GM Firebird 1967-1981 Repair Guide

Cylinder Head

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REMOVAL & INSTALLATION OHC 230 and 250 Engines



See Figure 1

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Fig. Fig. 1: When tightening the cylinder head bolts, make certain to follow the sequence shown all 230 and 250 engines


CAUTION
When draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

  1. Remove the air cleaner and drain the cooling system. Remove the thermostat housing with the hose attached, and position it out of the way.
  2.  
  3. Disconnect the accelerator pedal cable and the fuel and vacuum lines from the carburetor.
  4.  
  5. Disconnect the exhaust pipe from the carburetor.
  6.  
  7. Disconnect the exhaust pipe from the manifold then remove the manifold and carburetor as an assembly.
  8.  
  9. Loosen the accessory drive mounting bolts to provide slack in the timing belt.
  10.  
  11. Remove the timing belt rear lower cover, top front cover, and the support bracket for the upper front cover. Align the ignition timing marks (be sure that you use the correct illustration in Engine Performance And Tune-up ). Remove the timing belt.
  12.  
  13. Disconnect the spark plug wires.
  14.  
  15. Remove the rocker arms and the valve lash adjusters and tag them so that they can be returned to exactly the same location. Rocker arms are retained on the adjusters by spring clips.
  16.  
  17. Remove the cylinder head bolts, the cylinder head, and its gasket. The head should be placed on two blocks of wood to prevent any damage.
  18.  

To install:
  1. Before installing the cylinder head, the gasket surfaces on the head and on the block must be clean.
  2.  
  3. Apply sealer and place a new gasket over the dowel pins on the block.
  4.  
  5. Carefully lower the head into place on the block.
  6.  
  7. Install the bolts.
  8.  

The head bolts are of two different lengths and must be placed in the proper holes. When correctly installed, they will all rise an equal length from the head. Sealer must not be used on head bolts.

  1. The head bolts should be tightened in the proper sequence a little at a time with a torque wrench. Tighten the center bolts first, then the end bolts. All bolts should be tightened to a final value of 95 ft. lbs. To complete the installation, reverse the applicable steps of the removal procedures. Adjust the timing belt as outlined later in this section.
  2.  

OHV 230 and 250 Engines


CAUTION
When draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

  1. Drain the cooling system and remove air cleaner. Disconnect PCV hose.
  2.  
  3. Disconnect the accelerator pedal rod at the bell crank on the manifold, and fuel and vacuum lines at carburetor.
  4.  
  5. Disconnect the exhaust pipe at the manifold flange, then remove the manifold bolts and clamps. Remove the manifolds and carburetor as an assembly. There is a ring gasket at the exhaust manifold flange, and a gasket for each of the manifolds at the head. These will have to be replaced. On 1977 and later models with an integral intake manifold, remove the carburetor at the intake manifold, and remove the exhaust manifold.
  6.  
  7. Remove the fuel and vacuum line retaining clip from the water outlet. Then, disconnect the wire harness from the heat sending unit and coil, leaving the harness clear of the clips on the rocker arm cover.
  8.  
  9. Disconnect the radiator hose at the water outlet housing and the negative battery strap at the cylinder head.
  10.  
  11. Number the spark plug wires, then remove the wires and spark plugs. Disconnect the coil-to-distributor primary wire lead at the coil and remove the coil (except integral coil HEI).
  12.  
  13. Remove the rocker arm cover. Back off the rocker arm nuts, pivot the rocker arms to clear the pushrods and remove the pushrods. Be certain to keep the pushrods in the order in which they came out. They must be returned to their original positions.
  14.  
  15. Remove the cylinder head bolts, cylinder head and gasket.
  16.  

To install:
  1. Clean the mating surfaces of the cylinder head and block. Check the cylinder head and block for warpage with a straightedge and feeler gauge. Warpage must not exceed 0.006 in. over a 6 inch span. If this limit is exceeded, the head or block should be milled flat.
  2.  
  3. Clean the head bolts and the threads in the cylinder block, since dirt will affect torque readings.
  4.  
  5. Install a new head gasket over the dowel pins. Do not use sealer on composition steel/asbestos gaskets.
  6.  
  7. Guide the cylinder head into place over the dowels and gasket.
  8.  
  9. Oil the cylinder head bolts, install and run them down snug.
  10.  
  11. Tighten the cylinder head bolts a little at a time with a torque wrench in the correct sequence. Final torque should be 90-95 ft. lbs., except for the left front head bolt, which should be tightened to 85 ft. lbs.
  12.  
  13. Install the pushrods down through the cylinder head openings and seat them in their lifter sockets.
  14.  
  15. Install the rocker arms, balls and nuts, then tighten the rocker arm nuts until all pushrod play is taken up.
  16.  
  17. Install the thermostat, thermostat housing and water outlet using new gaskets. Then connect the radiator hose.
  18.  
  19. Install the heat sending switch and tighten to 15-20 ft. lbs.
  20.  
  21. Clean the spark plugs or install new ones.
  22.  
  23. Install the coil, then connect the heat sending unit and the coil primary wires. Connect the negative battery cable at the cylinder head.
  24.  
  25. Clean the surfaces of the manifold(s) and install a new gasket or gaskets over the manifold studs. Install the manifold(s). Clean and oil the bolts, then install and tighten them in sequence to the specified values. Connect the exhaust pipe to the manifold, using a new ring gasket.
  26.  
  27. Install the carburetor (if it was removed) and reconnect the carburetor linkage.
  28.  
  29. Connect the PCV, fuel and vacuum lines, then secure the lines in the clip at water outlet.
  30.  
  31. Fill the cooling system and check for leaks.
  32.  
  33. Adjust the valve lash.
  34.  
  35. Install the rocker arm cover and position the wiring harness in the clips.
  36.  
  37. Clean and install the air cleaner.
  38.  

265, 301, 305, 326, 350, 400, 403 and 455 Engines

1967-74 MODELS

See Figure 2

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Fig. Fig. 2: It is vital to tighten the cylinder head bolts in the sequence shown to ensure proper cylinder bore sealing 1967-74 8-cylinder engines

Drain the cooling system including the block.


CAUTION
When draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

  1. Remove the intake manifold, the valley cover, and the valve covers.
  2.  
  3. Loosen the rocker arm retaining nuts and pivot the rockers off the pushrods.
  4.  
  5. Remove the pushrods and tag them as to location so that they may be returned to their same positions.
  6.  


CAUTION
Please refer to Repair Guide before discharging the compressor or disconnecting air conditioning lines. Damage to the air conditioning system or personal injury could result. Consult your local laws concerning refrigerant discharge and recycling. In many areas it may be illegal for anyone but a certified technician to service the A/C system. Always use an approved recovery station when discharging the air conditioning.

  1. On 1967-70 air conditioned models, remove the compressor hold-down bolts and move the compressor aside without disconnecting the hoses. The right motor mount-to-frame bolt must be removed and the engine jacked up about 2 in. to gain access to the right rear rocker arm cover bolt and cylinder head bolt.
  2.  
  3. Remove the exhaust pipe flange bolts, except when removing the left head on SD455 engines. On this model, it is necessary to remove the exhaust manifold retaining nuts and lower the manifold. Remove the inner side of the carburetor heat stove from the two center cylinder head bolts.
  4.  
  5. Remove the negative battery strap and the engine ground strap from the left head. Remove the engine ground strap and the automatic transmission oil filler tube bracket from the right head.
  6.  
  7. Remove the bolts and lift off the head with the exhaust manifold attached. Be careful not to damage the cylinder head surface when maneuvering it out around the power steering and brake equipment.
  8.  

To install:
  1. Check head surface for straightness, then place a new head gasket on the block.
  2.  

On 1968-70 air conditioned models, install the right rear head bolt into the head before placing the head on the block. Bolts are of three different lengths on V8s. When the bolts are properly installed, they will project an equal distance from the head.

  1. Place the cylinder head on the engine block, then install all bolts and tighten evenly to the specified torque. Tighten the bolts in 3 stages.
  2.  
  3. Install the pushrods in their original positions.
  4.  
  5. Position the rocker arms over the pushrods and tighten the ball retaining nuts to 20 ft. lbs.
  6.  
  7. Replace the rocker arm cover.
  8.  
  9. Replace the valley cover.
  10.  
  11. Replace the ground straps, oil filler tube bracket, intake manifold, and right motor mount bolts (on A/C models.)
  12.  
  13. Install the exhaust pipe flange nuts. On the 455 S.D. engine, install the left head exhaust manifold, with a new gasket.
  14.  

Most left and right cylinder heads are interchangeable. Large and small-valve heads should not be used on the same engine.

V8 1975-81 MODELS

See Figures 3 through 15

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Fig. Fig. 3: Tighten the cylinder head bolts for all 305 and 1978-79 350 (Chevrolet) engines in the sequence shown



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Fig. Fig. 4: Exploded view of the cylinder head and related components used on 305 and 1978-79 350 engines



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Fig. Fig. 5: Make certain to tighten the head bolts in the sequence shown, otherwise sealing may not be adequate 265, 301 and 400 engines



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Fig. Fig. 6: Exploded view of the cylinder head used on 265 and 301 engines



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Fig. Fig. 7: Tighten the cylinder head bolts on 403 and 1977 350 (Oldsmobile) engines in the sequence shown



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Fig. Fig. 8: After removing the intake manifold and rocker arm covers, loosen the rocker arm nuts ...



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Fig. Fig. 9: ... then remove the rocker arms, nuts and pivot balls



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Fig. Fig. 10: Either individually tag and remove the pushrods from the head ...



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Fig. Fig. 11: ... or remove the pushrods and place them in a makeshift cardboard organizer



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Fig. Fig. 12: Remove the exhaust manifolds, then the cylinder head bolts and lift the head off of the engine block



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Fig. Fig. 13: Remove the old gasket from the engine block ...



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Fig. Fig. 14: ... place rags or towels in the piston bores, then clean any residual gasket material off of the engine



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Fig. Fig. 15: Tighten the head bolts with a torque wrench use smooth even strokes


CAUTION
When draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

  1. Drain the coolant. Remove the air cleaner.
  2.  


CAUTION
Please refer to Repair Guide before discharging the compressor or disconnecting air conditioning lines. Damage to the air conditioning system or personal injury could result. Consult your local laws concerning refrigerant discharge and recycling. In many areas it may be illegal for anyone but a certified technician to service the A/C system. Always use an approved recovery station when discharging the air conditioning.

  1. Disconnect:
    1. Battery.
    2.  
    3. Radiator and heater hose from manifold.
    4.  
    5. Throttle linkage
    6.  
    7. Fuel line
    8.  
    9. Coil wires
    10.  
    11. Temperature sending unit
    12.  
    13. Power brake hose, distributor vacuum hose, and crankcase vent hoses.
    14.  

  2.  
  3. Remove:
    1. Distributor, marking position
    2.  
    3. Alternator upper bracket
    4.  
    5. Coil and bracket (where so equipped)
    6.  

  4.  
  5. On 1977 and later engines, remove all of the following with which the engine is equipped:
    1. Air cleaner bracket
    2.  
    3. Air pump and bracket
    4.  
    5. Accelerator return spring and bracket
    6.  
    7. Accelerator bellcrank
    8.  

  6.  
  7. Remove all manifold attaching bolts, and remove the intake manifold.
  8.  
  9. Disconnect the air manifold and tubes, and spark plug wires, remove the air cleaner preheater and spark plug heat shields, loosen and remove the exhaust manifold flange nuts, then lower the exhaust pipe assembly and hang it from the frame with wire.
  10.  
  11. Remove the manifold end bolts, then the center ones and remove the manifold from the engine.
  12.  
  13. Remove the rocker cover(s). Loosen the rocker nuts and pivot the rockers 90ordm; to permit removal of the pushrods. Remove the pushrods, marking the location of each.
  14.  
  15. Remove the cylinder head bolts, cylinder head, and gasket.
  16.  

To install:
  1. Inspect the gasket surfaces on the head(s). All surfaces must be clean and free of nicks and burrs. The threads on bolts and inside the bolt holes in the block must be clean. Inspect the head for warpage as described in the engine rebuilding section later in this section.
  2.  
  3. On the 301 engine, coat all rocker stud lower threads and cylinder head bolts with RTV silicone sealer. On all other engines, coat only the head bolts.
  4.  
  5. Install, reversing the removal procedures, keeping the following important points in mind:
    1. Tighten the head bolts in several stages, going in the pattern specified in the illustration.
    2.  
    3. Coat new gaskets (both sides) and headbolts with sealer, unless a composition steel-asbestos gasket is used; in that case, leave the gasket dry.
    4.  
    5. Make sure to relocate pushrods according to their markings. Adjust the valves according to the procedure labeled "Engine Not Running" before running the engine. Then, readjust the valves with the engine hot and running.
    6.  
    7. Coat new rocker cover gaskets with sealer, and tighten cover bolts to specified torque evenly in several stages.
    8.  

  6.  

231 Engine See Figure 16

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Fig. Fig. 16: Make sure to follow the sequence shown when tightening the cylinder head bolts on 231 V6 engines

On vehicles equipped with AIR, disconnect the rubber hose at the injection tubing check valve. This way the tubing will not have to be removed from the exhaust manifold.


CAUTION
When draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

  1. Remove the intake manifold as detailed later in this section.
  2.  
  3. When removing the right cylinder head:
    1. Loosen and remove all drive belts.
    2.  
    3. Tag and disconnect the wires leading from the rear of the alternator.
    4.  

  4.  


CAUTION
Please refer to Repair Guide before discharging the compressor or disconnecting air conditioning lines. Damage to the air conditioning system or personal injury could result. Consult your local laws concerning refrigerant discharge and recycling. In many areas it may be illegal for anyone but a certified technician to service the A/C system. Always use an approved recovery station when discharging the air conditioning.

  1. Remove the air conditioning compressor (if so equipped) and position it out of the way with all the hoses still connected.
  2.  
  3. Remove the alternator and its mounting bracket.
  4.  

  1. When removing the left cylinder head:
    1. Remove the oil dipstock and tube.
    2.  
    3. Remove the power steering pump (if so equipped) and its bracket, then position it out of the way with the hoses still attached.
    4.  

  2.  
  3. Tag and disconnect the spark plug wires, then remove the spark plug wire clips from the cylinder head cover studs.
  4.  
  5. Remove the exhaust manifold mounting bolts from the head, which is being removed, then pull the manifold away from the head.
  6.  
  7. Use an air hose, if available, or a bunch of clean rags and clean the dirt off the head and surrounding areas thoroughly. It is extremely important to avoid getting dirt into the hydraulic valve lifters.
  8.  
  9. Remove the cylinder head cover from the top of the head that you wish to remove.
  10.  
  11. Remove the rocker arm and shaft assembly from the cylinder head, then remove the pushrods.
  12.  

If the valve lifters are to be serviced, remove them at this time. Otherwise, protect the lifters and the camshaft from dust and dirt by covering the entire area with a clean cloth. Whenever the lifters or the pushrods are removed from the head it is always a good idea to place them in a wooden block with numbered holes to keep them identified as to their position in the engine.

  1. Loosen and remove all the cylinder head bolts and lift off the head.
  2.  

To install:
  1. Clean the engine block gasket surface thoroughly. Make sure that no foreign material has fallen into the cylinder bores, the bolt holes or into the valve lifter area. It is always a good idea to clean out the bolt holes with an air hose, if one is available.
  2.  
  3. Install a new head gasket with the head facing down toward the cylinder block. The dowels in the block will hold the gasket in place.
  4.  
  5. Clean the gasket surface of the cylinder head and carefully set it into place on the dowels in the cylinder block.
  6.  
  7. Use a heavy body thread sealer on all of the head bolts, since the bolt holes go all the way through into the coolant.
  8.  
  9. Install the head bolts. Tighten the bolts a little at a time (about three times around) in the sequence shown in the illustration. Tighten the bolts to a final torque equal to that given in the Torque Specifications chart.
  10.  
  11. Installation of the remaining components is in the reverse order of removal.
  12.  

VALVE GUIDES



Pontiac engines have integral valve guides. Pontiac offers valves with oversize stems for worn guides (0.001, 0.003 and 0.005 in. being available for most engines). To fit these, enlarge the valve guide bores with valve guide reamers to an oversize that cleans up the wear. If a large oversize is required, it is best to approach that size in stages by using a series of reamers of increasing diameter. This helps to maintain the concentricity of the guide bores with the valve seats. The correct valve stem-to-guide clearance is given in the Valve Specifications table at the beginning of this section. As an alternate procedure, some automotive machine shops can fit replacement guides that use standard stem valves or knurl the guides if wear permits. Valve guide procedures are provided at the end of this section.

VALVE ADJUSTER & ROCKER ARM SERVICE OHC 230 and 250 Engines



See Figure 17

Click image to see an enlarged view

Fig. Fig. 17: Exploded view of the valve lash adjuster used by the OHC 230 and 250 engines

This engine is equipped with hydraulic valve lash adjusters. These adjusters are located in the cylinder head and serve as a fulcrum for the rocker arms, and locate the rocker arms accurately with the camshaft lobes. This lash adjuster is similar to the lifter used in a conventional pushrod engine. However, the lash adjuster remains stationary to maintain adjustment at all times. The rocker arm is attached to the adjuster with a spring clip. These adjusters are serviced in the same manner as conventional hydraulic tappets.

  1. Remove the rocker cover assembly.
  2.  
  3. Remove the rocker arm and hydraulic lash adjuster assemblies, keeping them in proper order for correct installation in their original positions.
  4.  
  5. If the lash adjuster sticks in its bore, proceed as follows:
    1. Remove the rocker arm.
    2.  
    3. Fill the vent hole adjacent to the lifter with SAE 30 oil.
    4.  
    5. Insert a 4 in. length of 3 / 16 in. diameter rod into the vent hole and strike the end of the rod sharply with a hammer.
    6.  

  6.  

The hydraulic pressure generated in this operation should be sufficient to dislodge even the most stubborn adjuster.

  1. To install, reverse the removal procedure, with the exception of Step 3.
  2.  

HYDRAULIC VALVE LIFTER DISASSEMBLY 1970-81 Models



See Figure 18

Click image to see an enlarged view

Fig. Fig. 18: Exploded view of a typical hydraulic valve lifter

Lifters are disassembled for cleaning only. Lifters should slide easily from their bores. If not, use a magnet to raise the lifter in its bore, then grasp and remove it with a pair of pliers. Be careful not to gouge the lifter jacket.

  1. Grasp the lockring with needlenose pliers and remove it. (Depress the plunger to gain clearance).
  2.  
  3. Remove the pushrod cup, metering valve disc, and upper metering disc (if any). Do not bend the metering disc.
  4.  
  5. Remove the plunger assembly and plunger spring.
  6.  
  7. Remove the spring, check valve retainer, and check valve from the plunger.
  8.  
  9. Clean all parts in solvent (lacquer thinner is good) and reassemble.
  10.  

Internal parts should not be interchanged between lifters.

 
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