Season 4

Senior proposes that he and Junior combine forces to build a bike for charity, but Junior is unsure how to respond. But when Rick's wedding brings the two together, Junior gets the reassurance he needs to make a decision once and for all.

Senior and Junior brainstorm bike styles for their upcoming collaboration and decide to recreate the first bike they ever built together. Then PJD unveils the Geico Armed Forces tribute bike and OCC reveals the Cafe bike at the opening of the OCC Cafe.

Senior and Junior get to work on their bike build, which reaps surprising results as the two bond over old memories. Meanwhile, PJD starts a trike for Loopster while OCC builds a bike to benefit Senior's favorite charity.

Senior and Junior bond during their bike build; OCC begins working on a bike for Wildgame Innovations; PJD reveals a five-wheeled trike for Loopster.

PJD begins a build for QUBX while OCC unveils a bike for Wildgame Innovations; father and son continue their collaboration.

OCC begins a build for the Sturgis Motorcycle Rally; PJD unveils a bike that was built for a technology company; and Senior and Junior complete their bike build.

Senior receives a stern, on-air lecture from a late night celebrity, Junior launches a new business venture and Senior visits PJD for the first time ever. Then at Sturgis, Senior rides side by side with a bike industry icon.

Junior and Senior discuss potential future business collaborations; PJD finishes a bike for RoadLoK, and OCC begins a super-bike build.

Senior and Junior start brainstorming the production bike, but the road is rocky from the start. First, the two bump heads when discussing design workflow. Then, when Junior leaves town, Senior hijacks control of the project.

Senior makes business decisions without Junior's approval; PJD and OCC unveil projects.

Junior and Senior disagree on the production bike design process.

When hurricane Sandy hits, the PJD crew rushes off to rescue the 9/11 Memorial bike. Progress on the production bike stalls out when Sr. and Jr. disagree on a plan of action. Sr. and Vinnie finally face off about their past differences after five years.

PJD's 911 Memorial Bike is in more hot water than they thought. The pranks leading up to Chopper Live rev up and Sr. and Jr. hit a snag when the production bike discussions open old wounds.

In the series finale, the crews are under pressure to finish the 911, GAF and Venetian bikes. Cody goes after OCC with a revengeful prank as Chopper Live draws near. Sr and Jr find common ground in their relationship but are at odds over the new company.

Senior, Junior and Mikey make a lasting impression by donating the TEUTUL Bike. Senior pulls one last prank and the threesome takes a raucous ride through the most dramatic and defining moments of American Chopper.

This is the final episode of the series. Mike Teutal appears in this episode and reunites with his father.