Re: [AMC-List] An old song is a good song?

[adh@xxxxxxxxxxxxxxxxx (Sandwich Maker)]

" From: "John Elle" <johnelle@xxxxxxxxx>
"  
"  
"  
" Snip
" it is my understanding
" that internal or external balance is a decision made by the designer.
" Even the legendary Chevy small block which is internal balanced as I
" understand, the 400 cu in version of it is externally balanced leaving
" one to do some extra work when installing a 400 crank in a 350 to make
" the popular stroker 383 due to the external balance configuration of the
" 400 crank, as I understand it.
"  
" yeah, but comparing a v to an inline is an apples-and-oranges thing.
" Snip
"  
" Yuh, agreed, but it seems to me that I compared a commonly available
" engine with multiple parts interchangeability that can be found as
" both internal or externally balanced depending on the displacement of
" the thing. 

you did, but i don't see how that's relevant.  chevy shorted the
counterweights on the 400 to make it easier to fit the long stroke
into the crankcase.  the extra counterweight mass must be added to the
flywheel and/or damper.

v8 cranks are commonly not fully counterweighted - eg. weights either
side of every throw - but afaik even internally balanced v8s cannot be
made without some counterweights, and they must be rebalanced whenever
you change rod or piston weight.  the rr silver ghost inline six had
no counterweights.  jeep 'stroker' engines - 4.0 blocks with 258
cranks - can use either 258 rods and 4.0 pistons or 4.0 rods and
custom pistons without rebalancing - and no, the custom pistons aren't
made extra heavy to make up for the lighter 4.0 rods.  [258 rods are
heavy because the forging is also used for v8 rods]

i've heard of several externally balanced v8s but no inline sixes.

i've asked machine shops about balancing a six and they all have told
me they don't need it.  that's not to say they're completely right; in
thinking about it i can see how the whole assembly can be balanced but
have internal unbalances that cancel out.  i'm sure this is why bmw
cranks have 12 equal counterweights.

" The point being, as far as I know there is nothing particularly magic
" about the number of cylinders and whether it is internal or external
" balanced.  A design feature which is most probably a decision made by
" whomsoever designed the thing. 

but there -is- something 'magic' - the fundamental geometry of
cylinder arrangement, and the resulting forces in the various
directions they generate!
________________________________________________________________________
Andrew Hay                                  the genius nature
internet rambler                            is to see what all have seen
adh@xxxxxxxxxxxxxxxxx                       and think what none thought
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