Every time a cylinder head is removed for the purpose of replacing the head gasket, the cylinder head bolts must be replaced. This is because head bolts are designed to stretch a certain amount under the original specified torque to ensure a proper head gasket seal around the cylinder head and engine block. Once a cylinder head has been removed, the bolts have likely stretched as much as they can and will not provide the necessary clamp load when reinstalled, which can lead to a head gasket failure and engine damage.
In addition, removing and reinstalling cylinder head bolts can distort their threads, making them unsafe for reuse. It is also worth noting that many modern cylinder head bolts are made from a special material that is prone to fatigue over time, so reusing them can increase the risk of bolt failure.
To ensure a proper and reliable head gasket seal, it is always recommended to replace head bolts anytime the cylinder head is removed.
