Sunday, May 22, 2011

Installing Cylinder-Heads

Fig. 3.11

Installing a Cylinder-head is, generally, the reverse procedure to removal.  Following are related points:
1.   Before installing Cylinder-head, the surfaces of both the Cylinder-head and cylinder-block must be clean.  The bolts and threads into cylinder-block must also be clean.
2.   A new Cylinder-head gasket must be used.  The gaskets are ready and sealer is not usually used. Aligning studs can be installed in two diagonally opposite holes to keep the gasket in place.

  • Most gaskets will only fit one way, but some have the top identified, as shown in figure 3.11

2.     Cylinder-one bolts must be tightened in the correct sequence and the correct torque. Incorrect tightening can cause head and block distortion, gasket leakage or bolt failure.

Tightening Cylinder-Head bolts
Fig. 3.12
Spiral tightening sequence is often used for tightening Cylinder-Head bolts. This starts with the bolts at the center of the head and proceeds in a spiral-pattern so that the bolts are tightened progressively outwards from the center. Another sequence starts at the center and then follows a diagonal pattern towards the ends (figure 3.12).
Cylinder-Head bolts can be tightened to a specified torque using a torque wrench. They are tightened in three steps, following the pattern, with the torque being increased each time until the specified torque is reached.

Fig. 3.13 (a)
·   Cast iron Cylinder-heads can be re-tightened when hot and Aluminum heads can be re-tightened when cold, although the Cylinder-Heads gaskets that are now used, re-tightening is not considered necessary.

Torque-angle tightening
With many Cylinder-Heads, the bolts are tightened using the torque-angle method. With this method, the bolts are tightened to a specified torque and then tightened further by turning to the specified angle or angles. A torque-angle wrench can be used, on the bolt head can be used, or the bolt head can be marked to identify its position.
Fig. 3.13 (b)
Following is an example of a torque-angle tightening, but there are variations of both methods and specifications.  The relevant service manual should be consulted for the recommendations for a particularly vehicle.

Figure 3.13 illustrates the method of tightening.  The bolts are tightened in three steps as shown:
1. First step – figure 3.13 (a). A torque wrench is used to tighten the bolts to a torque of 30 newton meters.  This is done progressively and to a specified sequence.

2. Second step – figure of 3.13 (b).  When tightened, the front of each bolt head is marked. A normal wrench is then used to turn the bolts through an angle of 90°.

3. Third step – figure 3.13 (c). The bolts are tightened further by turning them an additional angle 
    of 90°. 

Fig. 3.13 (c)
·       The mark on the bolt head would have turned 180° and should now
      face the rear of the cylinder head.

Installation of the manifolds
Manifold bolts should be tightened gradually, in the correct
sequence, and to the correct torque. This applies to any casting.
An example of an exhaust manifold is shown in figure 3.14, near 
the bolts are tightened from the center towards that ends. Intake
manifolds will also have a similar type of sequence. 

Fig. 3.14

See Installing valve mechanisms>>>>>

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