What is the theory behind an engine that is external balanced. What is the difference in how the parts work together i.e. harmonic balancer, crank, flywheel versus internal balanced? It seems each part would still be individually balanced.
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Re: External Balance
it is because it would hard(expensive)to do it internally because there is not enought room for large(heavy) enought counterweights on the crank. these can be internally balance but you must use heavy metal(tungsten/expesive)plugs to get the weight of the counterweights heavy enought to balance out the pistons and rods. all race engines are internally balance but it is cheaper fot the car companies to do it externally -
Re: External Balance
Larry-----
Basically, an internally balanced engine is one in which all of the reciprocating parts are "neutral balanced". So, when everything is assembled, the resulting assembly is balanced. Most Chevrolet small blocks are so-balanced except 400 cid.
In an externally balanced engine, the harmonic balancer and flywheel are not neutral-balanced, but, instead, have integral counterweights (some aftermarket pieces have removeable counterweights). The reason that external balance is used is that it avoids the need (and expense) of neutral-balancing the internal components (mainly the crankshaft) of certain engines, usually those of relatively long stroke. In order to neutral balance certain crankshafts, the use of expensive "Mallory Metal" and labor-intensive balancing operations would otherwise be required. For PRODUCTION, this is, obviously, undesirable. Chevrolet small block 400 cid and big block 454 and 502 are examples of externally balanced engines. Externally balanced engines like these can be converted to internal balance by neutral-balancing the internal reciprocating assembly, but it requires the above-referenced steps. Actually, internal balance is preferable as it creates less stress on the internal reciprocating assembly parts, especially the crankshaft. But, it's expensive to have done.
By the way, the new Chevrolet 8100 big block engine used in trucks and marine applications beginning with the 2001 model year is a 496 cid engine which is INTERNALLY balanced even though it uses a 4.37" stroke crankshaft. I don't know (yet) how GM achieves internal balance in these engines, though.In Appreciation of John HinckleyComment
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Re: External Balance
Balancing a cruciform crank V-8 is a very complex subject. In fact the math wasn't worked out until sometime in the 1930s.
If the rotating balance mass is equally distributed on each of the four throws, the engine would have a first order rocking couple due to reciprocating mass. By moving some of rotating balance mass from the center throws to the ends of the crankshaft the couple can be balanced. This is evident by viewing a typical V-8 crankshaft. Most of the balance mass is at the ends.
On some long stroke engines there is just isn't enough room for all this concentrated balance mass inside the engine; Thus the need to locate some of it on the damper and flywheel.
DukeComment
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Re: External Balance
Balancing a cruciform crank V-8 is a very complex subject. In fact the math wasn't worked out until sometime in the 1930s.
If the rotating balance mass is equally distributed on each of the four throws, the engine would have a first order rocking couple due to reciprocating mass. By moving some of rotating balance mass from the center throws to the ends of the crankshaft the couple can be balanced. This is evident by viewing a typical V-8 crankshaft. Most of the balance mass is at the ends.
On some long stroke engines there is just isn't enough room for all this concentrated balance mass inside the engine; Thus the need to locate some of it on the damper and flywheel.
DukeComment
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