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chief advantage of an aluminum high performance flywheel
is weight saving. In weight saving, aluminum is the most
potent medium we have available in flywheel manufacture.
Using aluminum sheds 10-15lb from the rotating assembly
of a conventional steel flywheel, but it is the effect the
weight loss has on the moment of inertia—the measure
of an object's resistance to changes to its rotation—that
contributes the real gains. The lower moment of inertia
in the aluminum flywheel provokes an instant response, delivering
not only faster acceleration and faster deceleration but
also suppressing wheel spin. In addition the component is
not very expensive and the installation process not very
Ram Clutches, a competition clutch and flywheel manufacturer
since the early 1970s, designs their aluminum flywheels
as re-buildable units. Moreover they feature a thick ¼-inch
mild steel friction insert to dissipate heat faster, maintain
a flat friction surface, and reduce the likelihood of distortion.
Thinner, un-ground inserts have a tendency to buckle under
the severe heat of hard clutch duty. Though replacement
inserts can be renewed by the factory, rarely do the flywheels
require them. Typically they are resurfaced on a Blanchard
grinder when wear exceeds 0.015in, and this resurfacing
process could be applied several times over if necessary.
“You may not think there is much difference between
a 3/16in thick steel insert and a 1/4in thick insert, but
the difference is huge,” insists Ram’s technical
director Pat Norcia. “The 1/4in thick material with
33 percent more metal to dissipate the heat ensures clutch
engagement remains smooth. A common problem with thinner
3/16in inserts is that they don’t always remain flat.
As the heat builds, distortion occurs and the lighter plate
lifts between the rivets. This leads to reduced clearance
of the clutch disc. Also if the surface doesn’t remain
flat, a smooth clutch engagement is compromised. Clutch
chatter will occur if one area is high, which makes the
clutch grab unevenly and chatter follows.”
Aluminum flywheel blanks are derived from 6061 material
with a T6 temper, and they arrive at Ram’s facility
in Columbia, SC in a variety of thicknesses and diameters
from 12.5 to 15 inches. They are classified by their diameter
and by the number of teeth on the starter ring gear that
encircles them. The most popular blanks are 13.5 and 14
inches. The smallest of these suit the 2300/2000 Ford (135
teeth) and the largest are used on the big-block Fords (184
teeth). The most popular flywheel for a Chevrolet carries
a 168-tooth ring gear and is produced from a 13.5in blank
as is a Ford with a164-tooth gear. The Chrysler unit usually
features a 143-tooth ring gear and is machined from a 13.750in
Flywheels provide 50 percent of the friction surface to
which the clutch disc mates; therefore, they contribute
half of the holding power of the clutch system. Premium
flywheels possess four essential elements: a proper friction
surface finish, a perfectly flat friction surface, a friction
surface parallel to the crankshaft flange, and a fine balance.
Approximately 1 in 20 flywheels is endowed with perfect
balance; the remaining 19 will display drilled balance holes.
Ram’s Pat Norcia reports they balance their units
to within half-oz/inch. “To
provide a proper friction surface and to ensure the flywheel
is parallel to the crankshaft flange,” says Norcia,
“we use a Blanchard grinder that enables us to grind
the flywheels flat to within 0.001in.” A Blanchard
grinder not only spins its grinding head but also its table
with the flywheel attached. By rotating the flywheel and
the grinding stone in two different directions, a perfect
mating surface is achieved. With a 36-grit grinding stone
this device provides a true surface, hence smoother clutch
engagement and greater clutch longevity.
On the edge of the flywheel a groove is machined to accept
a starter ring gear and on its back face three button-head
securing screws are installed after the ring gear is heat-expanded
then shrunk in place. The securing screws offer a safety
margin on competition cars by keeping the ring gear from
rotating on the flywheel. “If for some reason,”
comments Norcia, “the flywheel is exposed to excessive
heat, perhaps through severe clutch slippage, the ring gear
could become loose as the cooling rates of the steel ring
gear and the aluminum flywheel differ. For this reason Ram
fits retaining screws.” He added that on billet competition
drag racing clutches, were slipping is normal practice,
retaining screws are essential.
The principal failings on aftermarket high-performance aluminum
flywheels are often a steel friction insert of inadequate
thickness (usually 3/16in), the omission of a properly ground
surface on the friction insert, and the lack of balancing.
To survive these hazards here in this series of pictures
is how Ram Clutches makes their high-performance lightweight
blanks are received in a variety of thicknesses and diameters
from 12.5 to 15 inches. Derived from aluminum type 6061
with a T6 temper the sawn discs are classified by their
diameter and by the ring gear that surrounds them: 15in/184
teeth suits big-block Ford.
machining of the flywheel blank establishes the outer diameter
and the inner areas where the crank flange pattern will
be drilled. Carbide-tipped cutting tools have the durability
to machine about 90 flywheels before they’re replaced.
Note: the dispersal of the small chips which take away the
heat, keeping the flywheel cool.
ensure the insert dissipates the heat generated by the clutch
system, RAM uses a ¼-inch thick steel insert on all
their aluminum flywheels to avoid distortion. Here 18 rivet
holes are provided to ensure the 1/4in thick insert remains
orbital riveter has a spinning tool in the head, so it rotates
as it compresses the rivets, ensuring a tight rivet bond
between the 1/4in thick steel insert and the flywheel.
an oxy/acetylene blow torch, ring gears are heated and expanded
allowing them to fit over the flywheels.
the ring gear is hot, it is dropped onto the flywheel ring
gear groove. When it cools it shrinks and tightens to the
flywheel, giving an interference fit of 030in.
the back of the flywheel in three places facilitates securing
screws that prevent the ring gear moving on the flywheel.
These offer a safety margin on street-strip cars, but on
drag racing cars where clutch slippage is a requirement
they are essential.
not universal practice among all aftermarket flywheel makers,
final balancing in the form of shallow drilled holes endows
the flywheel with perfect harmonics.