The OCC team are back in Season 4 with more ingenious custom bikes as Paul Sr. and Pauly test the limits of their machines and each other in American Chopper Tool Box 10. The New York based OCC team go green, designing the worlds first renewable fuel chopper for Iowa Farm Bureau. Meanwhile Mikey and Sr. grill up a BBQ to celebrate the new OCC World Headquarters but the mood turns sour when one of the crew issue a shock resignation. Testing the crew's building skill, the next project see the OCC boys getting technical as HP and Intel put the latest robotic advancements into chopper design. Meanwhile Paul Sr. decides to call on the tattooists of hit Discovery series Miami Ink ... but will they be happy with the end result?