Hey guys.

Here is an excerpt from an email recently forwarded to me from my old man. The discussion came from the "Standard 1320 Group", a bunch of old and young drag racers- A lot of very famous and experienced ones in it..

The original discussion started on bearing clearances, but I thought this bit was very interesting...

Enjoy.

Let me weigh in on this discussion by mentioning a few items
concerning crankshafts that may provide some insight to your question.
If not some insight, then at least some food for thought.

I am making the assumption that the term ‘whipping’ that has been
tossed around here is in reference to the flexing that occurs in the
crank and shows up as such tale-tell signs as wear on the bearings,
flywheel contacting the motorplate, and blower belt departing the
pulley. The truth is that this distortion comes from more than one
source, not just excessive bearing clearance. Harmonics and/or firing
pulses, which have yet to be mentioned, are large contributors.

A number of years ago I was privileged to observe some tests conducted
by Vibratech, one of the leading manufacturers of harmonic dampers, as
they were working toward introducing their ‘Fluidamper’ to the
performance world. The tests I saw were on a stock 350 Chevrolet
crank. The test engine was highly instrumented and used an optron
(strobe light) to freeze the movement of the crank (to the eye) at
various RPMs. The first thing we saw was that the crank went into
harmonics at three different RPMs throughout the range at which it was
tested. The second thing that got my attention was the amount that the
crank both bent AND twisted when it was in harmonics. As I recall the
crank bent downward between #1 and #3 main, and upward between #3 and
#5 main. That made you want to run right home and look for wear on the
leading and trailing edges of the main bearings. The other thing that
stood out was the torsional twist. Some throws would be out 3 degrees
in one direction, and others out 3 degrees the other direction, for a
combined twist of 6 degrees front to rear. Now here is the kicker, all
of this was occurring at highway driving RPMs, not high load, high RPM
usage. We drive down the highway day-after-day, often at harmonic
RPMs, and never think a thing about it. Ignorance is bliss, right? But
I guarantee you that if you would have removed that crank from your
old Junior Fuel car, in its harmonics induced bent and twisted
configuration, you would have thrown it immediately in the dumpster.
It was a good case of what we didn’t know didn’t hurt us… too much.

The effects of firing pulses, regardless of harmonic, is another case
of the unseen doing strange stuff. We have come to learn that the
crank does not revolve in the engine in a fluid motion. It starts,
speeds up, slows down, stops, starts again, stops again, backs up, and
repeats, all within a single revolution during every cycle. Hard to
imagine, but true. Think of what this is doing to crank twist and cam
timing. Think of detonation and the frequency of blower belts
shredding or flying off the pulleys. Ever gotten out of a four
cylinder car and into a twelve cylinder car? You can feel the
difference in smoothness in the seat of your pants.

Anyway, I guess where I am going with all of this is that crank
‘whipping’ can come from a variety of sources, and one of the first
places it is noticed is in bearing wear. Racers have a habit of going
for the quick fix in such instances, and in this case more clearance,
more oil pressure, and heavier viscosity oil probably got them out of
trouble, so that became the cure-all. If you move that pesky crap
further away where something can’t wear on it or run into it, then
you’ve fixed the problem, right?

As for your question about center counterweighted cranks (and I have a
hunch you already know the answer), it is my belief that they simply
fell out of favor as a result of the search for lighter and lighter
cranks.

All-in-all I’ve enjoyed everyone’s input on this thread. I’m sure
there are many here who have picked up some morsels of information out
of it.