GM Firebird 1967-1981 Repair Guide

Timing Chain or Gear

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REMOVAL & INSTALLATION OHV 230 and 250 Engines



The 6-cylinder camshaft is gear driven. To remove the camshaft gear, remove the camshaft and press the gear off.


CAUTION
The thrust plate must be positioned so that the woodruff key in the shaft does not damage it when the shaft is pressed out of the gear. Support the hub of the gear or the gear will be seriously damaged.

The crankshaft gear may be removed with a gear puller while in place in the block.

231 Engine See Figure 1

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Fig. Fig. 1: Identification of the timing chain and gear components used on 231 V6 engines

  1. Remove the timing chain cover.
  2.  
  3. Before removing anything else, make sure the timing marks on the crankshaft and camshaft sprockets are aligned. This will greatly ease reinstallation of parts.
  4.  
  5. It is not necessary to remove the timing chain tensioners unless they are worn or damaged.
  6.  
  7. Remove the front crankshaft oil slinger.
  8.  
  9. Remove the bolt and the special washer that hold the camshaft distributor drive gear and fuel pump eccentric at the forward end of the camshaft. Remove the eccentric and the gear from the camshaft.
  10.  
  11. Using a pair of large prytools, alternately pry the camshaft sprocket, then the crankshaft sprocket forward until the camshaft sprocket is free.
  12.  
  13. After the camshaft sprocket and chain are removed, finish prying the crankshaft sprocket off the crankshaft.
  14.  

To install:
  1. If the engine has not been disturbed, proceed to Step 11.
  2.  
  3. If the engine has been disturbed, turn the crankshaft so that the No. 1 piston is at top dead center.
  4.  
  5. Temporarily install the sprocket key and the camshaft sprocket on the camshaft. Turn the camshaft so that the index mark of the sprocket is pointing downward. Remove the key and the sprocket from the camshaft.
  6.  
  7. Assemble the timing chain and sprockets. Install the keys, sprockets, and chain assembly on the crankshaft and camshaft so that the index marks of both the sprockets are aligned. It will be necessary to hold the chain tensioners out of the way while installing the timing chain and sprocket assembly.
  8.  
  9. Install the front oil slinger on the crankshaft with the concave side toward the front of the engine.
  10.  
  11. Install the fuel pump eccentric with the oil groove forward.
  12.  
  13. Install the distributor drive gear on the camshaft.
  14.  
  15. Install the front cover.
  16.  

265, 301, 305, 326, 350, 400, 403 and 455 Engines See Figures 2 through 7

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Fig. Fig. 2: Before removing the timing chain from 1967-78 8-cylinder engines, align the timing marks on the gears as indicated



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Fig. Fig. 3: Prior to removing the timing chain and gears, rotate the timing marks until the No. 6 cylinder at TDC is attained (toward each other) 1979-81 8-cylinder engines



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Fig. Fig. 4: Rotate the crankshaft until the timing marks (arrows) align as shown



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Fig. Fig. 5: To check timing chain play, push the chain in ...



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Fig. Fig. 6: ... then pull the chain out and measure the difference



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Fig. Fig. 7: If necessary, remove the chain by removing the 3 camshaft bolts (arrows)


CAUTION
When draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

These models are equipped with a timing chain. To replace the chain, remove the radiator core, water pump harmonic balancer, and the crankcase front cover. This will allow access to the timing chain. Crank the engine until the zero marks punched on both sprockets are closest to one another and in line between the shaft centers. Then, 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 readily. It is located by a dowel.

The chain comes off with the camshaft gear.

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, mount the new crank gear on the shaft, then 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.

Place the cam sprocket, with its chain mounted over it, in position on the front of the camshaft 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.

 
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