> From:    <VW4X4@VERIZON.NET>
> Date:    Wed, 2 May 2007 07:19:14 -0400
>
> Well I guess I wasn't very clear..... 4 cly. engines are and can not
> ever be balanced.

FWIW, Bosch agrees with you.  The Bosch "Automotive Handbook" has a
section on engines that discusses balancing.  There is a table showing
various engine designs with "free forces of the 1st/2nd order" and "free
moments of the 1st/2nd order".  If I understand it correctly, "order" is
another way to say "harmonic" - 1st order forces are proportional to the
speed of the engine, 2nd order forces are proportional to twice the
speed of the engine, etc.  Apparently these can go quite a way up, but
the book says that usually only the 1st and 2nd orders are big enough to
matter.  It looks like "free forces" tend to shake the engine, while
"free moments" tend to produce extra "push" in the crankshaft output.

All of the engines listed have zero "free forces of the 1st order".  The
only engine that has a non-zero "free forces of the 2nd order" is the
in-line 4 cylinder with 4 crankthrows.  (I think this is the "second
harmonic" that John Reddick mentioned.)  The "free moments" columns are
more variable; the I-4 has zero in both, while a 4-cylinder boxer with
4 crankthrows has zero "free moments of the 1st order" and a non-zero
"free moment of the 2nd order".

The only engines that have zero in all four columns are the I-6 with 6
crankthrows, the boxer 6 with 6 crankthrows, and the V-12 with 6
crankthrows.  A 90 degree V-6 with 3 crank throws has a note that the
free moments of the 1st order "can be completely balanced by using
counterweights", but that its non-zero free moments of the 2nd order
cannot be balanced out.  A 90 degree V-8 with 4 crank throws in two
planes has the same "can be balanced out" note on its free moments of
the 1st order, zand zero free moments of the 2nd order.

If you're a car geek, you might enjoy the "Automotive Handbook".  It is
_NOT_ a repair or "how to" manual, but rather a series of articles on
most of the engineering considerations that go into building a car.  The
authors are almost all engineers and a lot of them are doctorate engineers.
Most of them work for Bosch, with (in the 4th edition) some from Mercedes-
Benz, BASF, VW, Behr, Mann+Hummel, Eberspaecher, Pierburg, BMW, ZF,
Continental, Blaupunkt, and TUeV.  I think the 6th edition is the most
recent one.

Matt Roberds