X-Head DOHC Cylinder Guards ($189) cover 80 percent of the faces of the cylinder heads on 2010-12 BMW R1200 twin-cam engines. That’s critical, says, MachineartMoto, because, even in a driveway tip-over, the inertia generated by the fall will likely cause the bike to roll briefly onto the face of the head before settling down on its bottom edge. The injection-molded covers are made of a DuPont nylon polymer chosen for its unique blend of high-impact strength, resistance to changes in temperature and UV stabilization. A 7mm-thick thermoplastic rubber liner sandwiched between the cover and head further dissipates energy resulting from a hard knock. Stainless steel fasteners treated with Nyloc thread-locking compound hold the covers securely in place.