8
General Information
Safety instructions for
fluororubber
Fluororubber is a common material used in sealing
rings for shafts and O-rings.
Hydrofluoric acid is formed when fluororubber is
exposed to high temperatures (over 300°C/572°F),
and is strongly corrosive. Contact with the skin, eyes,
or respiratory passages, can lead to severe injury.
WARNING! Observe extreme caution when
working on engines that may have been ex-
posed to high temperatures, e.g. overheating
during seizing or fire. Seals must never be
burned off during dismantling, or burned up in
uncontrolled circumstances.
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Always use chloroprene gloves (for handling
chemicals) and protective glasses.
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Handle the removed seal in the same way a cor-
rosive acid. All residue, including ash, can be
strongly corrosive. Never use compressed air to
blow clean.
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Place the remains in a sealed plastic container
with warning label. Wash gloves under running
water before taking off.
The following seals are in all probability manufac-
tured of fluororubber.
Sealing rings for crankshaft, camshaft, and interme-
diate shafts.
O-rings, irrespective of position. O-rings for cylinder
lining seals are almost always made of fluororubber.
Note that seals that have not been exposed to
high temperatures can be handled normally.
Angular torque
For angular tightening the screw union is first tight-
ened with a given torque, after which tightening con-
tinues at a predetermined angle. Example: for 90°
angular torque the union is tightened an addition ¼
turn after the given tightening torque has been
achieved.
Lock nuts
Dismantled lock nuts should not be reused but re-
placed with new ones, since the locking properties
become inferior or non existent after multiple use.
For lock nuts with plastic inserts, e.g. Nylock
®
, the
tightening torque indicated in the table should be re-
duced if the Nylock
®
nut has the same nut height as
a standard solid metal hex nut. The tightening torque
is reduced by 25 % for screw sizes of 8 mm or more.
For Nylock
®
nuts with higher nut size, where the sol-
id metal thread is the same height as a standard hex
nut, the tightening torque as per the table is applica-
ble.
Strength classes
Screws and nuts are divided into different strength
classes. Their classification is indicated on the screw
head. A high number on the marking represents a
stronger material, e.g. a screw marked 10-9 is
stronger than a screw marked 8-8. It is therefore im-
portant when a screw union is dismantled to return
the screws to their original positions. See the spare
parts catalogue when replacing screws to ensure
that the correct version is used.
Size
Tightening torque, Nm (lb.ft)
M5 ......................................................
6
(4.4)
M6 ......................................................
10
(7.4)
M8 ......................................................
25
(18.4)
M10 ....................................................
50
(36.9)
M12 ....................................................
80
(59.0)
M14 .................................................... 140 (103.3)
