There is no Mech wrench.
You can get the Multi-tool from the Cantina when you arrive on the island.
The Mech Crank is at the far upper left on some vines, and can only be reached through the Living Quarters.
The Mech Motor is on a conveyor belt in the Greenhouse, part of the Production zone (Research Lab) at the far right of the island. Also there is the Living Quarters key that lets you reach the Mech Crank.
(see related question)
find the mech crank and mech battery
You have to get the mech crank and the motor.
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)
you go in it
in your bag there is a mech crank 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
In the garage next to Sully's shop
to the mech to attach it
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.
Along with the Mech Crank, it completes the Walking Mech that is in the garage next to Sully's. To get the Crank, you have to go through the Living Quarters to reach the high vine at upper left.
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.