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

[adh@xxxxxxxxxxxxxxxxx (Sandwich Maker)]

" From: "John Elle" <johnelle@xxxxxxxxx>
" 
"  
"  
"  
" Snip
" the more i think about it, the more i'm convinced that all inline
" sixes are internally balanced by their very nature.  i haven't yet
" heard of one that isn't.
" Snip
"  
" Not that this is one of the things that I keep track of as a hobbiest,
" so I could not comment standpoint of knowledge, 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.

" How some ever it was the increasingly popular use of  building and
" installing I-6 engines in some of early 1900 automobiles that lead to the
" invention and refinement of the design of the Harmonic Balancer due to
" the annoying habit of those engines to break crank shafts with out
" provocation. A problem that still prevails today. I am not sure how much
" balance plays a roll in that action, but my gut feeling is that the
" inherent balance design of an I-6 engine is pretty much an urban legend
" leaving the final decision to the method back in to the hands of the
" designer. In any case if I were to work on an I-6 engine other than my
" trusty 232 or 258 , the method of the engine being balanced would be
" about number 1 on my need to know and had better find out quick list of
" things to do. 

now we're talking torsional vibration, which i never thought of as
balanceable.


" From: "Mahoney, John" <jmahoney@xxxxxxxxxxxxxxxxx>
" 
" 
" >>
" the more i think about it, the more i'm convinced that all inline
" sixes are internally balanced by their very nature.
" <<
" 
" Sometimes: depends on when.
" 
" http://zhome.com/ZCMnL/tech/harmonics.htm

an excellent piece and illustrating just what i meant.  i was thinking
of the kind of balancing job hotrodders get on their v8s, trimming or
ballasting the crank counterweights to match piston/rod masses...
that's the stuff an inline doesn't need.  mirroring the crankshaft
about the midplane makes the cylinders balance each other.  okay, it
was a shockingly low rpm motor [-increase- revs to -50- rpm before
engaging clutch] by modern standards, but the '07 rolls royce silver
ghost six had no counterweights at all.

he's wrong about one thing though - radials have only one crank throw
per bank, with one 'master' rod that all the others hang off of, and
-big- counterweights on the throw.  yes, the pistons are all at
different points in their strokes - but they're at different angles
too.  when the crank throw moves up, they all must perforce -move-up-.

now if you had a six-row radial, you could phase the crank like an
inline six...

btw, 4-stroke radials have odd numbers of cylinders per bank - as you
go around the rim every second cylinder fires, and after two circuits
you're back to #1.  kind of like an internal combustion moebius
strip...
--
now i think of it, he's wrong on another point too.  the harmonic
balancer does -not- 'absorb' torsional vibrations; by resonating
properly in tune with them it can turn one large force peak into two
smaller ones on either side on the rpm scale.  'scale' is appropriate;
iirc the new peaks must be an octave apart, eg. 2:1 rpm ratio.
________________________________________________________________________
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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