How to Change the Head Gasket on a 4.9 Straight Six

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The Ford 4.9-liter, 300 cubic-inch straight-six engine was based on the 240 cubic-inch six-cylinder and was the largest straight-six produced by Ford. The usual reasons for replacing a head gasket are either the need for a valve job, or a blown head gasket. If you have a blown head gasket be sure to have the head checked by a machinist, because it may need to be surfaced. If you have basic auto repair skills, you should be able to replace the head gasket in about six hours.

Things You'll Need

  • Drain pan
  • Flat-head screwdriver
  • Marker
  • Masking tape
  • Ratchet and socket set
  • Shop rags
  • Gasket scraper
  • Cardboard box
  • Assistant
  • Scotch Brite pad
  • Parts cleaner
  • Torque wrench
  • Gasket sealer
  • Park the vehicle on a level, paved surface and set the parking brake. Allow the engine to cool sufficiently so that you will not get burned when touching it.

  • Place a drain pan underneath the radiator drain valve. Open the valve drain the radiator. Be sure to close the valve when you are done. Use a flat-head screwdriver to loosen the upper radiator hose clamp at the thermostat. Pull the hose off of the thermostat housing.

  • Remove the air cleaner, unhook the throttle return spring from the carburetor, lift up the clip on the end of the throttle rod where it attaches to carburetor linkage pulled the rod out of the linkage. Don't lose the little clip. Pull the distributor vacuum advance those off of the carburetor. Pull the PVC valve and breather hose out of the valve cover. Use a slotted screwdriver to loosen the hose clamp on the fuel line at the carburetor. Remove the line.

  • Wrap a piece of masking tape around each of the spark plug wires and number them one through six, from front to back then remove the spark plug wires. Use a ratchet and spark plug socket to remove the spark plugs. Use a ratchet and socket to remove the valve cover bolts and valve cover. Remove the old valve cover gasket from the valve cover, remove any debris with a putty knife, spray some solvent on a shop rag and clean the gasket surface of the valve cover.

  • Use a ratchet and socket to loosen the rocker arm pivot nuts far enough so that you can turn the rocker arm to the side and pull out the push rod. As you remove the push rods, put a piece of masking tape with a number on each and put them back in the same order when you install the cylinder head.

  • Use a ratchet and socket to remove the two nuts from the exhaust pipe flange where it attaches to the exhaust manifold. Pull flange down off the studs on the exhaust manifold. Use a ratchet and socket to remove the nuts and bolts that hold the intake and exhaust manifolds onto the cylinder head.

  • Use a ratchet and socket to remove the 14 cylinder head bolts. To aid in reassembly, push the bolts into a piece of cardboard in rows, in the same order as you took them out of the cylinder head. One row for the bolts on the driver side of the engine, and one row for the passenger side. Write a number on the cardboard next to each bolt in the following order: Passenger side front to rear: "11-7-3-2-6-10-14," and driver side front to rear: "13-9-5-1-4-8-12." This number sequence will be used when you install and torque the head bolts.

  • Lift the cylinder head off of the engine block with the aid of an assistant. If the head gasket remain on the engine block, remove it. Place shop rags in each cylinder to catch debris that may fall in the cylinders when you clean the block. Carefully remove debris with a gasket scraper and clean the gasket surface on the engine block with a Scotch Brite pad.

  • Place the head gasket on the engine block with the proper side marked "Top" facing upward. Have your assistant help you lower the cylinder head onto the block. Remove the head bolts from the piece of cardboard and install them in their proper positions in the cylinder head.

  • Use a ratchet and socket to tighten the bolts into the cylinder head until they just start to get tight. Using your piece of cardboard is a guide, start with the first bolt and torque it to 40 foot-pounds. Torque the rest of the bolts in their proper numerical sequence. Moving in a crisscross pattern as you tighten. Set the torque wrench for 60 foot-pounds and repeat the sequence. Set the torque wrench for 75 foot-pounds to apply the final torque.

  • Install the push rods through the cylinder head in their proper positions. Position rocker arms so they are contacting the valve and push rod. Use a ratchet and socket to tighten the rocker arm pivot nuts just enough to remove the play between the push rod and rocker arm. Use a torque wrench to slowly tighten the pivot nuts to 15 foot-pounds.

  • Position the intake/exhaust manifold, with a new gasket, against the cylinder head and install the bolts and nuts finger tight. The intake and exhaust manifold has a torque pattern that must be followed, similar to the cylinder head. The upper row of fasteners has three nuts, the lower row is all bolts. The upper row is numbered "13-12-11-1-3-2-4" from front to rear, and the lower row is numbered "10-9-8-7-6-5." Tighten the bolts according to the pattern, torquing each to 15 foot-pounds, then 20 foot-pounds and finally 28 foot-pounds.

  • Reinstall the remaining parts in reverse order of their removal. Refill the radiator with coolant.

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References

  • "Haynes Ford Pick-Ups and Broncos 1973 through 1979"; Dennis Yamaguchi and J.H. Haynes;1983
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