GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Balance Shaft

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The crankshaft is counterbalanced by the flywheel, the crankshaft pulley, and weights cast into the crankshaft. Additional counter balancing is obtained from the balance shaft, which rides in the block above the camshaft and is driven by the camshaft.

Removal & Installation 3.8L Engine



This procedure requires several special tools. The are as follows:



Slide Hammer
 
Dial Indicator
 
Torque Angle Meter
 
Bearing Remover/Installer
 
Balance Shaft Installer
 

See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Balance shaft service and special tool usage

  1. Remove the flywheel, as outlined in this section.
  2.  
  3. Remove the intake manifold
  4.  
  5. Remove the lifter guide retainer.
  6.  
  7. Remove the front cover.
  8.  
  9. Remove the balance shaft drive gear bolt.
  10.  
  11. Remove the camshaft sprocket and timing chain.
  12.  
  13. Remove the balance shaft retainer bolts, retainer and gear. Remove the balance shaft using the special tool J 6125-B.
  14.  
  15. Remove the balance shaft rear plug, and the rear bearing using the special removal tool.
  16.  
  17. The balance shaft and both bearings are serviced as a complete package. Use only the correct tools for bearing and shaft installation.
  18.  

Inspect the balance shaft drive gear and the camshaft drive gear for nicks and burrs.See Figures 2, 3 and 4

Click image to see an enlarged view

Fig. Fig. 2: The balance runs from one end of the block to the other



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Fig. Fig. 3: Closer view of the balance shaft. Note it's irregular and asymmetrical shape



Click image to see an enlarged view

Fig. Fig. 4: View of the bearings that the shaft rides on in the front of the block.

To install:
  1. Dip the bearings in clean engine oil before installation. Install the bearing with the rolled edge facing into the engine and the manufacturer's markings facing the flywheel side.
  2.  
  3. Install the balance shaft rear bearing using the special installation tool.
  4.  
  5. Install the balance shaft into the block using the special installation tool.
  6.  
  7. Temporarily install the balance shaft bearing retainer and bolts.
  8.  
  9. Apply a suitable thread lock compound to bolt threads.
  10.  
  11. Install the balance shaft drive gear and bolt. Tighten the bolt, using the torque angle meter, to 15 ft. lbs. (20 Nm), plus an additional 35° rotation.
  12.  
  13. Install the balance shaft rear plug.
  14.  
  15. Measure the balance shaft endplay. It should be 0.000-0.008 in. (0.000-0.203mm).
  16.  
  17. Measure the balance shaft radial play at both the front and rear:
    1. Front radial play should be 0.000-0.0011 inch (0.000-0.028mm)
    2.  
    3. Rear radial play should be 0.0005-0.0047 inch (0.0127-0.119mm).
    4.  

  18.  
  19. Turn the camshaft so that, with the camshaft sprocket temporarily installed, the timing mark is straight down.
  20.  
  21. With the camshaft sprocket and the camshaft gear removed, turn the balance shaft so that the timing mark on the gear points straight down.
  22.  
  23. Install the camshaft gear.
  24.  
  25. Align the marks on the balance shaft gear and the camshaft gear by turning the balance shaft.
  26.  
  27. Turn the crankshaft so that number one piston is at top dead center.
  28.  
  29. Install the timing chain and camshaft sprocket.
  30.  
  31. Measure gear lash at four places, every 90° turn. Lash should be 0.002 to 0.005 inch (0.050 to 0.127mm).
  32.  
  33. Install the balance shaft front bearing retainer and bolts, tighten to 22 ft. lbs. (30 Nm).
  34.  
  35. Install the front cover.
  36.  
  37. Install the lifter guide retainer.
  38.  
  39. Install the intake manifold.
  40.  
  41. Install the flywheel, tighten the bolts to 11 ft. lbs. (15N.m), plus an additional 50° rotation.
  42.  
  43. Complete the engine installation, as outlined earlier in this section.
  44.  

 
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