The only way to get the Mech Crank (atop some vines at far upperleft) is to use the Living Quarters key, which is in the ResearchLab at the far right of the island (essentially solving more thantwo-thirds of the quest).
(see related solution)
Poptropica Help Blog Steamworks Island
To get the crank, you have to first get the 'Living Quarters'key. This is on the far right of the island in the research lab,which is the Production Zone on the map. The Mech Motor is in thesame location. Once you have the key, you can unlock the LivingQuarters on the far left of the island (Gear Alley). In the LivingQuarters, find the way to Zack's room and solve the steam ventpuzzle. Exit at the upper left and cross the vine 'tightrope' toreach the crank.
Poptropica Cheats for Steamworks Island. This is the Hibernation Center, where all the residents of Steamworks have gone to sleep to avoid the plant monsters. Steamworks Island is an island of machinery wherein there’s a lot of puzzle to accomplish without the help of poptropica people because they are missing and that’s the mystery we are going to solve.
Go back to Sully's Garage and fix the mech machine.