On a relatively understressed near stock motor with bolt ons or low amounts of boost like what most of the people on this forum probably run, a solid pulley will not have any life threatening consiquences. The factory pulley with a 2mm (less than a 1/8th inch) damper is primarily there for wide band NVH (noise vibration harshness) supression from the engine and driveline. Removing the damper and replacing it with a solid pulley will lead to minor addtional NVH but will not harm the engine. In fact, most people claim their engines seem to run smoother with NST pulleys.
The engineering reasons are that most modern engines have a short, strong crank with, a relatively high natural frequency. The dangerous second harmonic that can cause damage occurs at an rpm that this sort of engine will never see, in the area above 10,000 rpm. Even the stock damper is not tuned for attinuation at this sort of rpm so the argument is somewhat of a moot point.
Now small engines that are pushing the limit with lots of revs, wimpy cranks, super long strokes, lots of boost and dwelling in the upper rpm ranges for long periods of time can benefit from a damper designed to deal with this sort of operation but our engine is not like this, and probably very few people with this motor on this forum push the envelope that hard. How many 2 Liter, 450HP, 11,000RPM motors do we have on these forums?
As far as I can tell, our engine has a strong and stiff bottom end that is well built for our intended use. It has a strong crankshaft which is less like to break due to torsional vibration.
There are a lot of Nissan guys who use underdrive crank pulleys in road racing series like NASA or SCCA. Road racing is much more punishing on an engine than other motorsports. The engine is subjected to run times lasting 20 to 45 minutes with the engine always in the upper ranges of its rpm limit. One race weekend is the equivlent of hundreds of 1/4 mile passes.
http://www.NonStopTuning.com sponsors the first ever wheel to wheel Scion tC NASA Road Race car. This car has been using underdrive pulleys from NST with great results since day one. They have also sponsored several cars participating in Fromula Drift. These cars have been using NST pulleys with no issues of any kind for the past few seasons. We could go on and on...
Is a solid crank pulley harmless to all engines? No it is not. Small, super high reving engines, when modified way past the simple bolt on stages may have problems. These engines reach critcal harmonics, past the 10,000 rpm range, an rpm often reached by certain race engines.
A mildly modded inline six will most likely be fine but one subjected to high rpm for long periods of time (90% of its life) with lots of boost will probably suffer. In this case , the stock balancer/damper is probably not adequate either.
Some of the older american V8 engines are externaly balanced and it is critical not to use a solid hub pulley not designed for these applications, or damage to the engine could result.
Our engines and most around here do not fall into the above catagories. Rest assured that your engines will not blow up and die or have a reduced life in street and even racing use with these parts.
I would bet that every "expert" that tells you otherwise has little personal, practical, real world experience with the subject.
