By Don Crafts, MotorCycle Online Chicago Desk
| This article was originally written by Don
Crafts of Motorcycle Online. Full credit goes to Don for this article.
The Motorcycle
Online article contains pictures covering the installation of the torque arm. If you wish
to view the installation procedures, please go to Motorcycle Online's site at any of the
various links established here. The
V-Twin Café 1994 FXDL bike utilizes a Carlini torque arm. I can attest to the
improvements in handling and the effectiveness of keeping the engine and transmission
connections rigid. The need to improve the rigidity and strength of the
engine/transmission on the 1994 FXDL is an absolute requirement when its engine is capable
of putting close to 100 HP and 100 ft.lbs. of torque to the rear wheel.
We apologize for changes made to the original
article. Additional comments from Bike Tech have been added based upon our additional
experience with the Carlini Torque Arm.
News Flash March 1998:
Harley-Davidson now has a torque arm marketed under the name Screamin' Eagle Race
Brace™. Contact your local dealer for availability. |
We know what you are thinking. What on earth is a torque arm?
A good question with an easy answer. A torque arm is an aluminum brace that installs
between the engine and transmission of Harley-Davidson Evolution Big Twins.
Okay, so why would you want one? Well, that one doesn't have such a
easy answer. Let us start with some background information first.
background
Today's Harley riders have more horsepower at their disposal than
ever before. Hopped-up Evo mills routinely register near triple digit horsepower. This is
a good thing. However, the Motor Company does not design its motorcycles to handle twice
their stock power output. This design "weakness" usually shows up first in the
connection between transmission and engine. The transmission of a big twin Harley is
connected to the engine at only two points:
 | the central mounting bosses between them, and |
| the inner primary case on their left. |
In some cases this configuration can lead to an unbalanced loading
of forces. Engine transfer of power to the left side of the transmission causes this
imbalance. As such, the primary chain is in effect trying to pull the left side of the
transmission towards the engine. Normally, the transmission mounting bolts are sufficient
to contain this torque load. However, this configuration was not designed to handle
increased torque generated by a real asphalt ripper. (Bike Tech Note:
What this means is that high power motors can break chain cases!)
how does it work?
What a torque arm does is "unitize" the engine and
transmission. The torque arm connects an Evo's transmission to the right side of its
engine. If you've been following along you will no doubt remember that the inner primary
case connects the transmission to the left side of an Evo engine. Now the transmission is
not only connected by mounting bosses in the center and the inner primary case on the
left, but also by the torque arm on the right. This setup makes all the components happy.
And there are no unbalanced loads lurking around to cause failures.
This arm was designed by Tony Carlini of Carlini Design. Carlini
originally developed the torque arm for his high-powered "Black Bart" custom
Dyna Glide. He had grown tired of replacing primary cases on it. Imagine that.
It is no surprise that this problem first started showing up on
FXDs. Dyna Glide models have an additional reason for needing a torque arm. Look where
Dyna's have their swing arms mounted. They are unique in the world of big twins. A Dyna
Glide swing arm is attached directly to the transmission, rather than its frame. This adds
an additional component of stress to the equation. When cornering, side loading on the
rear wheel is transmitted directly to the swing arm, which on a Dyna then transfers this
load directly to the transmission. Again, in stock form this does not cause any trouble.
But how many people are happy with stock Harley's? (Bike Tech Note: If
you have a Dyna chassis bike with a high power motor, a torque arm is an absolute
requirement. The cost of the torque are is much less than your primary chain case! You
will break the case if you ride hard.)
installation
Installation was almost a snap. All you need to do is remove six
bolts, slap on the arm and install six new bolts. Simple. What makes it a little bit
tricky is that you first have to remove the exhaust system and the transmission cover.
Which exhaust system you have will dictate how difficult the first step is. For this
review we installed the torque arm on a Dyna equipped with Bub's Bad Dog pipes. Removal of
these couldn't be easier.
Opening up the transmission door was more of a trick. The goal is to
tip the bike far enough to the left to keep transmission fluid from leaking out. This was
accomplished by rolling the front wheel up on a five inch riser, then tipping the bike
over on its side stand.
With the pipes off and the transmission door open, installation of
the torque arm was just a matter of removing and replacing six bolts. Three bolts are
removed from the transmission and three bolts from beneath the nose cone. The arm slides
right into place and is installed with six replacement bolts. Re-install the transmission
cover and exhaust pipes and you're good to go. (Bike Tech Note:
Installation on an FXD or FXDL is more complicated. You will need to remove the foot peg
support and brake pedal. Using a 2-into-1 exhaust system will also complicate the
installation.)
performance
The change in ride performance is immediately noticeable -- albeit a
little hard to quantify. You find yourself describing how the bike felt without the torque
arm in terms you would have never used before installing the arm. For example, power
transmission is no longer "spongy." The bike no longer "porpoises"
during quick bursts of acceleration.
Handling is definitely improved. Corners are now something you throw
the bike into. You feel more in control. As mentioned, the change is hard to quantify.
Suffice it to say, while the ride was never bad before, it is definitely better now.(Bike
Tech Note: Expect the ride to feel more firm, with a slight increase in vibration
felt in the foot pegs)
As required by current aftermarket standards, the Carlini torque arm
is fabricated from billet aluminum and comes slathered in flawless chrome. What does all
this mean do for you? Do you need a torque arm? At $289.00 you probably ought to make sure
first. To decide, you need to ask yourself a couple of questions. Such as, "how much
power am I planning on getting out of this Evo?" and "how aggressively will I be
riding it?"
If you're happy with the stock performance of your sled, pass this
by. Its benefits will not be noticed as much as the hole in your wallet. However, if you
bought that scooter to build and ride, the Carlini torque arm should definitely be on your
list. (Bike Tech Note: If your scoot is a Dyna, this piece should be
the second item you put on the bike. What's the first? Why a new set of pipes. Do not add
a cam or do significant engine work without a torque arm.)
Motorcycle Online Rating: ****
The arms are available for all Harley-Davidson Evolution big twins:
FXRs, Dynas, Softails and Electra Glides.
where to get info
Carlini Design
Highway Art Corporation
17516 Von Karmen Avenue
Irvine, CA 92714
(800) 398-0222
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