GM Full-Size Trucks 1970-1979 Repair Guide

Timing Chain And Sprockets

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REMOVAL & INSTALLATION



Gasoline V6 and V8 Engines

See Figures 1, 2, 3, 4, 5 and 6



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Fig. Fig. 1: View of the timing chain and sprocket assemblies, after the cover is removed



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Fig. Fig. 2: Remove the three camshaft sprocket-to-camshaft retaining bolts



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Fig. Fig. 3: Remove the timing chain and camshaft sprocket assembly



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Fig. Fig. 4: Assemble a suitable gear puller to the crankshaft gear ...



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Fig. Fig. 5: ... then remove the gear from the crankshaft



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Fig. Fig. 6: Timing sprocket alignment - gasoline engines

  1. Remove the radiator core, water pump, the harmonic balancer and the crankcase front cover. This will allow access to the timing chain.
  2.  
  3. Crank the engine until the timing marks on both sprockets are nearest each other and in line between the shaft centers.
  4.  
  5. Unfasten the three bolts that hold the camshaft gear to the camshaft. This gear is a light press fit on the camshaft and will come off easily. On others it may require a puller. It is located by a dowel.
  6.  
  7. The chain will come off with the camshaft gear.
  8.  
  9. A gear puller will be required to remove the crankshaft gear. Without disturbing the position of the engine, mount the new crankshaft gear on the shaft, and mount the chain over the camshaft gear. Arrange the camshaft gear in such a way that the timing marks will line up between the shaft centers and the camshaft locating dowel will enter the dowel hole in the cam sprocket.
  10.  

To install:
  1. Installation is the reverse of the removal procedure.
  2.  
  3. Place the cam sprocket, with its chain mounted over it, in position on the front of the car and pull up with the three bolts that hold it to the camshaft.
  4.  
  5. After the gears are in place, turn the engine two full revolutions to make certain that the timing marks are in correct alignment between the shaft centers.
  6.  

When installing the timing chain, install the sprockets with the timing marks facing each other; this position is TDC of the No. 6 cyl. (V8) or No. 4 cyl. (V6). To locate the TDC of the No. 1 cyl., turn the crankshaft one full revolution, the camshaft timing mark will now be at the top of the sprocket.

  1. Install the timing chain front cover, as outlined earlier in this section.
  2.  

350 Diesel Engine

See Figure 7



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Fig. Fig. 7: Timing mark alignment - 350 diesel engine

  1. Remove the crankshaft pulley, the harmonic balancer and the front cover as previously detailed.
  2.  
  3. Align the timing marks on the cam and crankshaft.
  4.  
  5. Remove the oil slinger and camshaft sprocket retaining nut.
  6.  
  7. Remove the crankshaft sprocket. The sprocket-to-crankshaft fit is such that a puller may be necessary. If possible, the crankshaft key should be removed before using the puller. If this is not possible, align the puller so that the fingers of the tool do not overlap the end of the key when the sprocket is removed. The keyway is machined only part way in the crankshaft sprocket, and breakage can occur if the sprocket is improperly removed.
  8.  
  9. Remove the timing chain and camshaft sprocket.
  10.  
  11. The fuel pump eccentric is behind the crankshaft sprocket, and may be removed if necessary.
  12.  
  13. Install the key in the crankshaft, if removed. Install the fuel pump eccentric, if removed.
  14.  
  15. Install the camshaft sprocket, crankshaft sprocket, and the timing chain together, with the timing marks aligned. Tighten the camshaft sprocket retaining bolt to 65 ft. lbs. (88 Nm).
  16.  

When the two timing marks are in alignment and closest together, the No. 6 cylinder is at TDC. To obtain TDC for No. 1 cylinder, slowly rotate the crankshaft one full revolution. This will move the camshaft sprocket timing mark to the top. No. 1 cylinder will then be at TDC.

  1. Install the oil slinger.
  2.  
  3. The injection pump must be re-timed. Refer to Routine Maintenance .
  4.  
  5. Install the front cover, harmonic balancer, and the crankshaft pulley.
  6.  

 
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