Hard to say what makes a bad motor unless you can see and hear it running. Noisy timing chain in the 4G54 2.6 is indicative of a motor that hasn't been well maintained, they are prone to issues with jet valves in the head and the Mikuni carb gets a fair amount of hate (normally from being waaay overdue for a rebuild). Noisy hydraulic tappets can sometimes be cured by performing an engine flush during a service. The blocks and bottom ends of them are near bomb proof and seem to survive nearly all levels of neglect and abuse. The only weak point in the bottom ends are from balance shaft failures due to excessive bearing wear. Other than the aforementioned comments they are like any other engine.