    • 0 Attachment
      Are there performance and efficiency benefits to engine balance? Aside
      from subjective perceptions like noise, vibration, and hashness; do you
      get more horsepower? Internal vs. external balancing? Even if the engine
      is as calm as a clam on the outside, is there a riot going on inside
      between the crank and case?

      Bob Patton
    • Ken Augustine
      Bob P, Yes, that is all ongoing and depending on dependencies, many things can happen, most of which are either bad or at least undesirable. Unfortunately,
      Message 2 of 4 , Aug 27, 2008
      • 0 Attachment
        Bob P,

            Yes, that is all ongoing and depending on dependencies, many things can happen, most of which are either bad or at least undesirable.   Unfortunately, reciprocating forces simply cannot be balanced completely or even moderately on a component by component basis and that is where loads must be resolved which costs in friction and flex.  

            As an example, take two twenty pound dumbells, hold them at arms length as far apart from each other as you can.   Now bring them together and spread them back far apart as rapidly and for as long as you can without having a heart attack or getting your tongue caught between them.   In a short time you will be huffing and puffing even though the system is in perfect primary, secondary and rocking couple balance, something that even a BMW boxer isn't.   Certainly, the stroke and reciprocating masses are far higher than in a BMW motorcycle engine but the frequency will be far lower.  

             If the reciprocating masses or stroke can be reduced, the resolved forces will be lower which is what creates the friction as with no force to be resolved through the bearings, the friction goes to zero and all that remains is a tiny bit of ring friction as the viscous friction in bearings could be mostly eliminated with the removal of the bearings themselves.

             As it is, a 50% balance factor for each cylinder gives the least overall imbalance force in each piston/cylinder assembly but to keep the masses and thus overall forces as low with the distances between them as small as possible is the best combination.  

        Ken A

        =============================================

        Subject: Engine balance question

        Are there performance and efficiency benefits to engine balance? Aside
        from subjective perceptions like noise, vibration, and hashness; do you
        get more horsepower? Internal vs. external balancing? Even if the engine
        is as calm as a clam on the outside, is there a riot going on inside
        between the crank and case?

        Bob Patton

      • Dan Timberlake
        snipped and bottom posted ... From: Bob Patton ... engine ... ===================================================== The balancing of
        Message 3 of 4 , Aug 29, 2008
        • 0 Attachment
          snipped and bottom posted

          -------------- Original message ----------------------
          From: Bob Patton <bpatton@...>
          > Are there performance and efficiency benefits to engine balance? Aside
          > from subjective perceptions like noise, vibration, and hashness; do you
          > get more horsepower? Internal vs. external balancing? Even if the
          engine
          > is as calm as a clam on the outside, is there a riot going on inside
          > between the crank and case?
          >
          > Bob Patton
          =====================================================

          The balancing of the pure rotating masses is easy. The leftovers are
          all the pistons' and rods' fault. They tug unevenly on the crank's
          rod journal. "Balancing" does not reduce those forces.

          The balance machine folks used to (60s and 70s) publish all kinds of
          claims for precision engine balancing, including hp and gas mileage
          improvements. I suppose the main bearing loading is reduced by
          balancing, so some small friction reduction might result. I did not
          and do not hold much hope for either one, except in one particular
          case. We balanced a Kawasaki Bighorn engine assembly (crank, rod,
          piston brgs, rings etc) for a local hill climb racer. It was a pretty
          radical engine, using a vintage techniqe of putting a port in the
          exhaust side of the piston skirt timed to let the exhaust pressurize
          the crankcase at some point in the transfer event. Anyhow, like most
          2 strokes it was severely undercounterweighted, so needed a few slugs
          of mallory metal to get it to ~60% balance factor. He raved about how
          it ran after balancing, and won the championship. for a few years in a
          row.

          My suspicion was the "unbalanced" vibration was shaking the rubber
          mounted carburetor enough to shake the gasoline into froth and messing
          up the jetting.

          He had a few more cranks balanced to build engines for himself and
          others. He abandoned the last one at the shop because his customer
          backed out of the prject. I have it in a box someplace. I figure the
          piston is not worth anything to anyone with the crazy boost port
          machine in.

          Dan Timberlake
          Westford, Massachusetts, USA
        • Dave Williams
          ... Balancing won t make any horsepower. All it does is make the engine shape less. ... On a V8 with a 90 degree crank, external balancing will let you get an
          Message 4 of 4 , Sep 2 8:36 AM
          • 0 Attachment
            Bob Patton wrote:
            > Are there performance and efficiency benefits to engine balance? Aside
            > from subjective perceptions like noise, vibration, and hashness; do you
            > get more horsepower?

            Balancing won't make any horsepower. All it does is make the engine
            shape less.


            > Internal vs. external balancing?

            On a V8 with a 90 degree crank, external balancing will let you get an
            apparent balance with less metal than an internal balance. However,
            there are unbalanced couples inside the crankcase, resisted by the
            crankshaft and engine block.

            On an internal balance small block Chevy the #2 and #4 mains get more
            wear than the other three due to this. It's my opinion that "main cap
            walk" at high RPM is a result of load across those couples flexing the
            crank.


            > Even if the engine
            > is as calm as a clam on the outside, is there a riot going on inside
            > between the crank and case?

            Oh, yes!
          Your message has been successfully submitted and would be delivered to recipients shortly.