You need to either check your existing head bolts to ensure that they are within tolerance, or better yet, replace them altogether. (The new bolts have a built in washer.)

These bolts are 'torque to yield', and thus get stressed into the plastic region of the stress / strain curve, which work hardens them. I was very nervous during the last 90 degree torque sequence on my head, and that was with new bolts installed.

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