When I was doing some research on the FJ-09/FZ-09, I saw numerous threads regarding appropriate amount of chain slack and that the figure in the owners manual was probably wrong. The amount of slack, and whether it's measured with the bike on the side of center stand isn't trivial. The amount of slack changes when the swing arm moves. The center of the countershaft sprocket is in a different place than the swingarm pivot. Slack is at its minimum when the swingarm is parallel to the ground and at its maximum with the bike on the center stand with it hanging down. If there is insufficient slack there will be very high loads placed on the countershaft and swingarm bearings when the suspension is compressed. 1/2" is probably okay when slack is at its minimum, but not with the bike on its side or center stand.