OK the reason for the V7 is---cheap---what a surprise. If you have all the
V8 parts already it's a ton cheaper to make a spacer/weight than buy the
parts for a V6 or destroker V8. The weight on Jacks crank is at 55% of a
full pin bob weight. Why is this? I don't know. Jack would be the source for
that information or the guy who did his balancing. Rich Fox
----- Original Message -----
From: "Dave Dahlgren" <ddahlgren@snet.net>
To: <ardunbill@webtv.net>
Cc: <land-speed@autox.team.net>; <bigsid@webtv.net>; "marco"
<bk185@lafn.org>; <bjgayle@aol.com>; <byayes5@hotmail.com>;
<clemtebow@jps.net>; <freiburd@emapUSA.com>; <jdcnowell@aol.com>;
<ddferguson@msn.com>; <jamisone@iowaone.net>; <gillette@cccomm.net>;
<larkspur4K@hotmail.com>; <ronnieroadster@aol.com>
Sent: Wednesday, January 30, 2002 06:52 AM
Subject: Re: (Tech) sbc overbalance opinion
> Ok I give up... Why would you build a V-7??
> An engine is never in 'balance' by the way..
> it is only an approximation that shakes the least at the rpm of interest..
> Did the inventor of the V-7 give any thought to the stresses when you have
the
> missing cylinder not fire and the have a time lapse before the next
firing??
> I think you will get something like..
> put..put..put..put..put..put..........bang...
> The instantaneous loading on the crank and drive train may not like this
'gap'
> Oh on the 'overbalance' it is not an over balance or under balance it is
merely a
> shift in the frequency of interest. A trade off between where you think it
is
> important to shake the least. I would think that at max power output I
would want
> my engine to shake the least there are no awards for 'best idle' last i
checked.
> But if you want to be kind to the bearings you would want the least extra
stress
> on them when they are already heavily loaded. The one gram tolerance is
doable
> in everyday production work now also.
> Dave Dahlgren
>
>
> ardunbill@webtv.net wrote:
>
> > Hi Folks, been reading the messages about V8 and V7 crankshaft balancing
> > with interest. Some of the ideas seem confusing to me. I thought I
> > would quote an authority so the novices reading the discussion might
> > understand what is being talked about.
> >
> > P.E. Irving, "Automobile Engine Tuning", Temple Press, London 1963,
> > Chapter 13, "Balancing", p. 141: "V8 crankshafts require dummy weights
> > on each pin; each weight must be equal to the combined weights of the
> > TWO big-ends, plus the top-end weight of ONE connecting-rod and its
> > piston, rings, etc., ..."
> >
> > In this procedure, bobweights as above are attached symmetrically on
> > each crankpin and the crankshaft then rotated at 1000 rpm in a balancing
> > machine. The crankshaft is then corrected by drilling holes or adding
> > "heavy metal" in the counterweights until it is in balance.
> >
> > It is assumed that all four sets of pistons and con-rods have an equal
> > weight to 1 gram and good luck achieving this in practice!
> >
> > The weights of the big and small ends of the con-rods have to be
> > measured horizontally on a frictionless device to get accuracy.
> > Speedway Motors sells such an item for this purpose, how good it is I
> > know not.
> >
> > I imagine that for a V7 a steel sleeve clamped on the crankpin, taking
> > the place of one big-end, to seal the oil hole in the crank and take the
> > side thrust from the working con-rod, and the said sleeve weighed 50% of
> > the original balancing bobweight, then the crank balance would remain
> > correct for all practical purposes.
> >
> > I suppose that the previous messages about 50-51-52% balancing have a
> > relationship to the above information, and perhaps people would verify
> > that for me.
> >
> > The man who does my balancing seems to be willing to do it in accordance
> > with Irving's model. It's his machine, and I can't run it.
> >
> > Cheers from Ardun Bill in the Great Dismal Swamp, Chesapeake, VA, where
> > it's been in the high 60s the last four days so I could get my bike out.
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