Final answer:
Torque-to-yield head bolts do not permanently stretch when they are torqued. They must be torqued in a proper sequence and are usually tightened to a specific torque then rotated tighter. Many older engines have torque-to-yield bolts.
Step-by-step explanation:
No, torque-to-yield head bolts do not permanently stretch when they are torqued. Instead, they are designed to stretch elastically and return to their original shape when the torque is released. This stretching helps to achieve a more consistent clamping force on the cylinder head.
Torque-to-yield head bolts must be torqued in a proper sequence to ensure even distribution of the clamping force. This helps to prevent leaks and maintain the integrity of the cylinder head gasket.
While many older engines do use torque-to-yield head bolts, newer engine designs often use other methods of fastening, such as stretch bolts or torque angle bolts.
Finally, torque-to-yield head bolts are usually tightened to a specific torque, and then rotated a certain number of degrees tighter to achieve the desired clamping force. This helps to ensure a consistent and accurate torque value.