What Is the Tightening Sequence on a 4.3L Engine?by Mike Aguilar
When rebuilding your GM vehicle's 4.3-liter engine, certain engine parts must be tightened in a specific pattern and to specific torque values. Three of the most significant parts that require specific patterns and values are the intake and exhaust manifolds and the cylinder head.
Cylinder Head Torque Sequence
The 4.3L GM motor has 13 head bolts. The upper seven bolts are numbered from front to rear---under the valve covers---as 12, 8, 4, 5, 1, 9 and 13, while the lower bolts are numbered 11, 7, 3, 2, 6 and 10. The bolt numbering is the sequence in which they should be tightened. The first time around, torque these bolts to 25 foot-pounds, then move up to 45 foot-pounds and finally 65 foot-pounds.
The intake manifold has 12 bolts that must be torqued in two steps with different sequences. Both steps require a torque setting of 35 foot-pounds. The bolt numbering for the initial torque is 8, 1, 9, 10, 11 and 12 on the passenger side and 2, 3, 4, 5, 6 and 7 on the driver side. The final torque should go around the manifold counterclockwise starting at the driver's side front of the manifold.
Accepted practice in the automotive industry when installing exhaust manifolds is to start in the middle and the work to both ends. This prevents manifold warp. These bolts must be torqued to 33 foot-pounds.
Mike Aguilar is a freelance writer with over 30 years of professional experience as a mechanic and over 10 years experience in the construction and home-improvement fields. He also attended an electrical apprenticeship for two years in Santa Clara, Calif., becoming a licensed low-voltage technician.