 ENGINE BALANCING EXPLAINED
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Covered in This Article:
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Why Balance?
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What Components Break?
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What is Balancing?
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Special Procedures
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Costs
Do You Need to Purchase HEAVY METAL (no, not the music)?
We are regularly asked if we sell heavy metal for balancing purposes. No, we do not, but you can purchase it direct from CWT Industries by calling:
1-800-449-1849
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Engine balancing has a variety of benefits, but many people do not understand why it is necessary, or how it is done. This article will help educate and enlighten the reader on the benefits, procedures, and costs.
You might ask if the engine in your new car has been balanced. Yes, it has, but it has been done in a production environment. This process has been dramatically improved over the last decade, but it is still not as accurate as a trained machinist in a specialty balancing shop with the right equipment can perform. Improvements in materials, manufacturing, and production machining has improved the quality of OEM engines.
At Century Performance Center we are no longer performing maching or balancing. The information we have provided is here to assist you in finding the most power and reliability from your engine. This article is for education purposes to assist our current and future customers.
Why Balance Your Engine?
The first and most obvious benefits of balancing your Performance or Racing Engine is that of Horsepower and Longevity. Any automotive or marine engine spins at enough RPM (revolutions per minute) to cause damage to bearings, moving parts, and the cylinder walls if the engine's reciprocating assembly is not balanced correctly. You can even discount the damage comment and just consider how much harder the engine has to work to offset dynamic friction. Over time engine life is reduced, but day-to-day operation is less than optimal on an engine that is out of balance. This is not just about performance and racing applications. If you can reduce the rotational friction and forces working against the smooth motion of components in your engine you will increase performance (power and torque output), RPM capability, and extend engine life.
Just about everyone has been in a car or on bicycle with a wheel out of balance. The resulting feeling is often vibration, shimmies, and lack of complete control. Imagine this same vibration, now partially hidden within the confines of your engine. In some instances (extreme out of balance) you will see or feel the engine vibrations, but most cases of engine unbalance go unnoticed. These unseen or unfelt errors in the engine's rotating assembly is quickly causing the engine's demise.
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Balancing Your Engine Helps:
- Save on Fuel
- Reduces Friction (heat)
- Increase Longevity
- Increase Horsepower
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- More Consistency
- Smoother Operation
- Lower Chance of Fluid Leaks
- Lessens Component Failure
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What Happens With an Unbalanced or Incorrectly Balanced Engine?
Any engine that is not balanced or balanced incorrectly will hurt internal engine components. The chart below shows an example what a few grams of weight measured at 4" off center (imagine a 4.00" stroke crankshaft). The chart shows you the forces exerted at 4", and various engine RPM.
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OB Weight Measured @ 4"
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2000 RPM
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4000 RPM
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6000 RPM
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8000 RPM
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7 Grams
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7 lbs
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28 lbs
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63 lbs
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112 lbs
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14 Grams
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14 lbs
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56 lbs
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126 lbs
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224 lbs
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28 Grams
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28 lbs
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112 lbs
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252 lbs
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448 lbs
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The engine is a unique device. Being able to sustain the speeds in which the internal parts reciprocate is a feat within itself. The stress loads, the friction, the heat all are trying to tear the engine apart. The smoother the engine runs, the less these negatives have an effect. The internal combustion engine is a "dirty" mechanical device, or should I say an inefficient power supply. This is due to the "Friction". Any way to release this friction, to limit it, will offer gain in the benefits described above.
The parts most affected by this inept balancing are the ones that the engine needs the most to survive.
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Piston Rings ... fail to seal
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Bearings ... early and irregular wear on connecting rod and main bearings
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Damper ... the device that tries to assist in controlling harmonic shock gets overworked and begins to deteriorate.
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Oil Pumps ... Chatter and bounce, which can also create spark chatter and early ignition part failures (on oil pumps driven off same drive as distributor)
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Timing Sets ... Early chain stretching as chain has to make up for damper failures
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Valve Springs ... Valve instability, spring harmonic failures (worse with gear drives)
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Transmission ... Front Pump failures in automatics, early pressure plate and clutch spring failures
All these parts and their related components are affected. Those engines that have survived (I know they exist) are usually just a bit of luck. I've seen some survive nearly forever, but if one was to look close, there are factors which allow this. Usually the parts are close if not nearly exact from the start or else there are other "countering" factors which do a sort of "self balance". Do not count on these "gifts", they aren't predictable or standard.
What is Balancing?
Balancing is the action of matching the weights of the reciprocating parts of the engine. These parts include, but are not limited to:
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Pistons and Piston Pins
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Piston Rings
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Rod Bearings
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Connecting Rods (large and small ends)
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Crankshaft
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Damper (harmonic balancer)
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Flywheel/Flex Plate
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Pressure Plate/Clutch
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Also, an "Estimated" Weight of Oil is part of the calculations
Once you have these parts together, the process of Balancing the parts goes as follows:
First, the individual parts are weight matched. These include the pistons, rods and rings. There is not much you can do to the rings or rod bearings so, other than just setting up the "File-Fit" rings before balancing, all you do is supply a single set for one piston (3-piece oil ring, second ring, top ing) to the shop doing your balancing. First all of the pistons are weighed, then all the rods, locating the lightest of each. At that point, if you are reducing the weight of these items, machining the lightest of each component first. You now match weight of the pistons and rods.
| NOTE: "All" other component machining must be done BEFORE balancing is attempted...! |
The RODS are matched as "small ends" and "big ends". This means you match all the "big ends" by hanging on a special hanging fixture, then you do the same with the small ends. Be sure to double-check!
The PISTONS are also weight-matched, but the "material removal" machining is done either under the piston pin boss with a special offset cutter, or it is done by drilling holes (very carefully) on the surface of the pin boss. You do this to both piston bosses, sharing the material loss. You DO NOT want to remove the material off only one side.
The Damper, Flywheel/Flexplate, Pressure Plate, etc. are individually spin balanced. Just like the wheels and tires on your car.
After you have completed this weight matching, you are now ready to mount the Crankshaft in a special Balancing Machine that spins the Crank with the Damper and Flywheel installed, as well as "Bobweights" that duplicate the compiled weight of the Pistons, Pins, Rods, Rings, Bearings, and a calculated "weight of oil". The crank is usually mounted in Teflon or Nylon "V-Blocks" on the Balancing Machine. The Balancing Machine measures "out-of-balance" through Computer-Controlled sensors. Just like the way your wheels are balanced when you have tires installed (or hopefully during normal maintenance as well), yet the engine balancing machine is much more accurate.
Any errors in the balance of the crank is corrected by either:
The Balancing Machine in many cases has a Milling Machine built on to it, making quick removal of material. The Milling occurs on the crank's counterbalances. If metal (weight) needs to be added, it in most cases is done within the existing balance holes in the crank. In other cases directly to surface of counterweights. In only extreme cases, typically with very lightweight design crankshafts, is Mallory Metal used.
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Special Balancing Processes
The most common special Balancing Process includes the addition of Mallory Metal to the crankshaft. Mallory Metal is an extremely heavy metal used in extreme "out of balance" situations or when using ultra light crankshafts, whereas normal welding material weight is not enough weight to correct imbalance. Other uses is in certain racing applications there is the need to "neutral balance" the crank. This is usually done when no damper is used, as in the Alcohol Burning Sprint Cars classes. Mallory Metal is quite expensive and it is only used as necessary.
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Costs
I must first state that the cost of balancing will always be outweighed (oops, a PUN) by the benefits of the process. A typical machine shop is charging between $120.00 to $140.00. (This includes all the above described steps, but does not include the installation or cost of mallory metal).
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