Engine Balancing

Why Balance Your Engine?

The first considerations 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 cylinder walls if the engine's reciprocating assembly is not balanced correctly.

Just about everyone has had a car or bicycle with a wheel out of balance. The resulting feeling is often vibration, shimmies, and lack of complete control. Imagine this feeling, now partially hidden within the confines of your engine. In many 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 assembly is quickly causing it's demise.

Balancing your engine helps:

  • Save on Fuel
  • Reduces Friction (heat)
  • Increase Longevity
  • Increase Horsepower More Consistency
  • Smoother Operation
  • Lower Chance of Fluid Leaks
  • Lessens Component Failure

What Incorrect Balancing Does

Any engine that is not balanced or balanced incorrectly will hurt internal engine components.

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.

  • Piston Rings ... fail to seal
  • Bearings ... early and irregular wear on connecting rod and main bearings
  • Damper ... the device that tries to assist in controlling harmonic shock gets overworked and begins to deteriorate.
  • Oil Pumps ... Chatter and bounce, which can also create spark chatter and early ignition part failures (oil pumps driven off same drive as distributor)
  • Timing Sets ... Early chain stretching as chain has to make up for damper failures
  • Valve Springs ... Valve instability, spring harmonic failures (worse with gear drives)
  • 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 weights of the reciprocating parts of the engine. These parts include, but are not limited to:

  • Pistons and Piston Pins
  • Piston Rings
  • Rod Bearings
  • Connecting Rods (large and small ends)
  • Crankshaft
  • Damper (harmonic balancer)
  • Flywheel/Flex plate
  • Pressure Plate/Clutch
  • "Estimated" Weight of oil

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" to the shop doing your balancing. You first weigh all the pistons and all the rods, locating the lightest of each. At that point, if you are reducing weight of these items, do it first to the lightest parts. You now match weight of the pistons and rods.

NOTE: "All" other 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:

  • Drilling to remove weight
  • Welding to add weight
  • Machining and Adding "Heavy Metal" (Mallory Metal)

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.

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.

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 $180.00 to $290.00. (This includes all the above described steps, but does not include the installation or cost of mallory metal).