Here are the steps to tighten the head bolts:
1. Clean the threads of the head bolts and in the cylinder block.
2. Apply a light coat of engine oil to the threads of the head bolts.
3. Insert the head bolts into the cylinder block.
4. Tighten the head bolts to 15 ft-lbs (20 Nm) in a criss-cross pattern.
5. Tighten the head bolts to 20 ft-lbs (27 Nm) in a criss-cross pattern.
Note: Do not over-tighten the head bolts, as this can damage the engine.