Discovery 2. Manual - part 4

GENERAL INFORMATION

03-9

Joints and Joint Faces

General
Fit joints dry unless specified otherwise.

Always use the correct gaskets as specified.

When jointing compound is used, apply in a thin
uniform film to metal surfaces; take care to
prevent jointing compound from entering
oilways, pipes or blind tapped holes.

If gaskets and/or jointing compound is
recommended for use; remove all traces of old
jointing material prior to reassembly. Do not use
a tool which will damage the joint faces and
smooth out any scratches or burrs using an oil
stone. Do not allow dirt or jointing material to
enter any tapped holes or enclosed parts.

Prior to reassembly, blow through any pipes,
channels or crevices with compressed air.

Locking Devices

General
Always replace locking devices with one of the same
design.

Tab washers
Always release locking tabs and fit new locking
washers. Do not re-use locking tabs.

Locking nuts
Always use a backing spanner when loosening or
tightening locking nuts, brake and fuel pipe unions.

Roll pins
Always fit new roll pins of an interference fit in the
hole.

Circlips
Always fit new circlips of the correct size for the
groove.

Keys and keyways
Remove burrs from edges of keyways with a fine file
and clean thoroughly before attempting to refit key.

Clean and inspect key closely; keys are suitable for
refitting only if indistinguishable from new, as any
indentation may indicate the onset of wear.

GENERAL INFORMATION

03-10

Split pins

Always fit new split-pins of the correct size for the
hole in the bolt or stud.

Screw Threads

General
Metric threads to ISO standards are used.

Damaged nuts, bolts and screws must always be
discarded. Cleaning damaged threads with a die or
tap impairs the strength and fit of the threads and is
not recommended.

Always ensure that replacement bolts are at least
equal in strength to those replaced. Castellated nuts
must not be loosened to accept a split-pin, except in
recommended cases when this forms part of an
adjustment.

Do not allow oil or grease to enter blind threaded
holes. The hydraulic action on screwing in the bolt or
stud could split the housing.

Always tighten a nut or bolt to the recommended
torque figure. Damaged or corroded threads can
affect the torque reading.

To check or re-tighten a bolt or screw to a specified
torque figure, first loosen a quarter of a turn, then
retighten to the correct torque figure.

Oil thread lightly before tightening to ensure a free
running thread, except in the case of threads treated
with sealant/lubricant, and self-locking nuts.

GENERAL INFORMATION

03-11

Bolt and Nut Identification

Bolt identification

An ISO metric bolt or screw made of steel and larger
than 6 mm in diameter can be identified by either of
the symbols ISO M or M embossed or indented on
top of the bolt head.

In addition to marks identifying the manufacturer, the
top of the bolt head is also marked with symbols
indicating the strength grade, e.g. 8.8; 10.9; 12.9;
14.9. As an alternative, some bolts and screws have
the M and strength grade symbol stamped on the
flats of the hexagon.

Encapsulated bolts and screws

Encapsulated bolts and screws have a micro-
encapsulated locking agent pre-applied to the
thread. They are identified by a coloured section
which extends 360

around the thread. The locking

agent is released and activated by the assembly
process and is then chemically cured to provide the
locking action.

Unless a specific repair procedure states otherwise,
encapsulated bolts may be re-used providing the
threads are undamaged and the following procedure
is adopted:

Remove loose adhesive from the bolt and
housing threads.

Ensure threads are clean and free of oil and
grease.

Apply an approved locking agent.

An encapsulated bolt may be replaced with a bolt of
equivalent specification provided it is treated with an
approved locking agent.

GENERAL INFORMATION

03-12

Self-locking bolts and screws

Self-locking bolts and screws, i.e. nylon patched or
trilobular thread can be re-used providing resistance
can be felt when the locking portion enters the female
thread.

Nylon patched bolts and screws have a locking agent
pre-applied to the threads. They are identified by the
presence of a coloured section of thread which
extends for up to 180

around the thread.

Trilobular bolts (i.e. Powerlok) have a special thread
form which creates a slight interference with the
thread of the hole or nut into which it is screwed.

DO NOT re-use self-locking fasteners in critical
locations (e.g. engine bearings, flywheel). Always
use the correct replacement self-locking nut, bolt or
screw.

DO NOT fit non self-locking fasteners in applications
where a self-locking nut, bolt or screw is specified.

Nut identification

A nut with an ISO metric thread is marked on one
face or on one of the flats of the hexagon with the
strength grade symbol 8, 12, or 14. Some nuts with a
strength grade 4, 5 or 6 are also marked and some
have the metric symbol M on the flat opposite the
strength grade marking.

A clock face system is sometimes used as an
alternative method of indicating the strength grade.
The external chamfers or a face of the nut is marked
in a position relative to the appropriate hour mark on
a clock face to indicate the strength grade.

A dot is used to locate the 12 o'clock position and a
dash to indicate the strength grade. If the grade is
above 12, two dots identify the 12 o'clock position.

When tightening a slotted or castellated nut, never
loosen it to insert a split pin except where
recommended as part of an adjustment. If difficulty is
experienced, alternative washers or nuts should be
selected, or the washer thickness reduced.

Where bearing pre-load is involved, nuts should be
tightened in accordance with special instructions.

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