The left rear head bolt must be installed into the head prior to head installation. Coat the threads and heads of the head bolts with sealing compound (GM part #1052080 or equivalent) before installation. On 1988-95 models, tighten the head bolts in three stages: 20 ft. lbs. (25 Nm); 50 ft. lbs. (68 Nm) and finally, 1⁄4 or 90° turn more.
Fig. 10: Cylinder head bolt tightening sequence-6.5L engines