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1. CAUTION: At no time, when the timing chain(s) are removed and the cylinder heads (6049) are installed, may the crankshaft (6303) and camshafts (6250) be rotated. Failure to follow these directions will result in valve and/or piston damage. NOTE: Because this is not a free-wheeling engine, if it has jumped time, there will be damage to the valves and pistons (6108) and will require the removal of the cylinder heads . The camshaft sprockets (6256) should only be disassembled from the camshafts when one of the components is to be replaced. Remove valve covers (6582) , oil pan (6675) and engine front cover (6019) as described. 2. Remove crankshaft position sensor pulse wheel. 3. Rotate engine to No. 1 top dead center (TDC). 4. NOTE: Cam Positioning Tool Adapters 303-413 (T92P-6256-A) and Cam Positioning Tool 303-380 (T91P-6256-A) MUST be installed on camshaft to prevent camshaft from rotating. Install Cam Positioning Tool Adapters 303-413 (T92P-6256-A) and Cam Positioning Tool 303-380 (T91P-6256-A) on flats of camshafts . 5. Remove two bolts retaining RH timing chain tensioner (6L266) to cylinder head and remove timing chain tensioner . 6. Remove RH timing chain tensioner arm (6L253) . 7. Remove two bolts retaining RH timing chain guide (6K297) to cylinder head and remove timing chain guide . 8. Remove RH timing chain from camshaft sprocket and crankshaft sprockets (6306) . 9. NOTE: Cam Positioning Tool Adapters 303-413 (T92P-6256-A) and Cam Positioning Tool 303-380 (T91P-6256-A) MUST be installed on camshaft to prevent camshaft from rotating. Remove two bolts retaining LH timing chain tensioner to cylinder head and remove timing chain tensioner . 10. Remove LH timing chain tensioner arm . 11. Remove two bolts retaining LH timing chain guide to cylinder head and remove timing chain guide . 12. Remove LH timing chain from camshaft sprocket and crankshaft sprocket . 13. If necessary, remove camshaft sprockets and crankshaft sprockets as described. 14. CAUTION: Do not rotate crankshaft and/or camshafts . Engine damage may occur. Inspect the plastic running face on timing chain tensioner arms and timing chain guides . If worn or damaged, remove and clean oil pan and oil pump screen cover and tube (6622) . Installation

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1. CAUTION: At no time, when the timing chain(s) are removed and the cylinder heads (6049) are installed, may the crankshaft (6303) and/or camshafts (6250) be rotated. Failure to follow these directions will result in valve and/or piston damage. NOTE: Because this is not a free-wheeling engine, and it jumps time, there will be damage to the valves and/or pistons (6108) and will require the removal of the cylinder heads. The camshaft sprockets (6256) should only be disassembled from the camshafts when one of the components is to be replaced. Remove valve covers (6582) and engine front cover (6019) as described. 2. Remove crankshaft position sensor pulse wheel. 3. Rotate engine to No. 1 top dead center (TDC). 4. NOTE: This will prevent accidental rotation of the camshafts. NOTE: Cam Positioning Tool Adapters T92P-6256-A and Cam Positioning Tool T91P-6256-A must be installed on camshaft to prevent camshaft from rotating. Install Cam Positioning Tool Adapters T92P-6256-A and Cam Positioning Tool T91P-6256-A on flats of camshaft. 5. Remove two bolts retaining RH timing chain tensioner (6L266) to cylinder head and remove timing chain tensioner. 6. Remove RH timing chain tensioner arm (6L253). 7. Remove two bolts retaining RH timing chain guide (6K297) to cylinder head and remove timing chain guide. 8. Remove RH timing chain from camshaft sprocket and crankshaft sprocket (6306). 9. NOTE: Cam Positioning Tool Adapters T92P-6256-A and Cam Positioning Tool T91P-6256-A must be installed on camshaft to prevent camshaft from rotating. Remove two bolts retaining LH timing chain tensioner to cylinder head and remove timing chain tensioner. 10. Remove LH timing chain tensioner arm. 11. Remove two bolts retaining LH timing chain guide to cylinder head and remove timing chain guide. 12. Remove LH timing chain from camshaft sprocket and crankshaft sprocket. 13. If necessary, remove camshaft sprockets and crankshaft sprockets as described. 14. CAUTION: Do not rotate crankshaft and/or camshafts or possible engine damage may occur. Inspect the plastic running face on timing chain tensioner arms and timing chain guides. If worn or damaged, remove and clean oil pan (6675) and oil pump screen cover and tube (6622).

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Note: GM does not provide timing chain timing marks, or information to perform timing chain service without the special tools shown in this procedure. Tools Required: – - J 36800 Camshaft Sprocket Timing Alignment Pin J 39579 Camshaft Sprocket Wrench Important: ^ ^ Before remove the timing chain, read the entire procedure. The timing chain on the engine is not to be replaced with the timing chain from any other model year. The timing sprockets are different on the engine and the shape of the links matches the sprockets. Engine damage may result if the wrong timing chain is used. The timing chain and the crankshaft sprocket must be marked in order to insure reassembly with the same side facing out at the time of reassembly. ^ Caution: Refer to Battery Disconnect Caution in Service Precautions. 1. Disconnect the negative battery cable. 2. Remove the engine front cover. Refer to Engine Front Cover Replacement. 3. Rotate the crankshaft clockwise (as viewed from the front of the engine, normal rotation) until the camshaft sprocket timing dowel pin holes line up with the holes in the timing chain housing. 4. The crankshaft sprocket keyway should point upwards and line up with the centerline of the cylinder bores. This is the Timed position. 5. Remove the timing chain guides. 6. Raise and support the vehicle. Refer to Vehicle Lifting. 7. Ensure that all of the slack in the timing chain is above the tensioner assembly. 8. Remove the timing chain tensioner. 9. The timing chain must be disengaged from any wear grooves in the tensioner shoe in order to remove the shoe. Slide a screwdriver blade under the timing chain while pulling the shoe outward. Notice: Do NOT attempt to pry the sprocket off the camshaft or damage to the sprocket or chain housing could occur. 10. If difficulty is encountered in removing the timing chain tensioner shoe, use the following procedure in order to remove the intake camshaft sprocket: 10.1. 10.2. 10.3. 10.4. Lower the vehicle. Hold the intake camshaft sprocket with the J 39579 and remove the sprocket bolt and washer. Remove the washer from the bolt and rethread the bolt back into the camshaft by hand (the bolt provides a surface to push against). Remove the intake camshaft sprocket. Use a three-jaw puller in the three relief holes in the sprocket.

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4. Align crankshaft sprocket timing mark to the mark on oil pump housing (Fig. 122). NOTE: Lubricate timing chain and guides with engine oil before installation. 5. Place left side primary chain sprocket onto the chain so that the timing mark is located in-between the two (plated) timing links (Fig. 122). 6. Lower the primary chain with left side sprocket through the left cylinder head opening. NOTE: The camshaft sprockets can be allowed to float on the camshaft hub during installation 1 – CAMSHAFT TIMING MARKS 2 ? CHAIN GUIDE 3 – CRANKSHAFT TIMING MARKS 4 – CRANKSHAFT SPROCKET 5 – CHAIN TENSKJNER ARM 6 – CHAIN TENSIONER 7 – CAMSHAFT TIMING MARK 8 – INTAKE CAMSHAFT SPROCKETS 9 – CHAIN GUIDES 10 – WATER PUMP SPROCKET 7. Loosely position left side camshaft sprocket over camshaft hub. 8. Align timing (plated) link tq the crankshaft sprocket timing mark (Fig. 122). 9. Position primary chain onto water pump drive sprocket. 10. Align right camshaft sprocket timing mark to the timing (plated) link on the timing chain (Fig. 122) and loosely position over camshaft hub. 11. Verify that all chain timing (plated) links are properly aligned to the timing marks on all sprockets (Fig. 122). 12. Install left side lower chain guide and tensioner arm (Fig. 120). Tighten attaching bolts to 28 Nm (250 in. lbs.). NOTE: Inspect oil ring on chain guide access plug before installing. Replace O-ring as necessary. 13. Install chain guide access plug to left side cylinder head (Fig. 120). Tighten plug to 20 Nm (15 ft lbs.)

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Removal 1. Release fuel pressure. See FUEL PRESSURE RELEASE under REMOVAL & INSTALLATION. Disconnect negative battery cable. Drain coolant from radiator and cylinder block. Remove radiator shroud and fan. Remove accessory drive belts. Remove spark plugs. 2. Remove distributor cap. Set cylinder No. 1 at TDC of compression stroke (rotate crankshaft until marks on crankshaft pulley and front cover align, and distributor rotor points to spark plug wire No. 1 on cap). Remove distributor. Remove power steering pump, idler pulley and power steering pump brackets. 3. Remove A/C compressor idler pulley (if equipped). Remove crankshaft pulley. Remove oil pump and oil pump drive spindle from right side of front cover. Remove oil pan. See OIL PAN under REMOVAL & INSTALLATION. Remove front cover. 4. Remove chain tensioner, chain guides, timing chain and sprocket. Remove oil thrower, oil pump drive gear and crankshaft sprocket. Inspection Check chain roller links. Replace chain if roller links are cracked or worn. Installation 1. Install crankshaft sprocket with sprocket teeth toward front of engine, and shoulder toward rear of engine. Install oil pump drive gear with gear teeth toward front of engine, and shoulder toward rear of engine. Install oil thrower. 2. Ensure cylinder No. 1 is at TDC of compression stroke. Camshaft knockpin (or keyway) and crankshaft sprocket keyway should be at 12 o’clock position. See Fig. 7 . Install timing chain, aligning timing chain links with timing mark on each sprocket. 3. Tighten camshaft sprocket bolt to specification. See TORQUE SPECIFICATIONS . Install chain guide. Install chain tensioner. Apply lithium grease to sealing lip of front cover oil seal. Apply a .08-.12″ (2-3 mm) diameter bead of sealant to front cover. 4. Install front cover, ensuring front cover-to-cylinder block oil seals are in position on right sealing surface of cylinder block. Apply sealant to rubber plugs for cylinder head cover. See Fig. 4 . Install rubber plugs. Install cylinder head cover. Tighten bolts to specification. 5. Install oil pan. See OIL PAN under REMOVAL & INSTALLATION. Align punch mark on oil pump drive spindle with oil hole on oil pump. See Fig. 8 . Using NEW gasket, install oil pump and drive spindle assembly into front cover. Ensure upper end of drive spindle is correctly positioned. Install distributor, ensuring rotor is correctly positioned. To complete installation, reverse removal procedure.