Cylinder Head Bolts
High-strength fasteners that secure the cylinder head to the engine block, compressing the head gasket.
Cylinder head bolts are high-tensile fasteners that clamp the cylinder head tightly onto the engine block, compressing the head gasket to seal the combustion chambers and oil/coolant passages. Because of the extreme pressures generated by combustion, these bolts must hold thousands of pounds of clamping force.
Most modern engines use Torque-to-Yield (TTY) head bolts. These bolts are designed to be stretched beyond their elastic limit during installation, providing a highly uniform clamping force. Because TTY bolts stretch permanently, they are 'one-time use only' fasteners and must always be replaced with new ones during a head gasket repair.
If head bolts are reused or improperly torqued, they can stretch further or fail to provide enough clamping force, leading to head gasket failure and engine overheating. Mechanics follow strict manufacturer torque specifications and sequences (using a torque wrench and angle gauge) to tighten head bolts.