Quote:
Originally posted by JKWright
I never saw the thread on this subject, but I'd be hesitant to yank the balance shafts out of the QR if your car is a daily driver that you envision yourself driving a few years down the road. Unless your Altima is an all-out drag car, why take the risk of watching your engine vibrate its way out of the bay at 6000 rpm for a few horsepower?
The QR is a big, highly undersquare four cylinder with an 89 mm bore and a 100 mm (!) stroke. Such a design inherently lends itself to wicked second-order vibrations, which is why Nissan decided to equip it with two balance shafts, a first in its U.S. lineup. Removing them initially may not hurt anything other than the fillings in your teeth, but as the miles pile up the added vibration will be tough on journals, bearings and the like. Not good, methinks.
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Balance shafts just cancel the second order natural up and down moment that all I-4 motors exhibit. The vibration that kills the motor is the torsional stuff that twists the crank and stresses the motors internal componets. The QR is an internaly balanced engine and removing the balance shafts does not affect this.
In fact if you have a highly moddifed QR, it is important to remove the balance shafts as seizing the shafts is one of the engines frist failure points. The balance shafts also create a great deal of crank windage and can contribute to oil control problems. Removing the balance shafts improves oil pressure and volume to the bearings as well.
On a QR removing the shafts results in a barily perceptable increse in vibration, the motor is still smoother than a KA24 and nearly as smooth as an SR20. As far as durabilty, Dave Colemans Pro-Rally QR has yet to suffer an engine problem in that punishing abuse of an engine.
The World Challange motor that Sunbelt Racing built has its balance shafts removed. It is common to remove the blance shafts on the Honda H22 and Mitsubishi 4G63 to improve reliablity and oiling on these motors as well.
Mike