ENGINE BALANCING FAQ
Why Have Us Balance Your Engine?
Simply put, the main reason is to eliminate damaging and parasitic forces that causes unwelcome
mechanical activity and robs the engine of its ability to freely transmit all of its power directly to the
wheels.
Most people overlook the fact that all engines from the first stage of manufacturing go through some
process of balancing. When the crankshaft and all related components are manufactured they have to be
shaped and weighed to meet a target weight specification.
The crankshaft is then designed with counter weights that offset the thrusting and rotating forces generated
via the combustion activity that causes the engine to rotate. Ok this is generally known and understood.
But what we need to understand is that the engines that were used just a few decades ago were running
at a relatively low RPM band as compared to the engines that we are currently receiving from the
OEM’s. Notice that I am talking about the “Grocery Getter” not Hi-Performance.
Let me give you some information that hopefully will get your attention.
When the OEM’s such as GM, Ford and Chrysler produced a typical vehicle they would generally
accept a balancing specification of 2.0 Ounce-Inch tolerance, so what does that mean.
The 2.0 ounce-inch tolerance means that on a typical crankshaft that has a total diameter of 6.0 inches
it will have 18.95 grams of unbalance weight residually embedded in the outside edge of the counter
weights.
When the engine is running @ 1000 RPM (just above Idle), the embedded weight will cause the rotating
crank assembly to generate a centrifugal unbalance force of 3.56 pounds. As we increase the RPM
to 2000 the unbalance force increases to 14.25 pounds and at 4000 RPM it is now 56.5 pounds and 8000
RPM will generate 228 pounds of force.
Now you must understand even though the unbalance force has increased from 3.56 pounds to 228, the
physical embedded weight of 18.95 is still exactly the same. Only by increasing the RPM can we
increase the generated unbalanced force.
So you say we rarely operate the engine at 4000 RPM thus the 56+ pounds of force is not a big deal.
Well let me explain that if you had a 56 pound hammer and you dropped it on say the hood of your car
you would notice an unwelcome dent. So lets imagine that hood of you car is an engine bearing. This
bearing is receiving a pounding of this 56 pound hammer at a rate of 66+ times per second (4000 RPM).
Even though the bearing can probably handle the pounding force, the energy from this is transferred
into the main bearing housing and it will cause distortion causing a host of new problems, especially
with the newer light weight blocks. So if the bearing in your engine could talk then, …..well I think you
are getting the picture.
So does balancing make horsepower?
No not in direct form, it eliminates parasitic forces that would otherwise increase with higher RPM.
Simply put if the combustion activity of the engine is the source of power then unbalance forces are the
dampening or restricting forces that will waste the engines potential output. Elimination of vibrations
and possible deformation as a result of the pounding activity is a welcomed benefit.
Professional engine builders understand that the unbalance forces change how engine parts interact
with each other.
For instance when Timing Chains were changed to Timing Belts one of the key benefits was that the
belt help dampen the vibration pulses generated from the crankshaft and would eliminate or minimize
their corruptive forces. Thus the camshaft would rotate more freely and would help stabilize the following
activity of the lifter or cam follower.
It should be noted that as we have changed the engine designs and increased RPM and profiles of the
camshaft, the vibration problems have generated a host of activities that are restricting the intended
horsepower and durability increases.
Everyone in racing can agree that most of the major machining techniques and bolt-on parts have
already been developed that will give quick and substantial horsepower increases. The pro engine builders
are now searching for those last little tweaks of change, 1 horsepower at a time.
Balancing has a roll to play in this process, the ability of the engine component to maintain profile
stability goes to its ability to perform as designed. Crankshafts are only one part of the equation.
Let me give you an example: The roller lifter is designed to follow the profile of the camshaft lobe with
absolute accuracy. Consider a vehicle with perfectly balanced and round tires rolling along a smooth
road surface. If you run off the side of the road the tire bounces due to the uneven terrain and as a result
you feel the vibration in the steering wheel, the tire is still balanced but the surface that it is running on
has changed forcing the tire to move in an unusual way loading and unloading the suspension spring
that is carrying the load of the vehicle. Once back on the smooth highway the vehicle smoothes out and
the ride is back to its normal profile.
As stated before the crankshaft is designed to rotate smoothly and it has counter weights positioned to
counteract the unbalance and thrusting forces caused during the running cycle.
You may have noticed that most true V-8 Hi-Performance Crankshafts are fully counter weighted (8
counter weights) this means the each rod journal has its own set of counter-weights. Most “Grocery-
Getters” have 6 counter-weights. The 6 counter-weighted units are a carry-over from the older “stock”
designs; remember they were not designed for high load and high RPM applications and did not generate
large amounts of horsepower.
But all of us know that there have been hundreds of thousands that have been used in hi-performance
applications. Through balancing these applications have performed admirably, but the fully counterweight
units are better designed to handle disbursement of load and twisting forces that each pair of
pistons & rods generate.
The counter-weight actually services two activities; one is to counter the offsetting weight from the
piston and rod assemblies but also to help dampen the torsional activity caused from the firing sequence
of the engine. But regardless of the number of counter-weights you must still dynamically balance both
types.
Let’s Get Started!
The first thing that we have to do is get the weight of all of the rotating and reciprocating parts. Using
the supplied Weight Scale System from our newest balance machine from CWT Industries, our Multi-Bal 5500 we start by weighing the Connecting Rods.
With this type of setup the weight values are directly sent to the computer software that allows the
us to log-in the weight of the part plus add the part number and description for later recall.
The rest of the parts (Pistons, Pins, Rings, Bearing etc.) are logged-in the same way giving us
a targeted Bob-Weight. We will then attach precision weights to the “Moment-Matched”
Bob-Weight bodies and mount them on the Crankshaft using a special alignment tool to perfectly place each bob-weight to an exact location.
The Crank Assembly description is logged into the computer and the system is ready to be spun.
It takes about 20 seconds for the machine to determine both the position and magnitude of unbalance
and display the data for us.
This particular example shows the left side unbalance @ 1.31 Oz-in and the right side @ 1.78 Oz-in. It
also is telling us to remove 10.68 grams of weight from the outside edge of the crankshaft or to drill it by using a 1” drill at a depth of .130 of an inch at the TDC Point.
The right will require .170 of an inch when the crankshaft is rotated to the assigned TDC Point on the
right side of the screen.
After these corrections were made the machine reported the following results.
Notice that the magnitude of unbalance force has been reduced to 0.01 for both sides and that the
position of any residual unbalance is equally opposed from the right and left side (180 degree). This
crankshaft assembly is correctly balanced.
As you can see the process is made very simple through the help of advanced technology with our Multi-Bal 5500 HMVF the entire process can be done quickly and accurately. One key feature that is embedded into our method of balancing is a process defined as “Third Plane Analysis”. This advanced feature is superior to 2 plane or some times call plane separation machines that others use.
In both previous visual examples (Camshaft and Crankshaft) you may notice that the unbalance forces we not opposed from each other. When this particular event takes place the 2 plane balancers have limited abilities to truly identify magnitude and position of the unbalance, they get close if the disparity in magnitude between each other are reasonably close. But when you have large amounts of weight differences and non-offsetting of the unbalance position, they become confused and misreport.
Others have had to learn to lower the weight on each side in small increments while noticing that the position and magnitude on the opposite side of the crankshaft were being simultaneously effected.
Eventually they would get the unit balanced to tolerance and in some cases the crankshaft would look like “Swiss Cheese”. All of this is a direct result of the technician having to chase the unbalance due to misreporting by the machine.
Our Multi-Bal 5500 series Software and Hardware are able to recognize the “Out of Couple” and “Differential of Magnitude” environment and through the proprietary software algorithms the collective forces of the left plane and right plane are properly analyzed showing how these forces can work in concert to generate a third plane. This activity is what disrupts the reporting ability of 2 plane or plane separation style balancing machines.