CRJ-900 Maintenance Technician reported they discovered an engine mount bolt was installed without a bushing.

Narrative

AC 133 LH Engine FWD LWR Mount Bolt missing BushingAircraft was scheduled to have the LH Engine replaced. While we were removing the LH Engine we discovered that there was no bushing installed on the FWD LWR Mount Bolt.Not sure what all caused this; but complacency was probably a factor involved because a tech and an inspector both missed seeing that there wasn't a bushing on the bolt.We finished getting the Engine removed from the plane and on the ground. We inspected the hardware and mount and then proceeded to look for reference material for what to do before moving forward with installing the new engine. We were unable to find any reference material and moved forward with filling out a damage report.Not sure what to suggest here...