[Shotimes] interesting read (I hope) balancing-few more questions

Wed, 25 Aug 2004 23:11:54 -0400

Yes and no.

An engine (or motor if you prefer) is different than a tire in that it has a
reciprocating assembly as well as a rotary assembly.  Any reciprocating
assembly will exhibit what is referred to as a "critical speed"  This is a
point where the assembly produces a harmonic vibration that can be quite
violent.  You can change the speed at which the harmonics occur by changing
the balance speed and the weight of the different pieces of the entire
assembly.  So, in theory it is possible to balance an assembly for higher
RPM's and introduce a low speed harmonic vibration.

Jim

-----Original Message-----
From: shotimes-admin@autox.team.net [mailto:shotimes-admin@autox.team.net]
On Behalf Of Paul L Fisher
Sent: Wednesday, August 25, 2004 2:44 PM
To: 'Ian Fisher'; techsho@topica.com; shotimes@autox.team.net
Subject: RE: [Shotimes] interesting read (I hope) balancing-few more
questions

This is a fairly well educated guess. If it is high speed balanced, it is
low speed balanced. Think about tire balancing. If you balance them for 100
MPH, they are smooth all the way. If you balance them at 40 MPH, there is a
chance they will wobble at 100.

Paul L Fisher

1999 Ford Taurus SHO TR 68K - Kirk'ed 2/29/04.

 - Amsoil Series 2000 0W-30
 - Amsoil TS-124 Oiled Foam air filter

Visit my website: http://www.paul-fisher.com
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Amsoil dealer: http://www.paul-fisher.com/oil

-----Original Message-----
From: shotimes-admin@autox.team.net [mailto:shotimes-admin@autox.team.net]
On Behalf Of Ian Fisher
Sent: Wednesday, August 25, 2004 12:58 PM
To: techsho@topica.com; shotimes@autox.team.net
Cc: sho32@yahoo.com
Subject: [Shotimes] interesting read (I hope) balancing-few more questions

Hi again

Background info is at the top, questions at the
bottom:

:)

First off, a big thanks to everyone who has been
helping by answering my questions. My engine buildup
has been going smoothly so far. The one machine shop
called and my crank/rods/pistons and 3.2 oil pump are
in beautiful shape. They are now cleaned and ready to
be sent to the shop that will balance them.

What I have learned about balancing so far (mixed in
with some stuff I already knew). Basically all the
rods are weighed separately and the lightest rod is
chosen as the target weight. All the other rods will
have a few grams shaved off or drilled off the bottom
to hit that target weight. The shop does take into
account the weight of the rod bearings and the piston
rings as I did need to supply two bearing halves and a
set of rings. The weight of the pistons also fit into
the equation.

Ok-after that is done (static balance I guess it's
called), the crank is then put onto a special machine.
Weights which were referred to as bob weights? are
then placed onto the crank rod journals. I believe
that these have some sort of special sensors in them.
The weight of the bob weight is determined by the
weight of the balanced rods and this figure is keyed
into the balancing computer. The crank is then spun up
and the computer will tell the operator where weight
needs to be removed from the crankshaft. I suppose
this would then be referred to as the dynamic balance.
This basically balances the rods to the crankshaft as
one entire assembly. This is great for any motor
buildup but necessary for me since I am using 5 rods
and pistons from one motor a crank from another motor
plus a spare rod and piston from another motor. 

Ok-that is what I know-This is what I don't know:

I was told that a high speed balance (recommended to
me by John Hrinsin) would create a balanced condition
at high engine speeds but a slight imbalance at idle
and lower engine speeds. Is this true? Is it possible
to balance the bottom end for both high and low
speeds? The guy I am working with is on the ball but
since he doesn't balance the stuff himself he is not
sure. I am glad that he is honest. He said that he
will check with the balance guy and quiz him some more
on this when he picks up my rotating assembly tonight.

..and just offhand, does anyone know typically how
much weight should be removed from a rod to achieve a
high speed balance? I guess this question is
impossible to answer since nobody has my rotating
assembly in front of them. I was told that there are
different equations for a standard dynamic balance vs.
high speed dynamic but there may be some middle ground
for achieving a balance all across the rev band. I
hope that someone can help clarify this for me.

Ahh..and for the last time, us V6'ers are internally
balanced, right?

-and my last question doesn't deal with balance but I
was curious anyway-Were the V6 SHO rods forged as one
piece and broken at the factory? I noticed out the
p/n#'s are stamped on the sides of the rods on both
halves of the bearing holders which made me wonder if
that was done with the rod bolted together as two
pieces or if it was stamped while the rod was one
piece and then broken in two. I know that this is a
common practice on some motors like the GM LS1 and the
V8 SHO motor?

Thanks again!
Ian

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