Question bout 2.9ltr. Headbolts?

[fenix1]

Been 3 weeks now since I worked on my 88 Bronco II. Managed to get the Heads off finally. Rounded up all the parts I need. I managed to break the heads off the Crossover Bolts. Grinded them down to the Exhaust Manifold. Also, grinded down 7 of the 12 Exhaust Manifold Bolts that broke. Had to take a punch and make a Starter Hole for my Drill Bit. Drilled them all out and took an Eez Out and backed them out. I live in the sticks and no one in the 2 little towns nearby had any bolts to fit. The Crossover Flange Bolts are 12mm.x1.25 and the Exhaust Manifold Bolts are 8mm.x1.25 in case anyone was wondering. Well, I decided to get some Heat Treated US Type Heat Treated Bolts and Drill and Tap the holes in the Exhaust Manifold and get away from the Metric since nobody seemed to know where I could get the originals. Finally to my question...Says to torque Head Bolts to 22ft.lbs. and then to 55. Then wait a few minutes and turn the Bolts 90*. Why don't they just say then torque to 70lbs. or something instead of 90*?

[rebocardo]

> Why don't they just say then torque to 70lbs. or something instead of 90*?

To evenly seat/compress the head gasket on all edges and to not warp the head. Things such as head bolts are frequently set that way because you are stretching the bolts just to about their yield point so they put a lot of pressure on the head and to make sure they do not loosen up from vibration and freq. heating up and cooling down. Which is why they can only be used once.

Many hub nuts are done in just about the same way with two torque adjustments and then backing them off/on a few degrees more.