The 15,000-mile valve check is notorious on this engine. The manual guides you through removing the airbox, throttle bodies, and cam chain tensioner. It tells you which way to turn the crankshaft (clockwise only, via the 17mm plug on the alternator cover) to avoid bending valves.
: The Z900RS typically requires SAE 10W-40 oil (API SJ, JASO MA). A full oil change with a filter replacement generally uses approximately 4 quarts of synthetic oil. Kawasaki Z900rs Service Manual