ICFR – Chainsaw Safety and Operating Handbook
43
A new chain drive sprocket should be installed with
each new chain. However, as a chain drive sprocket
normally has a wear life equivalent to two chains, it
is advisable to use two chains in rotation with one
sprocket. In this way the sprocket and chain bed-in
with each other and wear out together. If a new chain
is installed on a half-worn sprocket, its drive links will
wear very quickly.
The following rule of thumb is a good guide for the
economic operation of a chainsaw:
•
Use 1 guide bar, 2 chain drive sprockets and 4
chains in rotation.
14.1.6
c
hAin
tenSion
A slack or loose saw chain is the cause of most chain
problems. Loose chains can:
•
Climb up on the sprocket.
•
Damage the guide bar rails.
•
Cause wear to cutters, tie straps and the guide bar.
•
Cause the chain to de-rail off the guide bar.
Correct tension, break-in and lubrication of the
saw chain are individually and collectively of great
importance to the service life of the cutting attachment.
They also have a major effect on the wear of engine
components.
Chain tension adjustment procedure:
•
Never adjust the chain tension with the engine
running.
•
The cold tensioned chain should fit snugly against
the underside of the guide bar so that it can still
be pulled along the guide bar by hand.
•
As there is much less friction on the sprocket nose
type of bar, the chain can be tensioned more than
on solid nose bars.
•
Press the bar upwards or support it firmly from
below when the bar nuts are tightened. This will
prevent the bar from altering its position once
cutting has started and ensure that the correct
tension is maintained.
•
Extreme care should be taken when checking chain
tension as the cutting edges are sharp and could
cause cuts. Wear both gloves when handling chain.
•
During cutting, the chain warms up as a result of
friction, and expands. This causes the chain to
slacken and eventually sag on the underside of
the bar, requiring the chain to be retensioned.
•
Chain tension should be checked at frequent
intervals in normal working conditions.
14.1.7
r
unning
-
in
the
SAw
chAin
The chain should be submerged in chain lubricant
overnight before use. The chain requires a certain initial
period after start-up for the individual components to
bed in. This period is known as break-in or running-
in. The break-in time for new chain is about 3 minutes
with the engine running off load (without cutting).
As the frictional stress during break-in is particularly
high it is essential to ensure adequate lubrication. On
machines with a lubrication flow control, the control
should be set to maximum flow. During running-in
a few light cuts should be made as this facilitates
the bedding in of the individual components. The
chain will still stretch a little and therefore it must be
retensioned during the process.
14.1.8
c
hAin
lubricAtion
Apart from chain tension and regular care and
maintenance, lubrication is the factor that has the
greatest influence on the life of the cutting attachment.
Friction is generated between the sliding faces of the
chain links and bar, and also in the chain joints, as the
tensioned chain travels over the guide bar. If the bar
rails and chain are dry it results in frictional heat which
quickly increases the temperature of the chain and bar
and finally causes them to wear at an accelerated rate.
It is therefore necessary to introduce a chain lubricant
film between the sliding surfaces and joints to reduce
friction.
Owing to the centrifugal force that occurs as the chain
rotates around the bar, a certain amount of chain lubricant
is thrown off the cutting attachment. In addition, some
lubricant is wiped off the chain in the cut and some is
absorbed by the chips. It is therefore necessary to provide
an ample and continuous flow of lubrication to the bar and
chain whilst the chain is running.
The lubrication pump supplies the necessary quantity
of lubricant to the bar mounting flange and from there
through the inlet hole to the guide bar groove. The
drive link tangs distribute the lubricant over the length
of the guide bar.