The reason for the two times at 8.7ft lbs is as you make your round tightening the bolts some pressure is taken off the ones you started at as the gasket crushes and more bolts are taking the load(The first ones you did, may loosen up). The second pass brings them all to an equal torque of 8.7ft lbs.
Final torque is 12N.m(8.7ft lbs)
Final torque is 12N.m(8.7ft lbs)
