REMOVAL & INSTALLATION
151 Four and 250 Inline Six Cylinder Engines
1975 and 1976 250 6-cylinder engines are equipped with an intake manifold which is integrally cast with the cylinder head and cannot be removed. The 1974 250 6-cylinder uses a combined intake and exhaust manifold; both are removed together. Likewise, the 1977 and 1978 151 4-cylinder intake and exhaust manifolds are combined and are removed together. The 1979 151 manifolds are bolted to opposite sides of the head; 1979 4-cylinder exhaust manifold removal and installation is covered under "Exhaust Manifold."
- Remove the air cleaner assembly and air ducts.
- On 1979 151 fours, drain the cooling system.
- Tag and disconnect the throttle linkage at the carburetor. Tag and disconnect the fuel line, vacuum lines, hoses, and electrical connections.
- Disconnect the transmission downshift linkage (if equipped), and remove the PCV valve from the rocker cover. On models equipped with air injection, disconnect the air supply hose from the check valve on the air injection manifold.
- Remove the carburetor, with spacer and heat shield (if equipped).
- Spray the nuts and bolts connecting the exhaust manifold to the exhaust pipe with a rust penetrant, as these are usually quite difficult to remove. Unbolt the exhaust manifold from the pipe.
It may be necessary to remove the generator rear bracket and/or A/C bracket on some models.
- Unbolt the manifold bolts and clamps, and remove the manifold assembly. On 1979 151 fours, remove the intake manifold.
- If you intend to separate the manifolds, remove the single bolt and two nuts at the center of the 250 six manifold assembly. On 1977 and 1978 151 fours, disconnect the EGR pipe and remove the four bolts at the center of the manifold.
- Installation is the reverse of removal. When assembling the manifolds, install the connecting bolts loosely first. Place the manifolds on a straight, flat surface and hold them securely during tightening-this assures the proper mating of surfaces when the manifold assembly is fastened to the head. Stress cracking could occur if the manifolds are not assembled first in this manner. On the 1977 and '78 151 four, be sure the insulator gasket is in place between the early fuel evaporation (EFE) bracket and the manifold. On all manifolds, always use new gaskets between the manifolds and cylinder head. Tighten the manifold bolts in the patterns illustrated.
- Drain the cooling system.
- Remove the air cleaner assembly.
- Remove the thermostat housing and the bypass hose. It is not necessary to remove the top radiator hose from the thermostat housing.
- Disconnect the heater hose at the rear of the manifold.
- Disconnect all electrical connections and vacuum lines from the manifold. Remove the EGR valve if necessary.
- On vehicles equipped with power brakes remove the vacuum line from the vacuum booster to the manifold.
- Remove the distributor (if necessary).
- Remove the fuel line to the carburetor.
- Remove the carburetor linkage.
- Remove the carburetor.
- Remove the intake manifold bolts. Remove the manifold and the gaskets. Remember to reinstall the O-ring seal between the intake manifold and timing chain cover during assembly, if so equipped.
- Installation is the reverse of removal. Use plastic gasket retainers to prevent the manifold gasket from slipping out of place, if so equipped.
Before installing the intake manifold, be sure that the gasket surfaces are thoroughly clean.350 DIESEL
- Remove the air cleaner.
- Drain the radiator. Loosen the upper bypass hose clamp, remove the thermostat housing bolts, and remove the housing and the thermostat from the intake manifold.
- Remove the breather pipes from the rocker covers and the air crossover. Remove the air crossover.
- Disconnect the throttle rod and the return spring. If equipped with cruise control, remove the servo.
- Remove the hairpin clip at the bellcrank and disconnect the cables. Remove the throttle cable from the bracket on the manifold; position the cable away from the engine. Disconnect and label any wiring as necessary.
- Remove the alternator bracket if necessary. If equipped with air conditioning, remove the compressor mounting bolts and move the compressor aside, without disconnecting any of the hoses. Remove the compressor mounting bracket from the intake manifold.
- Disconnect the fuel line from the pump and the fuel filter. Remove the fuel filter and bracket.
- Remove the fuel injection pump and lines. See , "Fuel System," for procedures.
- Disconnect and remove the vacuum pump or oil pump drive assembly from the rear of the engine.
- Remove the intake manifold drain tube.
- Remove the intake manifold bolts and remove the manifold. Remove the adapter seal. Remove the injection pump adapter.
- Clean the mating surfaces of the cylinder heads and the intake manifold using a putty knife.
- Coat both sides of the gasket surface that seal the intake manifold to the cylinder heads with G.M. sealer #1050026 or the equivalent. Position the intake manifold gaskets on the cylinder heads. Install the end seals, making sure that the ends are positioned under the cylinder heads.
- Carefully lower the intake manifold into place on the engine.
- Clean the intake manifold bolts thoroughly, then dip them in clean engine oil. Install the bolts and tighten to 15 ft. lbs. in the sequence shown. Next, tighten all the bolts to 30 ft. lbs., in sequence, and finally tighten to 40 ft. lbs. in sequence.
- Install the intake manifold drain tube and clamp.
- Install injection pump adapter. See . If a new adapter is not being used, skip steps 4 and 9.