I've got a 4.2 liter 97-F150. I pulled the head yesterday. After reading the manual (Hayes) it said to disgard the old head bolts and install new ones. Do I really need to do that? It also says that about the intake manifold bolts.

 

DO NOT use the old bolts! Head bolts in modern engines employ "torque-to-yield" technology that stretches the bolts a predermined amount just within the yield tension limits in order to provide long-term uniform clamping pressure. The scheme also gives more even tension from bolt-to-bolt than using the conventional torquing method where tension can vary widely dependent upon the friction variability from bolt to bolt.

("Torque-to-yield" is used throughout the main engine systems on the Space Shuttle in order to use 90 percent of the ultimate strength of each fastener. The fasteners can be lighter since the ultimate tension can be accurately determined by the stretch method. An ultrasonic transducer is fitted to the head of the bolt and the stretched length is measured by reflected sound as the bolt is torqued. Lighter fasteners throughout the assembly reduces the total system weight by a significant factor....less engine weight = more payload weight.)

When you get at the replacement of the heads you will need all the grunt you can get to put that final 90-degree turn on each bolt in sequence.

A 24 inch breaker bar will come in very handy for you.

 

1997 4.2l v6:
Why the need to back the head bolts right off after tightening them in 3 stages to ~30 Lbs-Ft before doing the final tightening sequence??

The info I find for the '97 4.2L says to give them ~ 180 degrees, not 90 degrees, after getting them back up to 35 Foot Pounds?