Re: Cylinder head bolts
Surface rust on the head of a bolt is not a problem unless it becomes too worn for a six point socket to hold.
Clamping force of a head bolt is determined by BOTH the torque on the thread AND the grade of the bolt in that the grade determines the amount of 'stretch' that occurs in the bolt at the rated torque.
Changing bolt material which is NOT of the same grade will also change the clamping force, that can lead to a problem holding a head gasket and may not be recommended.
Clean the existing bolts then inspect to ensure serviceability, if poor then replace with OEM equivalent to ensure the clamping force on the head gasket remains adequate. Clean and paint after assembly to minimize any further rusting.
Lightly oil threads and underside of head during assembly to ensure proper torque during tightening is not obscured by thread friction.
