It's usually a combination of the two depending on the specs specific to that vehicle.
in sequence torque bolts to 20nm, then again in sequence turn a futher 120 degrees, and again in sequence 120 degrees.
this is from a manual, but old head bolts might not take it:cylinder head retaining bolts torque (M12) stage 1 70nm stage 2 further tighten 90 degrees stage 3 further tighten 90 degrees cylinder head retaining bolts torque (M8) 25nmwrong. SeeHow_hard_is_it_to_change_the_head_gasket_yourself_on_a_1987_Mercedes_190e
3.4 litre cylinder head torque is 37 ft lbs +90 degrees
Oil bolt washers and threads lightly. stage 1: Torque all bolts to 30Nm stage 2: angle torque all bolts +90 degrees stage 3: angle torque all bolts +90 degrees
you don't have to have the head checked but its recommended. the head bolts are supposed to be torqued in counterclockwise order from the inside bolts to the outside bolts. torque them in order in three stages to 18 ft/lbs then to 27 ft/lbs then an additional 120 degrees except the front right stud which you torque to 90 degrees
20nm followed by 240 degrees personally i prefer 20nm then 2x 120 degrees to take the head bolts down nice and easy
Short bolts-46psi , long bolts- 43psi plus 90 degrees
Using new head bolts & lubing the threads tighten to 25Nm then a further 90 degrees+ another 90+ another 90+ 45 degrees.
first get new head bolts. they are torque to yield. torque them to 37 ft-lbs and then rotate an additional 120 degrees.
33ft.lbs then 90 degrees
36 ft lbs and then 90 degrees
40NM initially on all head bolts Then... 60 degrees on all Then another 60 degrees on all Then the M12x140mm bolts are a further 20 degrees