are the core of the engine. Because of that,
they should, by all accounts be rock solid.
Although they're regularly viewed as an unyielding,
immovable object, in reality, that's not the
case. The crankshaft twists and bends relative
to the loads placed upon it by the respective
pistons and rods on each throw. In testing by
an industry giant, General Motors have shown
that the crank in a 350 cubic inch small block
prepped for racing can deflect considerably
at 8,000 RPM. There's more too. A crankshaft
also has natural frequencies. Coupled with the
frequency of the torque inputs and resonance,
severe crankshaft vibrations can result. What
happens next? Outright crankshaft failure if
a damper of some sort isn't used to still these
vibrations. It wasn't that long ago that one
found aluminum hubs on the nose of a drag race
engine. Bad idea. The end result was often a
multiple piece crank.
A label you'll want to
see on an aftermarket damper is this
SFI Specification tag. According to the NHRA
Rule Book, certified
dampers are mandated in many classes of competition.
Why? Simple. Some OE dampers are prone to self-destruction,
particularly if they're old or worn out.
THE GOOD, THE BAD, & THE UGLY
We're not quite done yet. There's more here
than outright crankshaft carnage. When harmful
crank vibrations aren't kept in check, then
valve timing can be disturbed (often
wet sump oil pump gears can shatter, oil pump
drive shafts can break, timing chains can stretch
and self-destruct and shifting gears in a stick
shift combination can become impossible, or
at the very least, decidedly difficult. Main
bearing wear is common when the vibes aren't
controlled. Quite regularly the thrust surface
of the main bearing shows signs of major degradation.
Evidence of main cap to block fretting, chafing,
or galling is also common. Rod bolts can continually
loosen. Ditto for little things like valve cover
bolts. Rod bearings can blacken. Valve spring
life can become dismal. Flywheel and converter
bolts can loosen. Flywheels can physically break.
The torque converter pilot or hub to gear surface
can fret or chafe. In general, plenty of ugly
things can happen due to bad vibes.