How to Torque a Cylinder Head

An engine's cylinder head seals off the engine head from the block, which contains internal combustion gases. The mating surface between the two engine parts must form a flat, tight seal. An asbestos or metal gasket separates the two. For the mating surface to be exact, a torquing pressure and sequence must be performed. A cylinder head that has been tightened down without the proper torque or sequence runs the chance of warping prematurely, allowing the gasket to fail or the head to leak at the outer seam.

Things You'll Need

  • Sockets and socket wrench (1/2-inch drive size)
  • Torque wrench (foot-pound design)
  • Carburetor cleaner
  • Grease (high-temperature)
  • rags
  • Owner's engine manual
  • Wire brush

Head Torque Procedure

  • Examine the head bolts carefully for any rust, stripped threads or heavy carbon build-up. If the block contains studs that protrude upward (instead of removable head bolts), examine the ends of the threads and look for any bent stud bolts. On either variety, the head bolt threads should appear sharp and well-defined. Replace any head bolts that appear cracked, or have threads that look like they have been worn or stretched.

  • Clean the head bolts thoroughly with carburetor cleaner and a wire brush. This removes all carbon and sludge from the threads and shafts. Spray carburetor cleaner into the bolt hole openings and use a coat hanger with a rag wrapped around the end to clean inside the opening. Remove as much grime as possible. Dry the inside of the bolt holes with a clean rag.

  • Place the new head gasket onto the block surface. Align the head to the surface, placing it over the small guide pins. Be careful not to slide the head back and forth over the new gasket.

    Dab the thread ends of each head bolt with high-temperature grease. Install the head bolts into their perspective holes, being careful to put the correct bolts in the correct depth holes. Do this by hand first, then gently tighten each one with the socket and wrench, starting in the middle and fanning outward. In the case of head bolt studs, run the head nuts down by finger and gently snug them with a socket and wrench.

  • Refer to your engine manual for the proper torque number. It will appear in a pounds-per-square-inch measurement. Take that torque number and divide it by a factor of three. For instance, if the head calls for 100 foot-pounds, you will have three numbers, starting with 33, then 66 and then 99. Set the torque wrench for 33-foot pounds if you have a "click" type torque wrench. If you have a needle, flex-type torque wrench, note the location of the 33-foot pound mark on the dial.

  • Follow the torque sequence (location) in the manual and tighten the first bolt or nut to 33-foot pounds. The bolt or nut will be in the center of the head. Follow the torque sequence for the rest of the bolts, tightening each one to 33-foot pounds. Reset the torque wrench for the 66-foot pound setting. Follow the sequence again, starting in the middle and fanning outward until you reach the ends. Reset the torque wrench again for the final setting, which will be 100-foot pounds.