If you think sometimes you have "bad vibes," imagine if you were a high performance internal combustion engine.  Harmonics, "bad vibes," although seldom recognized, exist in every internal combustion engine. There is a good side and a bad side to every thought.  Your engine only knows the bad side; most of the time it has bad vibes.

     Let me attempt to explain.  The bad vibes  (and all are) come from crankshaft twist/rebound.  Simply put, each time that the air/fuel mixture is ignited within the engine’s cylinders, the combustion causes an extreme amount of cylinder pressure. This cylinder pressure is applied to the pistons and then to the connecting rods and is transferred to the crankshaft.  This downward force makes the crankshaft turn.  Because this pressure is so great, it produces a torsion vibration from the pistons and incorporated with the crankshaft vibrations, causes the crankshaft to twist and deflect causing an action referred to as "tortional harmonic vibration."

     If this vibration is not controlled, and it can be to a degree, premature main bearing wear and possibly main journal wear on your crankshaft can occur.  This can even cause crankshaft breakage.  Harmonic vibration can be controlled by a vibration damper (a harmonic damper).  Many times this is referred to as a harmonic balancer.  Don’t be confused by the phrase “harmonic balancer.”  The damper is to control harmonic vibrations, not necessarily to balance the engine’s rotating assembly.  The balanced rotating assembly depends on the crankshaft.  Some engines are balanced internally and some are balanced externally.  Internally balanced engines have all the counterweights located on the crankshaft.  Externally balanced engines have some of the required counterweight located on each end of the crankshaft, either on the flywheel/flexplate, vibration damper, or both.  This doesn’t mean that the damper has the proper amount of weight to bring the crankshaft to tolerance, it just means that the damper has enough counterweight needed to counter-balance the weight of the pistons and rods.  You would still want to have your engine’s rotating assembly balanced.

     The harmonics I referred to above can occur over a broad range of engine rpms.  There is a damper for your specific engine’s needs.  Stock-type dampers are tuned to control a narrow rpm range of your engine’s usage.  A performance engine can have a wide rpm band that requires critical harmonic vibration control.  Therefore, a performance engine requires an efficiently constructed damper.  This damper can reduce vibrations throughout a wider rpm range and will be constructed to handle a higher rpm range without self-destructing.  As I have mentioned, if this vibration is not controlled, it can be destructive to your engine.

     The vibrations that occur in your engine are not just a threat to engine failure caused by metal fatigue, they are torque and horsepower robbers.  If you can reduce engine vibration, you can eliminate power robbing effects such as spark scatter and you can improve valve timing accuracy.  Think about it for a second, if the crankshaft is vibrating, it is transferred through the timing set (timing chain, timing belt, gear drive) to the camshaft, to the rocker arms, to the valves.  As you can see, one major part of an engine affects almost every part of your engine.  One bad apple ruins the whole barrel so to speak.

     Now that you have decided on your engine’s needs (street, strip, race), it is time to select a damper for your engine.  In aftermarket replacement, the choices of dampers vary by manufacturer and by the material used.  Most manufacturers make a damper that is an OEM replacement.  Although they are referred to as OEM replacements, they are superior to stock dampers.  The aftermarket dampers are constructed from ductile iron instead of cast iron.  These dampers are ideal for a stock engine, but for a hi-performance engine with major modifications  that will be operating at much higher rpms than a stock engine, you would want to step up to a steel damper.  Most manufacturers of dampers make quality and affordable steel dampers.  These dampers are usually SFI rated.  This means that the manufacturer has tested the damper and it has been certified to handle high rpms and it is safe for these higher rpms.  Another popular damper for hi-performance and race engines is the fluid filled.  These dampers use an inertia ring and a thin film of high-viscosity silicone fluid inside of a steel damper to control those bad vibes.   Regardless of which damper you choose, if it is correct for your engine, it will do its job--just some dampers do it better.

     With the damper selected, it is time for installation.  The correct way to install a damper is with a damper installation tool.  Now that you  have selected a quality damper, don't damage it by using a carpenter's tool (a hammer) to install it.  Severe damage can occur during installation with such a device (a hammer).  This instrument (a hammer) continually applied to your damper (beating on it) can cause the inner hub to move at a separate rate onto the crank as opposed to the outer ring.  This can damage the elastic rubber in between the two parts on a steel or ductile iron damper, and definitely not improve the ability of a fluid filled damper.  A quality damper will be tight on the crankshaft snout, therefore it will be almost a press fit, hence the need for an installation tool.  This is an inexpensive tool to use with a quality damper on a hi-performance engine.  Along with this quality damper, another item sometimes overlooked is a quality, properly torqued new crank bolt.   This will keep the properly installed, quality damper where it is supposed to be--on the crankshaft.  

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