For all 1986-1989 Evolution Big Twin. Increases clutch area more than 325 percent. Upgrade the notoriously poor clutch of the 1986-1989 H-D Big Twin with Rivera Engineering's Pro-Clutch for early Evolution. Quick, easy installation (press out the OEM hub, press in the Pro-Clutch), a 325 percent increase in clutch area, and smooth, easy hand control make Pro-Clutch the best way to upgrade the existing stock style clutch. Sold as kit.