Loosening sequences

• Where more than one bolt/nut secures a component, loosen each fastener evenly a little at a time. In this way, not all the stress of the joint is held by one fastener and the components are not likely to distort.

• If a tightening sequence is provided, work in the REVERSE of this, but if not, work from the outside in, in a criss-cross sequence (see illustration 4.4).

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When slackening, work from the outside inwards

Tightening sequences

• Ifa component is held by more than one fastener it is important that the retaining bolts/nuts are tightened evenly to prevent uneven stress build-up and distortion of sealing faces. This is especially important on high-compression joints such as the cylinder head.

• A sequence is usually provided by the manufacturer, either in a diagram or actually marked in the casting. If not, always start in the centre and work outwards in a criss-cross pattern (see illustration 4.5).Start off by securing all bolts/nuts finger-tight, then set the torque wrench and tighten each fastener by a small amount in sequence until the final torque is reached. By following this practice,

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Set the torque wrench index mark to the setting required, in this case 12 Nm

Or by marking the angle on the surrounding component

When tightening, work from the inside outwards

ref.14 Tools and Workshop Tips

the joint will be held evenly and will not be distorted. Important joints, such as the cylinder head and big-end fasteners often have two- or three-stage torque settings.

Applying leverage

• Use tools at the correct angle. Position a socket wrench or spanner on the bolt/nut so that you pull it towards you when loosening. If this can't be done, push the spanner without curling your fingers around it (see illustration 4.6)- the spanner may slip or the fastener loosen suddenly, resulting in your fingers being crushed against a component.

4.6 If you can't pull on the spanner to loosen a fastener, push with your hand open

• Additional leverage is gained by extending the length of the lever. The best way to do this is to use a breaker bar instead of the regular length tool, or to slip a length of tubing over the end of the spanner or socket wrench.

• If additional leverage will not work, the fastener head is either damaged or firmly corroded in place (see Fasteners).

5 Bearings

Date: 2016-01-14; view: 1145