CTS 2003-2005

Timing Chain & Sprockets

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Removal & Installation



3.1L & 3.4L Engines
  1. Remove the timing chain front cover using the procedures found in this section.
  2.  
  3. Rotate the crankshaft until the timing marks in the following locations are aligned:
    1. The camshaft alignment is at 3 o'clock.
    2.  
    3. The timing chain damper and crankshaft sprocket marks are aligned at 12 o'clock.
    4.  
    5. The crankshaft key is at 11 o'clock.
    6.  
    7. The timing chain damper and camshaft sprocket locator hole are next to each other.
    8.  

  4.  
  5. Remove the camshaft sprocket bolt and remove the sprocket along with the timing chain.
  6.  
  7. A puller is recommended to draw the crankshaft sprocket from the nose of the crankshaft. Use care if using substitutes. Be careful not to mar the balancer bolt threads in the crankshaft.
  8.  
  9. If desired, remove the two bolts and remove timing chain dampener. The damper is the roughly triangular piece bolted to the block between the crankshaft sprocket and the camshaft sprocket. Look for small timing mark alignment notches in the top and bottom.
  10.  



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Fig. The camshaft and crankshaft timing marks MUST be properly aligned-3.1L and 3.4L (VIN E) engines



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Fig. Special tools are recommended for removing and installing the timing chain sprockets-3.1L and 3.4L (VIN E) engines

To install:

  1. Clean all parts well. Inspect the sprockets for wear. While individual parts may be replaced, in actual practice, a timing chain is usually installed with new camshaft and crankshaft sprockets, as a set. If removed, install the timing chain dampener.
  2.  
  3. A special tool, J 38612, or equivalent, is recommended for installing the crankshaft sprocket. It threads into the nose of the crankshaft and the sprocket is pressed in. Use care is using substitutes. Before installation, coat the thrust face (back side) of the crankshaft sprocket with GM EOS #1052367, or equivalent engine assembly lube.
  4.  
  5. Align the crankshaft timing mark at 12 o'clock to the timing mark on the bottom of the chain dampener.
  6.  
  7. Hold the camshaft sprocket and drape the timing chain over the sprocket. With the chain hanging down, install the chain to the crankshaft gear.
  8.  
  9. Align the timing mark on the camshaft gear (centerline of the locator hole) at 6 o'clock with the timing mark on the top of the chain dampener.
  10.  
  11. Align the dowel in the camshaft with the dowel hole in the camshaft sprocket (should be at 3 o'clock).
  12.  
  13. Draw the camshaft sprocket onto the camshaft using the mounting bolt.
  14.  
  15. Coat the crankshaft and camshaft sprocket with engine oil. Install the camshaft sprocket retaining bolt and torque to 81 ft. lbs. (110 Nm).
  16.  
  17. Install the engine front cover using the procedures found in this section.
  18.  

3.4L (VIN X) Engine

The camshaft drive is a two-stage system. The first stage is a chain and sprocket arrangement that transfers power from the crankshaft to an intermediate shaft. The intermediate shaft then transfers power to the camshafts by means of a cogged belt and the second stage of the system. To service the chain and sprockets, the first stage of the system, (GM calls it the Cam Inter Drive Shaft Chain and Sprockets), use the following procedure.

  1. Remove the engine front cover using the procedures found in this section.
  2.  
  3. Retract the timing chain tensioner and remove the tensioner bolts.
  4.  
  5. Raise and safely support the vehicle.
  6.  
  7. Remove the timing chain, the crankshaft sprocket and the intermediate shaft sprocket as an assembly. A gear puller may be required. If the intermediate gear does not slide off easily with the timing chain, rotate the crankshaft back and forth to help loosen the tight fit.
  8.  
  9. Remove the timing chain tensioner.
  10.  
  11. Inspect the crankshaft alignment key for burrs or marks that could affect assembly.
  12.  



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Fig. Cam Inter Drive Shaft Chain and Sprockets-3.4L (VIN X) engine



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Fig. View of the timing chain and related components with the front cover removed-3.4L (VIN X) engine



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Fig. Special tools must be used . . .



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Fig. . . . to remove the timing chain, crankshaft sprocket and intermediate shaft sprocket-3.4L (VIN X) engine



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Fig. This shop-made tool is used to retract the chain tensioner so it can be pinned in place-3.4L (VIN X) engine



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Fig. Slide the sprocket and chain on the shafts, maintaining the proper alignment-3.4L (VIN X) engine



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Fig. The crankshaft sprocket must be pressed on using this special tool-3.4L (VIN X) engine

To install:

  1. Make sure the crankshaft key is installed and fully seated, and that the chain tensioner is installed and the blade retracted. Use the following procedures:
    1. Inspect the timing chain tensioner for signs of wear.
    2.  
    3. DO NOT use a sharp or narrow point or nylon blade to retract the timing chain tensioner. A shop-made retracting tool, described here, must be used to retract the blade.
    4.  
    5. Install the timing chain tensioner on the engine block. Use the upper attaching hole as the primary locator. Hand-tighten the tensioner retaining bolts.
    6.  
    7. Install the slotted hole bolt and tighten to 18 ft. lbs. (25 Nm). Install the other retaining bolts. Tighten the intermediate drive shaft retaining bolts to 18 ft. lbs. (25 Nm).
    8.  
    9. Fabricate a tool to retract the tensioner. Bend a 12-inch length of 1/8-inch welding rod or equivalent, in half, to a U-shape, leaving a 1 inch gap between the two ends. Make two more U-shaped bends 1-inch from each end.
    10.  
    11. Using the tool, retract the shoe on the timing chain tensioner. Compress the tensioner spring and insert a cotter pin, a nail or equivalent pin strong enough to keep the timing chain tensioner spring compressed.
    12.  
    13. Lightly oil or apply lithium grease to the chain contact surfaces of the tensioner nylon pad and blade.
    14.  

  2.  
  3. With the chain tensioner retracted, slip both sprockets and the chain over the proper shaft and engage the slot in the key. The intermediate shaft may move against the rear cover. Slide the sprocket and chain on the shafts maintaining the parallel alignment of the sprockets.
  4.  
  5. Make sure that the rubber and the tension blade of the tensioner does not become caught, misaligned or dislodged.
  6.  
  7. The larger chamfer and the counterbore of the crankshaft sprocket are installed toward the crankshaft. The intermediate sprocket spline sockets are installed away from the case. The crankshaft sprocket must be pressed on for the final 3 / 8 inch (8mm) or so to the seated position. GM recommends their tool J 38612.
  8.  
  9. Verify that the timing is maintained.
  10.  
  11. Pull the retaining pin from the tensioner
  12.  
  13. Install the front cover using the procedures found in this section.
  14.  

3.5L Engine

The four overhead camshafts are driven by three separate 8mm, single-row, fine pitch chains. The primary drive chain connects the crankshaft with both large intake camshaft sprockets, the balance shaft sprockets and the intermediate shaft sprocket. The exhaust camshafts are driven by the secondary chains which are short chains from the intake camshafts. Primary camshaft timing chain service is covered here. For secondary chain and sprocket service, please see Camshaft Removal and Installation in this section. Careful work will be required to line up all of the timing marks. As with most valvetrain-related service on this engine, Special Tools J 42038 Camshaft Holding Fixtures are required for this procedure.

  1. Remove the camshaft covers using the procedures found in this section.
  2.  
  3. Install Special Tools J 42038, or their exact equivalent Camshaft Holding Fixtures onto the camshafts. This is important because the camshafts will rotate from valve spring pressure when the timing chain tension is released.
  4.  
  5. Remove the engine front cover using the procedures found in this section.
  6.  
  7. Remove the front engine lift bracket and the camshaft position sensor next to it
  8.  
  9. Remove the right side (rear) exhaust camshaft sprocket bolt to allow clearance for the right cylinder head chain guide.
  10.  
  11. Remove the four chain guide access plugs located in the cylinder heads. Note the O-ring seal on each access plug.
  12.  
  13. Loosen both primary timing chain tensioner bolts. Remove the lower tensioner bolt allowing the tensioner to swing downward and expand. This will release tension on the chain. Now remove the upper bolt and remove the primary drive chain tensioner.
  14.  
  15. Remove the primary timing chain tensioner shoe retaining bolt and remove the tensioner shoe by pushing the guide downward slightly and then pulling it up through the cylinder head.
  16.  
  17. Remove the primary timing chain from the right side (rear) camshaft sprocket and allow the chain to fall into the oil pump area of the engine block. Remove the chain from the engine.
  18.  



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Fig. Exploded view of the primary timing chain and related components-3.5L (VIN H) engine



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Fig. Remove the chain access plugs. Make sure the O-rings are in good condition-3.5L (VIN H) engine



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Fig. All of these timing marks and marked (darkened) chain links must be aligned-3.5L (VIN H) engine

To install:

  1. Clean all parts well. Remove all dirt and old sealer from gasket sealing surfaces. Use care not to gouge the soft light alloy parts.
  2.  
  3. Examine the timing chain. There should be some links chemically darkened to distinguish them from the other links. They will be important in setting up the engine timing. With the Camshaft Holding Fixtures still securely in place, install the timing chain to the engine. Make sure the darkened timing links on the timing chain are facing toward the engine. An open-end wrench can be used on the hex-shape formed into the camshaft to provide minor adjustments to the secondary sprocket position.
  4.  
  5. When installing the primary timing chain, you must set the base engine timing. Base engine timing is set with cylinder #1 (right side, rear, forward cylinder) at Top Dead Center (TDC) starting the intake stroke and with the correct camshaft to balance shaft to crankshaft relationship. To set the correct base engine timing, proceed as follows:
    1. Rotate the crankshaft until cylinder #1 is at TDC and crankshaft sprocket timing mark is at the 4 o'clock position. A Special Tool, J 43032 Crankshaft Rotation Socket, is recommended since it may be difficult to turn the crankshaft since the crankshaft dampener has already been removed for front cover removal. Use care is using substitutes.
    2.  
    3. Rotate the balance shaft until its timing mark is at the 5 o'clock position.
    4.  

  6.  
  7. Verify that the timing chain has been installed with the darkened timing links on the timing chain facing toward the engine.
  8.  
  9. Center the timing mark on the left side (front) intake camshaft between the paired darkened timing links and wrap the chain around the sprocket. Allow the remainder of the chain to drop into the crankcase area once the timing mark is aligned.
  10.  
  11. Fabricate a hook out of wire and feed it down through the right side (rear) cylinder head. Use the hook to pull the remainder of the timing chain up to the right intake camshaft sprocket.
  12.  
  13. While pulling the timing chain up to the right cylinder head, align the marked timing chain links with the balance shaft and crankshaft sprockets.
  14.  
  15. Wrap the timing chain around the right intake camshaft sprocket and align the marked links with the sprocket's timing mark.
  16.  
  17. Make sure all the timing marks are properly aligned with the marked timing chain links.
  18.  
  19. When satisfied with the timing chain fit and the engine timing, install the timing chain tensioner shoe. To install the retaining bolt, use the access hole in the cylinder head. Tighten the bolt to 22 ft. lbs. (30 Nm).
  20.  
  21. Collapse the timing chain tensioner using the following procedure:
    1. Rotate the ratchet release lever counterclockwise and hold.
    2.  
    3. Collapse the tensioner shoe and hold.
    4.  
    5. Release the ratchet lever and slowly release the pressure on the shoe.
    6.  

  22.  
  23. As the ratchet moves to its first click, hold the tensioner shoe inward. Insert a pin through the hole in the release lever. The locked ratchet mechanism should hold the shoe in a collapsed position.
  24.  
  25. Making sure the tensioner release lever faces toward you, install the tensioner and the retaining bolts. Tighten the bolts to 18 ft lbs. (25 Nm).
  26.  
  27. Verify once again that all the timing marks are properly aligned. Make any adjustments as necessary.
  28.  
  29. Remove the pin holding the tensioner to tighten any slack in the timing chain.
  30.  
  31. Verify that each of the four chain guide access plugs has an O-ring installed. Install the plugs and snug down to 44 inch lbs. (5 Nm).
  32.  
  33. Install the front engine lift bracket. Tighten the hex-head bolt to 37 ft. lbs. (50 Nm) and the internal drive bolt to 18 ft. lbs. (25 Nm).
  34.  
  35. Install the camshaft position sensor.
  36.  
  37. Remove the camshaft holding fixtures from both banks of camshafts.
  38.  
  39. Verify once again that all the timing marks are properly aligned.
  40.  
  41. Install the camshaft covers using the procedures found in this section.
  42.  
  43. Install the engine front cover using the procedures found in this section.
  44.  

3.8L Engine

NOTE
It is good practice to set the engine to Top Dead Center (TDC), No. 1 cylinder (left side, or front bank, front cylinder) on the compression stroke (firing position) before removing the timing chain. In this way, if the engine is inadvertently turned, you can always come back to the original setting.

  1. Remove the engine front cover using the procedures found in this section.
  2.  
  3. Align the timing marks on the sprockets so that they are as close as possible. The cam drive sprocket should be at the 6 o'clock position and the crankshaft sprocket should be at 12 o'clock.
  4.  
  5. Remove the timing chain dampener.
  6.  
  7. Before removing the timing chain, check for wear. Inspect the timing chain for overall in and out movement. Movement should not exceed 1 inch (25mm).
  8.  
  9. Remove the camshaft sprocket bolts and remove the sprocket and timing chain.
  10.  


NOTE
If the sprocket does not come off easily, a light blow on the lower edge of the sprocket with a plastic mallet should dislodge the sprocket.

  1. Remove the crankshaft sprocket.
  2.  



Click image to see an enlarged view

Fig. Timing chain, sprockets and timing mark alignment-3.8L engines

To install:

  1. Clean all parts well. Inspect the chain and sprockets for wear. While it may be possible to replace individual parts, in actual practice, timing chains and sprockets are normally replaced as a set.
  2.  
  3. If the crankshaft has been turned, rotate the crankshaft so that the number one piston is at TDC. Turn the camshaft so that, with the sprocket temporarily installed, the timing mark is straight down (6 o'clock position).
  4.  
  5. Install the crankshaft sprocket. Drape the timing chain over the cam drive sprocket and install the sprocket with the timing marks on the two sprockets as close to each other as possible.
  6.  
  7. Install the camshaft sprocket bolt. A new replacement bolt is recommended. Torque to 74 ft. lbs. (100 Nm) then turn an additional 90 degrees.
  8.  


NOTE
This bolt is designed to permanently stretch when tightened. The correct part number fastener must be used to replace this type of fastener. Do not use a bolt that is stronger in this application. If the correct bolt is not used, the parts will not be tightened correctly. The system may be damaged.

  1. Install the chain dampener and tighten the bolt to 16 ft. lbs. (22 Nm).
  2.  


WARNING
Rotate the crankshaft two revolutions and check the timing marks. Ensure that, after two full turns, the timing marks come back into alignment.

  1. Install the engine front cover using the procedures found in this section.
  2.