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Head Bolt Torque Specs

cylinder head

Other than an overhaul, the most comprehensive disassembly job that can be done to a vehicle is removal of the cylinder heads. This requires an almost total breakdown of the engine itself and once accomplished, of course, everything must be replaced again.

When the cylinder heads are put on, they have a specific torque (pounds of pressure) requirement for the bolts as well as specific sequence of bolt tightening to be used to ensure that the heads are evenly seated onto the engine block.

The head bolt toque specs will vary according to the materials used to make the heads and block and the size of the heads themselves. Every engine manufacturer will have a specific set of torque specifications and tightening sequence for their products.

Typically, the aluminum heads on a modern vehicle will have 35-40 pounds of initial torque to tighten them. Cast iron heads will have specs in the 50 pound area. Both are then usually followed by a tightening sequence that goes from the center-most bolts outward radially and that are measured in quarter or half turns rather than torque (psi).

Because the engine block and heads expand and contract with heat (as does anything made of metal), these torque specifications are meant to keep the metal pieces together during contraction (cooling) without producing gaps where coolant or oil can mix as well as to provide for the expansion without causing cracking or breaking in the parts themselves.

This necessitates tight tolerances when torquing bolts into place to hold the heads to the block.

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