SR 500 crank balancing 

This video may show the basics for professional dynamic balance equipment. But myself being no professional I am still in the learning phase. I did a few Yamaha SR 500 crankshafts , time no factor for me at home for exercises on my test rig. Forged or cast crank webs very often are way off limits so dynamic balancing will reduce a lot of the roughness of the engine. I fabricated a calculated balance weight for the SR crank that is fixed with Loctite on an undersize crank pin. The lot is assembled with low strength Loctite 222 or 221 so you can true up the crank and easily disassemble after balancing .
The procedure is to spin up the crank , no weights attached, as high as you dare. The instrument takes its results from two g-sensors . Then you add a specified weight, here a 7.90 gram magnet I had, to the left web, entered in the electronics, diameter of webs as well. This second run will produce new numbers of course. The third run has the magnet on the second web and numbers recorded in the electronics. Three runs will tell the equipment how the test object behaves and you get calculated positions for both webs for adding weights or drilling holes on opposite places to achieve minimal vibration at high revs.
When balancing cranks you will not want to drill at any place the electronics tell you so you will have to compensate this by some trial and error . That is why I first use a collection of magnets to see what I can do and then deciding on positions for actually drilling holes . This crank was not the worst I had but you can see how much drilling was required for perfect smoothness.