There is nothing in the event sheet to void the use of mousetraps without the spring. Are the students allowed use a disassembled mouse trap as a hinge without the spring attached?

All energy used to propel must be stored in non-metallic, elastic materials as per rule 3.a. Hardware like a metal hinge or metal pulley or similar is allowed provided rule 3.a is not violated. Metal parts must not provide energy to propel the vehicle.