These pulleys are the mechanical gear that adjusts the inlet cam on a JZ Vvti engine. 
 
With age these pulleys are failing more and more, leaking and worse dropping enough oil pressure that the vvti system can not function correctly.
 
These are a non serviceable item inline with the toyota service guide and despite some services kits being available it's not something we would ever recommend due to the laser alignment of the backlash.