GM Astro/Safari 1985-1996 Repair Guide

Cylinder Head

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REMOVAL & INSTALLATION



2.5L Engine

See Figures 1 and 2



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Fig. Fig. 1: Exploded view of the cylinder head mounting-2.5L engine



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Fig. Fig. 2: Cylinder head bolt torque sequence-2.5L engine

Before disassembling the engine, make sure that it is overnight cold.


CAUTION
Relieve the pressure on the fuel system before disconnecting any fuel line connection!

  1. From inside the vehicle, remove the engine cover. For details, please refer to General Information & Maintenance of this information.
  2.  
  3. Properly relieve the fuel system pressure, then disconnect the negative battery cable for safety.
  4.  
  5. Place a catch pan under the radiator, open the drain cock and drain the cooling system.
  6.  


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

  1. Remove the rocker arm cover. For details, please refer to the procedure found earlier in this section.
  2.  
  3. Disconnect the accelerator, cruise control and the TVS cables, as equipped.
  4.  
  5. From the intake manifold, remove the water pump bypass and heater hoses.
  6.  
  7. From the alternator, remove the front and rear braces, then move it aside.
  8.  
  9. Disconnect the air conditioning compressor brackets, then reposition and support the compressor aside. Be sure not to stress or damage the A/C refrigerant lines.
  10.  
  11. Remove the thermostat housing-to-cylinder head bolts and the housing from the engine.
  12.  
  13. Remove the ground cable and any necessary electrical connectors from the cylinder head. TAG and disconnect the ignition wires from the spark plugs and disengage the oxygen sensor lead. Disconnect and remove the ignition coil from the intake manifold and the cylinder head.
  14.  
  15. Tag and remove the vacuum lines and fuel hoses from the intake manifold and the TBI unit.
  16.  
  17. Disconnect the exhaust pipe from the exhaust manifold.
  18.  
  19. Remove the rocker arm nuts, the washers, the rocker arms and the pushrods from the cylinder head.
  20.  

If the rocker arm and pushrod assemblies are not being replaced BE SURE TO TAG or ARRANGE them. If they are reused, they MUST be installed in their original locations.

  1. Remove the cylinder head-to-engine bolts, then remove the cylinder head from the engine (with the manifolds attached).
  2.  
  3. Place the assembly on a workbench. If necessary, remove the intake and the exhaust manifolds from the cylinder head.
  4.  
  5. Using a plastic scraper, clean the gasket mounting surfaces. Using a wire brush, clean the carbon deposits from the combustion chambers.
  6.  
  7. Inspect the cylinder head and block for cracks, nicks, heavy scratches or other damage.
  8.  

To install:
  1. If removed, install the intake and/or exhaust manifolds to the cylinder head using new gaskets.
  2.  
  3. Use new gaskets, sealant (where necessary, refer to the illustration and any instructions which came with the gasket kit) and install the cylinder head onto the block.
  4.  
  5. Tighten all of the cylinder head bolts (in sequence) to 18 ft. lbs. (25 Nm). Then tighten all bolts (except #9) to 26 ft. lbs. (35 Nm). Retighten the #9 bolt to 18 ft. lbs. (25 Nm). Then tighten all bolts an additional 90 degrees ( 1 / 4 turn) in sequence.
  6.  
  7. Loosely install the pushrods, rocker arms and nuts. Adjust the valve lash and secure the rocker arm assemblies as detailed in General Information & Maintenance of this information or earlier in this section under Rocker Arm removal and installation.
  8.  
  9. Connect the exhaust pipe to the exhaust manifold.
  10.  
  11. Install the vacuum lines and fuel hoses to the intake manifold and the TBI unit as tagged during removal.
  12.  
  13. Install the ground cable and any necessary electrical connectors from the cylinder head. Connect the ignition wires to the spark plugs (as tagged during removal) and engage the oxygen sensor lead. Connect the ignition coil to the intake manifold and the cylinder head.
  14.  
  15. Install the thermostat housing and housing-to-cylinder head bolts to the engine.
  16.  
  17. Connect the air conditioning compressor brackets.
  18.  
  19. To the alternator, install the front and rear braces.
  20.  
  21. To the intake manifold, install the water pump bypass and heater hoses.
  22.  
  23. Connect the accelerator, cruise control and TVS cables, as equipped.
  24.  
  25. Install the rocker arm cover.
  26.  
  27. Connect the negative battery cable.
  28.  
  29. Properly refill and bleed the engine cooling system, then check for leaks.
  30.  
  31. Once the engine has cooled sufficiently, install the engine cover to the passenger compartment.
  32.  

4.3L Engine

See Figures 3, 4, 5, 6, 7, 8, 9, 10 and 11



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Fig. Fig. 3: Prepare the cylinder head by removing the rocker arm cover, intake manifold, and exhaust manifold



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Fig. Fig. 4: Loosen the cylinder head bolts using the reverse of the torque sequence ...



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Fig. Fig. 5: ... a breaker bar, socket and various length extensions are necessary to remove the bolts



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Fig. Fig. 6: Once all the bolts are removed, break the gasket seal and lift the cylinder head from the block



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Fig. Fig. 7: Protect the lifter valley and pistons bores using rags or a plastic cover ...



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Fig. Fig. 8: ... then carefully clean the gasket mating surfaces of all old gasket and debris



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Fig. Fig. 9: Upon installation, tighten the cylinder head bolts using the proper torque sequence



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Fig. Fig. 10: Exploded view of a typical 4.3L engine cylinder head-1996 shown



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Fig. Fig. 11: Cylinder head torque sequence-4.3L engines

1985-90 Models

CAUTION
If equipped with a TBI system, relieve the pressure on the fuel system before disconnecting any fuel line connection.

  1. From inside the vehicle, remove the engine cover. For details, please refer to General Information & Maintenance of this information.
  2.  
  3. Properly relieve the fuel system pressure, then disconnect the negative battery cable for safety.
  4.  
  5. Place a catch pan under the radiator, open the drain cock and drain the cooling system.
  6.  


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

  1. Remove the rocker arm cover.
  2.  
  3. Remove the intake manifold.
  4.  
  5. Remove the exhaust manifold.
  6.  
  7. Remove the AIR pipe at the rear of the head.
  8.  
  9. If removing the right cylinder head, remove or disconnect:

    AIR pump mounting bolt and spacer at the head.
     
    Engine accessory bracket bolts and studs at the head.
     
    Wiring harness and clip at the rear of the head.
     

  10.  
  11. If removing the left cylinder head, remove or disconnect:

    Engine accessory bracket bolts and studs at the head. It may be necessary to loosen the remaining bracket bolts to provide clearance for head removal.
     
    Fuel pipes and bracket at the rear of the head.
     
    Coolant sensor wire.
     
    Cruise control transducer bracket, if equipped.
     

  12.  
  13. Tag and disconnect the wiring from the spark plugs. If necessary, remove the spark plugs from the cylinder head.
  14.  
  15. Loosen the rocker arms and remove the pushrods.
  16.  

If valve train components, such as the rocker arms or pushrods, are to be reused, they must be tagged or arranged to insure installation in their original locations.

  1. Remove the cylinder head bolts by loosening them in the reverse of the torque sequence, then carefully remove the cylinder head.
  2.  
  3. Using a plastic scraper, clean the gasket mounting surfaces.
  4.  
  5. Clean the carbon deposits from the combustion chambers.
  6.  
  7. Inspect the cylinder head and block for cracks, nicks, heavy scratches or other damage.
  8.  

To install:

The gasket surfaces on both the head and block must be clean of any foreign matter and free of nicks or heavy scratches. The cylinder bolt threads in the block and threads on the bolts must be cleaned (dirt will affect the bolt torque).

DO NOT apply sealer to composition steel-asbestos gaskets.

  1. If using a steel only gasket, apply a thin and even coat of sealer to both sides of the gaskets.
  2.  
  3. Place a new gasket over the dowel pins with the bead or the words "This Side Up'' facing upwards (as applicable), then carefully lower the cylinder head into position over the gasket and dowels.
  4.  
  5. Apply a coating of GM 1052080 or an equivalent sealer to the threads of the cylinder head bolts, then thread the bolts into position until finger-tight. Using the proper torque sequence, tighten the bolts in 3 steps:

    First, tighten the bolts to 25 ft. lbs. (34 Nm).
     
    Next, tighten the bolts to 45 ft. lbs. (61 Nm).
     
    Finally, tighten the bolts to 65 ft. lbs. (90 Nm).
     

  6.  
  7. Install the pushrods, secure the rocker arms and adjust the valves.
  8.  
  9. If removed, install the spark plugs. Engage the spark plug wires and make sure they are positioned in the wire brackets.
  10.  
  11. If the left cylinder head was removed, reposition and secure the engine accessory bracket bolts and studs, the fuel pipes and bracket at the rear of the head, the coolant sensor wire and, if equipped, the cruise control transducer bracket.
  12.  
  13. If the right cylinder head was removed, install the AIR pump mounting bolt and spacer at the head, the engine accessory bracket bolts and studs and the wiring harness and clip at the rear of the head.
  14.  
  15. Connect the AIR pipe at the rear of the head.
  16.  
  17. Install the exhaust manifold.
  18.  
  19. Install the intake manifold.
  20.  
  21. Install the rocker arm cover.
  22.  
  23. Connect the negative battery cable, then properly refill the engine cooling system.
  24.  
  25. Run the engine to check for leaks, then check and/or adjust the ignition timing.
  26.  
  27. Once the engine has cooled sufficiently, install the engine cover to the passenger compartment.
  28.  

1991-95 Models

CAUTION
Relieve the pressure on the fuel system before disconnecting any fuel line connection.

  1. From inside the vehicle, remove the engine cover. For details, please refer to General Information & Maintenance of this information.
  2.  
  3. Properly relieve the fuel system pressure, then disconnect the negative battery cable for safety.
  4.  
  5. Place a catch pan under the radiator, open the drain cock and drain the cooling system.
  6.  


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

  1. Remove the rocker arm cover.
  2.  
  3. Remove the intake manifold.
  4.  
  5. Remove the exhaust manifold.
  6.  
  7. Remove the engine accessory bracket bolts and studs at the head.
  8.  
  9. Disconnect the wiring harness clip at the rear of the head.
  10.  
  11. Remove the fuel pipes and bracket from the rear of the head.
  12.  
  13. Disconnect the coolant sensor wire.
  14.  
  15. If equipped, remove the cruise control transducer bracket.
  16.  
  17. Tag and disconnect the wiring from the spark plugs. If necessary, remove the spark plugs from the cylinder head.
  18.  
  19. Loosen the rocker arms and remove the pushrods.
  20.  

If valve train components, such as the rocker arms or pushrods, are to be reused, they must be tagged or arranged to insure installation in their original locations.

  1. Remove the cylinder head bolts by loosening them in the reverse of the torque sequence, then carefully remove the cylinder head.
  2.  
  3. Using a plastic scraper, clean the gasket mounting surfaces.
  4.  
  5. Clean the carbon deposits from the combustion chambers.
  6.  
  7. Inspect the cylinder head and block for cracks, nicks, heavy scratches or other damage.
  8.  

To install:

The gasket surfaces on both the head and block must be clean of any foreign matter and free of nicks or heavy scratches. The cylinder bolt threads in the block and threads on the bolts must be cleaned (dirt will affect the bolt torque).

DO NOT apply sealer to composition steel-asbestos gaskets.

  1. If using a steel only gasket, apply a thin and even coat of sealer to both sides of the gaskets.
  2.  
  3. Place a new gasket over the dowel pins with the bead or the words "This Side Up'' facing upwards (as applicable), then carefully lower the cylinder head into position over the gasket and dowels.
  4.  
  5. Apply a coating of GM 1052080 or an equivalent sealer to the threads of the cylinder head bolts, then thread the bolts into position until finger-tight. Using the proper torque sequence, tighten the bolts in 3 steps:

    First, tighten the bolts to 25 ft. lbs. (34 Nm).
     
    Next, tighten the bolts to 45 ft. lbs. (61 Nm).
     
    Finally, tighten the bolts to 65 ft. lbs. (90 Nm).
     

  6.  
  7. Install the pushrods, secure the rocker arms and adjust the valves.
  8.  
  9. If removed, install the spark plugs. Engage the spark plug wires and make sure they are positioned in the wire brackets.
  10.  
  11. Install the engine accessory bracket bolts and studs at the head.
  12.  
  13. Secure the wiring harness and clip at the rear of the head.
  14.  
  15. Install the fuel pipes and bracket at the rear of the head.
  16.  
  17. Engage the coolant sensor wiring connector.
  18.  
  19. If equipped, install the cruise control transducer bracket.
  20.  
  21. Install the exhaust manifold.
  22.  
  23. Install the intake manifold.
  24.  
  25. Install the rocker arm cover.
  26.  
  27. Connect the negative battery cable, then properly refill the engine cooling system.
  28.  
  29. Run the engine to check for leaks, then check and/or adjust the ignition timing.
  30.  
  31. Once the engine has cooled sufficiently, install the engine cover to the passenger compartment.
  32.  

1996 Models

CAUTION
Relieve the pressure on the fuel system before disconnecting any fuel line connection.

  1. From inside the vehicle, remove the engine cover. For details, please refer to General Information & Maintenance of this information.
  2.  
  3. Properly relieve the fuel system pressure, then disconnect the negative battery cable for safety.
  4.  
  5. Place a catch pan under the radiator, open the drain cock and drain the cooling system.
  6.  


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

  1. Remove the rocker arm cover.
  2.  
  3. Remove the intake manifold.
  4.  
  5. Remove the exhaust manifold.
  6.  
  7. Remove the alternator and bracket.
  8.  
  9. Disconnect the wiring harness clip at the rear of the head.
  10.  
  11. Disconnect the coolant sensor wire.
  12.  
  13. Tag and disconnect the wiring from the spark plugs. If necessary, remove the spark plugs from the cylinder head.
  14.  
  15. Loosen the rocker arms and remove the pushrods.
  16.  

If valve train components, such as the rocker arms or pushrods, are to be reused, they must be tagged or arranged to insure installation in their original locations.

  1. Remove the cylinder head bolts by loosening them in the reverse of the torque sequence, then carefully remove the cylinder head.
  2.  
  3. Using a plastic scraper, clean the gasket mounting surfaces.
  4.  
  5. Clean the carbon deposits from the combustion chambers.
  6.  
  7. Inspect the cylinder head and block for cracks, nicks, heavy scratches or other damage.
  8.  

To install:

The gasket surfaces on both the head and block must be clean of any foreign matter and free of nicks or heavy scratches. The cylinder bolt threads in the block and threads on the bolts must be cleaned (dirt will affect the bolt torque).

DO NOT apply sealer to composition steel-asbestos gaskets.

  1. If using a steel only gasket, apply a thin and even coat of sealer to both sides of the gaskets.
  2.  
  3. Place a new gasket over the dowel pins with the bead or the words "This Side Up'' facing upwards (as applicable), then carefully lower the cylinder head into position over the gasket and dowels.
  4.  
  5. Apply a coating of GM 1052080 or an equivalent sealer to the threads of the cylinder head bolts, then thread the bolts into position until finger-tight. Using the proper torque sequence, tighten the bolts to 22 ft. lbs. (30 Nm), then using a torque angle meter, tighten the bolts the additional specified amount based on bolt size and position in the torque sequence.

    Short length bolts (11, 7, 3, 2, 6 and 10) should be tightened an additional 55 degrees.
     
    Medium length bolts (12, and 13) should be tightened an additional 65 degrees.
     
    Long length bolts (1, 4, 8, 5, and 9) should be tightened an additional 75 degrees.
     

  6.  
  7. Install the pushrods and rocker arms.
  8.  
  9. If removed, install the spark plugs. Engage the spark plug wires and make sure they are positioned in the wire brackets.
  10.  
  11. Install the alternator and bracket.
  12.  
  13. Secure the wiring harness and clip at the rear of the head.
  14.  
  15. Engage the coolant sensor wiring connector.
  16.  
  17. Install the exhaust manifold.
  18.  
  19. Install the intake manifold.
  20.  
  21. Install the rocker arm cover.
  22.  
  23. Connect the negative battery cable, then properly refill the engine cooling system.
  24.  
  25. Run the engine to check for leaks, then check and/or adjust the ignition timing.
  26.  
  27. Once the engine has cooled sufficiently, install the engine cover to the passenger compartment.
  28.  

CLEANING AND INSPECTION



See Figures 12, 13, 14 and 15



Click image to see an enlarged view

Fig. Fig. 12: Use a gasket scraper to remove the bulk of the old head gasket material from the mating surface ...



Click image to see an enlarged view

Fig. Fig. 13: ... but an electric drill equipped with a wire wheel will expedite complete gasket removal



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Fig. Fig. 14: Clean the combustion chambers using a wire brush-if the valves are removed use care around the valve seats



Click image to see an enlarged view

Fig. Fig. 15: If the cylinder head is disassembled, use an expandable wire type tool to clean the valve guides

  1. With the valves installed to protect the valve seats, remove carbon deposits from the combustion chambers and valve heads using a drill-mounted wire brush. Be careful not to damage the cylinder head gasket surface. If the head is to be disassembled, proceed to Step 3. If the head is not to be disassembled, proceed to Step 2.
  2.  
  3. Remove all dirt, oil and old gasket material from the cylinder head with solvent. Clean the bolt holes and the oil passage. Be careful not to get solvent on the valve seals as the solvent may damage them. If available, dry the cylinder head with compressed air. Check the head for cracks or other damage, and check the gasket surface for burrs, nicks and flatness. If you are in doubt about the head's serviceability, consult a reputable automotive machine shop.
  4.  
  5. Remove the valves, springs and retainers, then clean the valve guide bores with a valve guide cleaning tool. Remove all dirt, oil and old gasket material from the cylinder head with solvent. Clean the bolt holes and the oil passage.
  6.  

Excessive valve stem-to-bore clearance will cause excessive oil consumption and may cause valve breakage. Insufficient clearance will result in noisy and sticky functioning of the valve and disturb engine smoothness.

  1. Remove all deposits from the valves with a wire brush or buffing wheel. Inspect the valves as described later in this section.
  2.  
  3. Check the head for cracks using a dye penetrant in the valve seat area and ports, head surface and top. Check the gasket surface for burrs, nicks and flatness. If you are in doubt about the head's serviceability, consult a reputable automotive machine shop.
  4.  

If the cylinder head was removed due to an overheating condition and a crack is suspected, do not assume that the head is not cracked because a crack is not visually found. A crack can be so small that it cannot be seen by eye, but can pass coolant when the engine is at operating temperature. Consult an automotive machine shop that has pressure testing equipment to make sure the head is not cracked.

RESURFACING



See Figures 16, 17 and 18



Click image to see an enlarged view

Fig. Fig. 16: Check the cylinder head for warpage across each of these surface angles



Click image to see an enlarged view

Fig. Fig. 17: Check the cylinder head for flatness across the head surface



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Fig. Fig. 18: Checks should be made both straight across the head and a both diagonals

Whenever the cylinder head is removed, check the flatness of the cylinder head gasket surface as follows:

  1. Make sure all dirt and old gasket material has been cleaned from the cylinder head. Any foreign material left on the head gasket surface can cause a false measurement.
  2.  
  3. Place a straightedge straight across and diagonally across the gasket surface of the cylinder head (in the positions shown in the figures). Using feeler gauges, determine the clearance at the center of the straightedge.
  4.  
  5. If warpage exceeds the 0.004 in. (0.10mm) then the cylinder head should likely be resurfaced or replaced. Contact a reputable machine shop for machining service and recommendations.
  6.  

When resurfacing the cylinder head(s), the intake manifold mounting position is altered and must be corrected by machining a proportionate amount from the intake manifold flange.

CYLINDER BLOCK CLEANING



While the cylinder head is removed, the top of the cylinder block and pistons should also be cleaned. Before you begin, rotate the crankshaft until one or more pistons are flush with the top of the block. Carefully stuff clean rags into the cylinders in which the pistons are down. This will help keep grit and carbon chips out during cleaning. Using care not to gouge or scratch the block-to-head mating surface and the piston top(s), clean away any old gasket material with a wire brush and/or scraper. On the piston tops, make sure you are actually removing the carbon and not merely burnishing it.

Remove the rags from the down cylinders after you have wiped the top of the block with a solvent soaked rag. Rotate the crankshaft until the other pistons come up flush with the top of the block, and clean those pistons.

Because you have rotated the crankshaft, you may have to re-time the ignition during installation. It is probably easiest to set the engine to No. 1 TDC before installing the cylinder head. Also, make sure you wipe out each cylinder thoroughly with a solvent-soaked rag, to remove all traces of grit, before the head is reassembled to the block.

 
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