You need two parts : the Mech steam motor from the production zone, far right, and the Mech crank from the vine at the far left (top). The only way to reach the crank is to enter the living quarters. The key is also in the production zone, in a closet behind the carnivorous plant. (Before going to the zone, you also need the rubber mallet from the junk bin in Sully's.)
find the mech crank and mech battery
You have to get the mech crank and the motor.
Take it to the vine spot and click space bar to cut the vines. (it is to the left)
you go in it
The unfinished Mech that Zack was working on is in the garage next to Sully's. You need the Mech Motor and Mech Crank to finish it.In the garage next to sully's shop on the left side of the island.
pound it with the mech's weed whacker
The Mech Walker is the key to entering the storeroom and defeating the monster plants that are active there. Once you finish the Mech with the Motor and Crank, you can attach the Weed Whacker attachment and enter the door at the far left of the island.
You find the pie.
Go left along the vine and pick up the Mech Crank. Along with the Mech Motor you recovered from the Production Zone, use it to finish building the Mech walker.
You can get the mech crank at living quarters in Zack's room ( go up the ladder and exit the room and walk across the vine and pick up the mech crank)
Easy! Duck like you normally would! Point your arrow down.
You cannot, as it will not jump high enough to get to Main Street again. Thus, you cannot get to the blimp.