GT3235 belt problem
 

I noticed that one of my belts that turn the crank pulley hooked to the mower deck driveshaft had slipped off. When I put it back on I seen where the spring tensioner looked weird. There is a flat piece of metal that looks like its riveted on was loose. Looks to be riveted in 2 places. Well 1 rivet is missing and the flat metal piece has fell on a pulley. Any idea what this flat piece of metal is for? Motor is a 25HP Kohler Command on a '01 CC GT3235. Any place I can find a front engine layout that shows how the belt system works?