Backlash

If you were to put a torque on the gear in 1 direction so one side of the teeth on one gear are in contact with one side of the teeth on the other gear, then changed the torque so the opposite sides of the gear came into contact, that distance that the gear teeth traveled before contacting the opposite side is the gear backlash.  You can measure it also by degrees of rotation or the change in length of a string wrapped around the shaft that a gear is attached to, just takes some geometry.  This link should take you to a good picture that shows it:

http://en.wikipedia.org/wiki/File:Backlash.svg

Hurst


Edited by Hurst - 21 Mar 2011 at 9:45am

You don't want to set gears with no backlash. The slightest amount of runout in either gear would add stress to the bearings carrying the assembly if the was no backlash. Yes you can feel the backlash.
 There should be a number of blind holes drilled in the tube that contains the bearings and shaft connected to the pulley. Engage the gears and lock the set screw , check backlash. If it is too much turn to the next hole, continue this till you get the right amount of backlash and then, make a chisel mark on the housing to line up with the mark on the frame. Use the mark as a reference if you remove the shaft for loader work etc.

you should have a little clunk-clunk but not much.wfmurry gives good advise. Don't know the spec but .010 at the gear could be 1/8in at the outer dia of pulley.