Astro, Safari 1997-2005

Timing Chain & Sprockets

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NOTE
The following procedure requires the use of the Crankshaft Sprocket Removal tool No. J-5825-A and the Crankshaft Sprocket Installation tool No. J-5590.

  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Remove the front cover from the engine.
  4.  
  5. Rotate the crankshaft until the No. 4 cylinder is on the Top Dead Center (TDC) of its compression stroke and the camshaft sprocket mark aligns with the mark on the crankshaft sprocket (facing each other at a point closest together in their travel) and in line with the shaft centers.
  6.  
  7. Remove crankshaft Position (CKP) sensor reluctor ring, if equipped.

    Click image to see an enlarged view

    Fig. Timing mark alignment-4.3L engine

  8.  
  9. Remove camshaft sprocket-to-camshaft nut and/or bolts.
  10.  
  11. Remove camshaft sprocket (along with the timing chain). If the sprocket is difficult to remove, use a plastic mallet to bump the sprocket from the camshaft.
    NOTE
    The camshaft sprocket (located by a dowel) is lightly pressed onto the camshaft and should come off easily. The chain comes off with the camshaft sprocket.

  12.  
  13. If necessary use J-5825-A crankshaft sprocket removal tool to free the timing sprocket from the crankshaft.
  14.  
  15. If necessary, remove the crankshaft sprocket key.
  16.  

To install:

  1. Inspect the timing chain and the timing sprockets for wear or damage, replace the damaged parts as necessary.

    Click image to see an enlarged view

    Fig. Removal (top) and installation of the crankshaft timing gear

  2.  
  3. Using a putty knife, clean the gasket mounting surfaces. Using solvent, clean the oil and grease from the gasket mounting surfaces.
  4.  
  5. Install crankshaft sprocket key, if removed.
  6.  
  7. Install crankshaft sprocket onto the crankshaft using J-5590 crankshaft sprocket installation tool and a hammer without disturbing the position of the engine.
    NOTE
    During installation, coat the thrust surfaces lightly with Molykote® or an equivalent pre-lube.

  8.  
  9. Install timing chain over the camshaft sprocket. Arrange the camshaft sprocket in such a way that the timing marks will align between the shaft centers and the camshaft locating dowel will enter the dowel hole in the cam sprocket.
  10.  
  11. Install timing chain under the crankshaft sprocket, then place the cam sprocket, with the chain still mounted over it, in position on the front of the camshaft.
  12.  
  13. Tighten camshaft sprocket-to-camshaft retainers to 18 ft. lbs. (25 Nm).
  14.  
  15. With the timing chain installed, turn the crankshaft two complete revolutions, then check to make certain that the timing marks are in correct alignment between the shaft centers.
  16.  
  17. Install CKP sensor reluctor ring, if equipped.
  18.  
  19. Install timing cover.
  20.  

 
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