Drag Illustrated Issue 139, December 2018 | Page 72

DI TECH
SIDESTEP THE WEAK LINK
R
CALLIES PERFORMANCE PRODUCTS INTRODUCES
NEW SPLINED CRANKSHAFT
acing proves the weakest
link of a chain will always
break first. It’s part of go-
ing faster. Smart racers stay
ahead of breakage by using products
that strengthen those weak links. This
is the case in Callies’ new splined
crankshafts. Callies is already known
for their bulletproof crankshafts and
by them incorporating a spline on the
snout, or post of the crank, they’ve
taken the next evolutionary step in
making them even stronger.
The problems first surfaced in Top
Fuel, Funny Car, and bigger classes in
tractor pulling with their use of higher
volume superchargers. Typically, these
blowers are the largest in motorsports.
Using them creates a problem where
the torsional load of the crank pulley
exceeds the capabilities of standard
keyed configurations for retaining a
blower drive pulley on the crankshaft.
Simply put, the bigger blowers were
overpowering the keys and keyway
mountings of the blower pulley on
the crank. Pulleys in such applications
are seeing the maximum amount of
torque and those numbers are not
going to get any smaller. So, how do
you make the pulley/crank connection
stronger to support such loads?
We first need to understand how
crankshafts without a spline use a
standard round post with two keys,
set in their keyways, 180 degrees from
each other. These keys are intended to
provide alignment between the pulley
and crank. The problem is they can
only offer minimal resistance to rota-
tional forces because the keys can only
“hold” the pulley with the totaled com-
bined square inches of surface area of
the keys and keyways. And as blowers
put out more and more power, the loads on that
connection are increased. As power increases,
pulleys and belts get bigger and stronger, too. It
all adds up to more force on keys and keyways.
Specifically, all the torsional forces directed
to the keys center themselves on the keys and
sides of the keyways. It’s much like the contact
patch for tires. More contact can mean more
traction for tires, but in the keyways, it means
more forces drilling down into those keyways.
On top of that, keys and keyways are subjected
to torsional forces in alternating directions as
the crankshaft rotates. Half the time, the post is
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being turned downward 180 degrees. Then, as
the crank rotates, it reverses the direction of the
forces and is pushed upward 180 degrees. Inside
the keyway, the forces are pushing the key back
and forth in the keyway. If there is any slop in the
keyway, these forces will increase any tolerances,
furthering wear and slip on the blower drive pul-
ley. In less than 10 runs, keys and keyways can
begin the wear-equals-damage cycle.
The solution was to take that load off the keys
and keyways and distribute it over the entire post
area. Using a spline does just that, dispersing
the load over 100 percent around the post. By
comparison, the key system has only the square
inches of the two keys and keyways to support the
pulley while the spline, with typically 33 “teeth,”
covers the entire 360 degrees of the post.
The benefits of using a splined drive are numer-
ous. One is the core strength of the post is now
increased. Because of the use of surface area and
its increased strength spread out over the entire di-
ameter of the post, splines don’t need to penetrate
as deep into the material of the crank post as much
as typical keyways. Splined crankshafts provide an
increase in cross section material between the bot-
tom of the spline and the post bolt hole compared
Issue 139