T-T-Y (TORQUE-TO-YIELD) HEAD BOLTS
T-T-Y head bolts are engineered to stretch within a controlled yield zone. Once they reach this zone they spring back to provide a precise level of clamping force. This stretches the bolts into their elastic range. In some cases the stretching approaches the bolts’ elastic limit, permanently stretching them. Reusing stretched T-T-Y head bolts can cause improper or uneven torque, damaged engine threads, and broken bolts, any of which could lead to head gasket failure. It is important to use new bolts and proper torquing procedures during reassembly.
Torque specifications are available at www.fme-cat.com
or downloadable in a pdf format at www.felpro-only.com
When a Torque-To-Yield bolts are installed, they are first tightened to a specified torque rating. Then the bolts are turned by a specific number of degrees, which stretches the bolts into their yield zone.