The CTA Manufacturing GM Lower Timing Gear Retainer Wedge, No. 7459, is designed to keep the lower timing gear retainer locked while the cylinder head is removed from engine. The tool services I4, I5, and I6 engines found in Buick, Chevrolet, GMC, Hummer, Isuzu, Oldsmobile, and Saab. Without this tool, the disassembly of the lower portion of the engine will increase labor time by 12+ hours for cylinder head repair, the company says. Make sure to follow the GM Service Bulletin 06-06-01-17C for using the Lower Timing Gear Retainer Tool. Failure to do so may lead to damage and additional repair steps not covered by the warranty.