Here's why:
* Torque-to-yield bolts: Head bolts on most engines, including this one, are torque-to-yield. This means they are stretched to a specific yield point during tightening. Once stretched, their clamping force is diminished. Reusing them risks insufficient clamping pressure, leading to a head gasket failure again, or other issues like warped heads.
* Material fatigue: The bolts may have experienced micro-fractures during their initial tightening, even if they weren't visibly damaged. Reusing them increases the risk of failure under the stress of engine operation.
* Peace of mind: The cost of replacement head bolts is relatively small compared to the labor and potential damage from a head gasket failure. Replacing them provides much greater assurance of a successful repair.
In short, while you *might* get away with reusing them, the risk of a repeat failure isn't worth it. The cost of new bolts is a small price to pay for a reliable repair. Consult a repair manual for the proper torque sequence and specifications for your engine.
