GM Full-Size Trucks 1980-1987 Repair Guide

Timing Chain and Sprockets

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REMOVAL & INSTALLATION



Gasoline V8 and V6

See Figures 1 and 2

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the radiator core.
  4.  
  5. Remove the water pump.
  6.  
  7. Remove the harmonic balancer and the crankcase front cover. This will allow access to the timing chain.
  8.  
  9. Crank the engine until the timing marks on both sprockets are nearest each other and in line between the shaft centers.
  10.  
  11. Take out 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. The chain comes off with the camshaft gear.
  12.  
  13. A gear puller will be required to remove the crankshaft gear.
  14.  

To install:
  1. Without disturbing the position of the engine, mount the new crankshaft gear on the shaft, and mount the chain over the camshaft gear.
  2.  
  3. 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.
  4.  
  5. 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. 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.



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Fig. Fig. 1: V6 262 timing sprocket alignment



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Fig. Fig. 2: Timing sprocket alignment, 1980 and later gasoline V8's

8-350 Diesel

See Figure 3

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the crankshaft pulley, the harmonic balancer and the front cover.
  4.  
  5. Align the timing marks on the cam and crankshaft.
  6.  
  7. Remove the oil slinger and camshaft sprocket retaining nut.
  8.  
  9. 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.
  10.  
  11. Remove the timing chain and camshaft sprocket.
  12.  

To install:
  1. The fuel pump eccentric is behind the crankshaft sprocket, and may be removed if necessary.
  2.  
  3. Install the key in the crankshaft, if removed. Install the fuel pump eccentric, if removed.
  4.  
  5. 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.
  6.  

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 Engine Electrical .
  4.  
  5. Install the front cover, harmonic balancer, and the crankshaft pulley.
  6.  



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Fig. Fig. 3: 350 diesel timing sprocket alignment

8-379 Diesel

See Figure 4

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the front cover.
  4.  
  5. Remove the bolt and washer attaching the camshaft gear. Remove the injection pump gear.
  6.  
  7. Remove the camshaft sprocket, timing chain, and crankshaft sprocket as a unit.
  8.  

To install:
  1. Install, the cam sprocket, timing chain and crankshaft sprocket as a unit, aligning the timing marks on the sprockets as shown in the illustration.
  2.  
  3. Rotate the crankshaft 360 degrees so that the camshaft gear and the injection pump gear are aligned as shown in the illustration (accompanying the 379 Diesel Front Cover Removal Procedure).
  4.  
  5. Install the front cover. The injection pump must be retimed since the timing chain assembly was removed. See Engine Performance & Tune-up for this procedure.
  6.  



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Fig. Fig. 4: 379 diesel timing chain assembly

 
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