The Hines HC-500 Balancer utilizes a rugged hard-bearing suspension that
gives high sensitivity and permanent calibration. Part set ups are menu
driven, allowing an operator to quickly change between single- and two-plane
balance operations. With the addition of the drill option, on-machine corrections
are fast, accurate and easy. The balancer will calculate amount, angle
and multiple-hole corrections.
Balancing goes hand-in-hand with performance engine building. Balancing
reduces internal loads and vibrations that stress metal and may eventually
lead to component failure. But is it worth the time and effort for mild
performance applications, everyday passenger car engines or low-buck rebuilds?
From a technical point of view, every engine regardless of the application
or its selling price can benefit from balancing. A smoother-running engine
is also a more powerful engine. Less energy is wasted by the crank as it
thrashes about in its bearings, which translates into a little more usable
power at the flywheel. Reducing engine vibration also reduces stress on
motor mounts and external accessories, and in big over-the-road trucks,
the noise and vibration the driver has to endure mile after mile.
Though all engines are balanced from the factory (some to a better degree
than others), the original balance is lost when the pistons, connecting
rods or crankshaft are replaced or interchanged with those from other engines.
The factory balance job is based on the reciprocating weight of the OE
pistons and rods. If any replacements or substitutions are made, there’s
no guarantee the new or reconditioned parts will match the weights of the
original parts closely enough to retain the original balance. Most aftermarket
replacement parts are "balanced" to the average weight of the
OEM parts, which may or may not be close enough to maintain a reasonable
degree of balance inside the engine. Aftermarket crank kits are even worse
and can vary considerably because of variations within engine families.
If the cylinders are worn and a block needs to be bored to oversize, the
larger replacement pistons may be heavier than the original ones. Some
piston manufacturers take such differences into account when engineering
replacement pistons and try to match "average" OE weights. But
others do not. Most high performance pistons are designed to be lighter
than the OE pistons to reduce reciprocating weight for faster acceleration
and higher rpm. Consequently, when pistons and rods are replaced there’s
no way of knowing if balance is still within acceptable limits unless you
If you’re building a stock engine for a passenger car or light truck
that will spend most of its life loafing along at low rpm, your customer
might question the value of balancing such an engine. But if you the customer
value durability and smooth operation, the decision to balance should not
be to difficult.
On the other hand, if you’re building a performance engine, a stroker
engine or an engine that’s expected to turn a lot of rpm's or run
a lot of miles, balancing is an absolute must. No engine is going to survive
long at high rpm's if it’s out of balance. And no engine is going
to last in a high mileage application if the crank is bending and flexing
because of static or dynamic imbalances.
Forces In Action
To better understand the mechanics of balancing, let’s look at the
theory behind it. As everybody knows, a rotating object generates "centripetal
force." Centripetal force is an actual force or load generated perpendicular
to the direction of rotation. Tie a rope to a brick and twirl it around
and you’ll feel the pull of centripetal force generated by the "unbalanced" weight
of the brick. The faster you spin it, the harder it pulls. In fact, the
magnitude of the force increases exponentially with speed. Double the speed
and you quadruple the force.
The centripetal force created by a crankshaft imbalance will depend upon
the amount of imbalance and distance from the axis of rotation (which
is expressed in units of grams, ounces or ounce-inches). A crankshaft
with only two ounce-inches of imbalance at 2,000 rpm will be subjected
to a force of 14.2 lbs. At 4,000 rpm, the force grows to 56.8 lbs.! Double
the speed again to 8,000 rpm and the force becomes 227.2 lbs.
This may not sound like much when you consider the torque loads placed
upon the crankshaft by the forces of combustion. But centripetal imbalance
is not torque twisting the crank. It is a sideways deflection force that
tries to bend the crank with every revolution. Depending on the magnitude
of the force, the back and forth flexing can eventually pound out the main
bearings or induce stress cracks that can cause the crank to snap.
Centripetal force should not be confused with "centrifugal" force,
which is the tendency of an object to continue in a straight trajectory
when released while rotating. Let go of the rope while you’re twirling
the brick and the brick will fly off in a straight line (we don’t
recommend trying this because its difficult to control the trajectory of
Back to centripetal force. As long as the amount of centripetal force
is offset by an equal force in the opposite direction, an object will rotate
with no vibration. Tie a brick on each end of a yardstick and you can twirl
it like a baton because the weight of one brick balances the other. If
we’re talking about a flywheel, the flywheel will spin without wobbling
as long as the weight is evenly distributed about the circumference. A
heavy spot at any one point, however, will create a vibration because there’s
no offsetting weight to balance out the centripetal force.
This brings us to another law of physics. Every object wants to rotate
about its own center of gravity. Toss a chunk of irregular shaped metal
into the air while giving it a spin and it will automatically rotate
about its exact center of gravity. If the chunk of metal happens to be
a flywheel, the center of gravity should be the the flywheel’s
axis. As long as the center of gravity for the flywheel and the center
of rotation on the crankshaft coincide, the flywheel will spin without
But if there’s a heavy spot on the flywheel, or if the flywheel
isn’t mounted dead center on the crank, the center of gravity and
axis of rotation will be misaligned and the resulting imbalance will create
Okay, so how does all this scientific mumbo jumbo translate into the real
world dynamics of a spinning crankshaft? A crankshaft, like a flywheel,
is a heavy rotating object. What’s more, it also has a bunch of
piston and rod assemblies reciprocating back and forth along its axis
that greatly complicate the problem of keeping everything in balance.
With inline four and six cylinder engines, and flat horizontally opposed
fours and sixes (like Porsche and Subaru), all pistons move back and forth
in the same plane and are typically phased 180° apart so crankshaft
counterweights are not needed to balance the reciprocating components.
Balance can be achieved by carefully weighing all the pistons, rods, wrist
pins, rings and bearings, then equalizing them to the lightest weight.
On V6, V8, V10 and V12 engines, it’s a different story because the
pistons are moving in different planes. This requires crankshaft counterweights
to offset the reciprocating weight of the pistons, rings, wrist pins and
upper half of the connecting rods.
Internal or External
With "internally balanced" engines, the counterweights themselves
handle the job of offsetting the reciprocating mass of the pistons and
rods. "Externally balanced" engines, on the other hand, have
additional counterweights on the flywheel and/or harmonic damper to assist
the crankshaft in maintaining balance. Some engines have to be externally
balanced because there isn’t enough clearance inside the crankcase
to handle counterweights of sufficient size to balance the engine. This
is true of engines with longer strokes and/or large displacements.
If you’re rebuilding an engine that is internally balanced, the
flywheel and damper have no effect on engine balance and can be balanced
separately. But with externally balanced engines, the flywheel and damper
must be mounted on the crank prior to balancing.
You should find out what type of engine balance you have (internal
or external), and be cautious about indexing the position of the flywheel
if you have to remove it later for resurfacing. Owners of externally balanced
engines should also learn about installing different flywheels or
dampers and how it can upset balance.
In recent years, the auto makers have added balance shafts to many four
and six cylinder engines to help cancel out crankshaft harmonics. The
counter-rotating balance shaft helps offset vibrations in the crank created
by the firing sequence of the engine.
On these motors, make sure the balance shaft is correctly "phased" or
timed to the rotation of the crank. If the shaft is out of sync, it will
amplify rather than diminish engine vibrations.
Balance shafts are not a substitute for normal engine balancing, nor do
they reduce the vibration and stress the crankshaft itself experiences
as it turns.
The process of balancing begins by equalizing the reciprocating mass in
each of the engine’s cylinders. This is done by weighing each piston
on a sensitive digital scale to determine the lightest one in a set.
The other pistons are then lightened to match that weight by milling
or grinding metal off a non-stressed area such as the wrist pin boss.
The degree of precision to which the pistons are balanced will vary from
one engine builder to another, and depends to some extent on the application.
But generally speaking pistons are balanced to within plus or minus 0.5
grams of one another.
Next the rods are weighed, but only one end at a time. A special support
is used so that the big ends of all the rods can be weighed and compared,
then the little ends. As with the pistons, weights are equalized by grinding
away metal to within 0.5 grams. It’s important to note that the direction
of grinding is important. Rods should always be ground in a direction perpendicular
to the crankshaft and wrist pin, never parallel. If the grinding scratches
are parallel to the crank, they may concentrate stress causing hairline
cracks to form.
On V6 and V8 engines, the 60 or 90 degree angle between the cylinder banks
requires the use of "bobweights" on the rod journals to simulate
the reciprocating mass of the piston and rod assemblies. Inline four and
six cylinder crankshafts do not require bobweights. To determine the correct
weight for the bobweights, the full weight of a pair of rod bearings and
the big end of the connecting rod, plus half the weight of the little end
of the rod, piston, rings, wrist pin (and locks if full floating) plus
a little oil are added together (100 percent of the rotating weight plus
50 percent of the reciprocating weight). The correct bobweights are then
assembled and mounted on the crankshaft rod journals.
The crankshaft is then placed on the balancer and spun to determine the
points where metal needs to be added or removed. The balancer indexes the
crank and shows the exact position and weight to be added or subtracted.
The electronic brain inside the balancer head does the calculations and
displays the results. The machines we have use graphical displays that
make it easy to see exactly where the corrections are needed.
If the crank is heavy, metal is removed by drilling or grinding the counterweights.
Drilling is usually the preferred means of lightening counterweights, and
a balancer that allows the crank to be drilled while still on the machine
can be a real time saver.
If the crank is too light, which is usually the case on engines with stroker
cranks or those that are being converted from externally balanced to
internally balanced, heavy metal (a tungsten alloy that is 1.5 times
as heavy as lead) is added to the counterweights. This is usually done
by drilling the counterweights, then press fitting and welding the heavy
metal plugs in place. An alternate technique is to tap the hole and thread
a plug into place. Drilling the holes sideways through the counterweights
parallel to the crank rather than perpendicular to the crank is a technique
many prefer because it prevents the metal from being flung out at high
After drilling, the crankshaft is again spun on the balancer to determine
if additional corrections are required. If the crank is for an externally
balanced engine (such as a big block Chevy), the balancing will be done
with the flywheel and damper installed. On internally balanced engines,
the flywheel and damper can be balanced separately, or installed on the
crank and balanced as an assembly once the crank itself has been balanced.
New machinery has been introduced that both simplifies the balancing process
and increases the accuracy of the job. Electronic equipment that allows
accurate measurement of not only the amount of unbalance force, but also
accurately reports the unbalanced vector position is now available to engine
rebuilders. Typically, balancing machines have assumed that the unbalance
force was equally opposed, so they would require the technician to correct
the excessive amounts of unbalance on the excess side to the point of making
them equal. Technicians have had to ‘stair-step’ the corrections
equally until the final tolerance was attained.
Technology such as that in the Hines HC 500 eliminates this requirement.
Software and hardware are combined to allow radical differences to be reported
at each end of
the crankshaft (including any rotational positioning or vector position
of the unbalanced force). Because the position and unbalance amounts are
reported correctly the technician can make changes to the crankshaft with
confidence that he will not over shoot the correction. In most cases the
required cycles of analysis and correction are reduced by 80 to 90 percent.
The unbalance amount and position are imported into a special computer
program called "Heavy Metal Analysis" (HMA). This program allows
the technician to plot the position and amount of material that will be
required to correct the crankshaft. The program lets rebuilders create
multiple scenarios based on rotation and radius position, weight amounts
and sizes of Mallory – all of which can be simulated without having
to cut the first chip.
How long does it take to actually balance an engine? A typical Chevy small
block V8 might take anywhere from 45 minutes to an hour-and-a-half depending
on how much work is needed and the degree of accuracy you’re trying
to achieve. You’re obviously going to spend more time on a motor
that’s going into a NASCAR Winston Cup racer than one that’s
going into Grandma’s grocery getter.
Though a balancing accuracy of plus or minus one gram is typically good
enough for most production street engines, many balancers today can achieve
balancing accuracies in the tenths or even hundredths of a gram!
The most time-consuming part of the job is weighing and matching the pistons
and rods. A four cylinder engine takes half as much time for this step
as a V8. The next most time consuming part is making up the bobweights
for a V6 or V8. This step isn’t needed with a straight six or four.
The actual setup on the machine takes only a few minutes, and the initial
spin and readings take only a couple of minutes more. The time required
to perform the necessary weight corrections will depend on the crank (weight
removal goes much faster than adding weight). And if you’ve done
your work carefully, the final spin will require no further corrections
because the balance will be right on the mark.
Most shops charge $150 to $300 to balance a V8. If heavy metal is required,
add $40 to $75 per slug. Some shops charge less to balance engines, but
these tend to be shops that are trying to compete in the budget rebuild
market, not the performance market and they are using old soft bearing technology. .
At RPM Machine we charge $210.00 for a standard V/8 and
V/6 (2 more bob weights). This price will take care of balancing a rotating
assembly up to 40 grams out of balance. For performance race engines and
stroker assemblies that are farther out than this a price per hour will
For more information or to schedule your engine for balancing please feel
free to give us a call at 1-877-354-3812 and we look forward to helping