8999129: v1 11/09/2018
Page 6.3 of 6.5 pages
Original instructions (ENGLISH)
Website: www.spearheadmachinery.com
6.4.3
Shear bolt protection
(If fitted)
The P.T.O. shaft is fitted with a shear bolt overload
protection to prevent damage to the machine if an
obstacle is encountered during operation. The shear
bolt is located at the machine end of the PTO shaft. The
following procedure should be followed when replacing
or inspecting the shear bolt.
Figure 6.3
Disengage the PTO.
6.4.3.1
Raise the machine on the lift arms and move to an area with a firm, level surface.
6.4.3.2
Lower the machine and stop the tractor.
6.4.3.3
Apply the parking brake and remove the starter key.
6.4.3.4
Release the guard restraining chains and disconnect the PTO shaft from the tractor end first, and then
6.4.3.5
from the machine. This will give access to the shear bolt for inspection and replacement.
Inspect the machine, shaft and ground for possible causes of failure. Check that the blade rotates
6.4.3.6
freely and does not foul on the body.
Remove any bolt remains from the universal joint and replace the shear bolt with the correct grade of
6.4.3.7
new bolt. Four spare shear bolts and nuts are supplied with each new machine. These are stored on
the ‘A’ frame or the headstock gearbox mounting plate. Ensure the bolt is correctly tightened, see
Figure 6.3.
CAUTION: Only use the size and grade of shear bolt as supplied by Spearhead Machinery. For further
information refer to the Serial number specific parts book supplied with your machine.
Connect the shaft to the machine and then the tractor and attach the guard check chains.
6.4.3.8
Re-start the machine as described in
‘Running the Machine for the First Time’, see section 6.4.8, and
6.4.3.9
check that it operates correctly.
6.4.4
Setting slip clutch PTO
(Option - if fitted)
It is important that the clutches slip when an obstacle or load heavier than the clutch setting is encountered.
Therefore, if the machine sits outside longer that 30 days and is exposed to rain and/or humid air, it is important
to make sure that the clutch lining plates are not rusted/corroded together. Before using the machine, use the
following procedure to make sure the clutch will slip and give the overload protection required.
Measure the spring lengths. These should be
6.4.4.1
33.2mm on a 540rpm machine, and 33.0mm on
a 1000 rpm machine. Spring compression and
the clutch friction material determines the power
transferred through the clutch.
Loosen the nuts on all springs, see
6.4.4.2
Figure 6.4 A, just until the springs can freely
rotate, yet remain secure on bolts.
Mark the outer edge of the friction plates as
6.4.4.4
Figure 6.4 B.
Set the PTO speed to that detailed in Section
6.4.4.6
1.4 ‘Machine general specification’.
Start the tractor engine and engage the PTO
6.4.4.7
(for approximately one second duration) and
then quickly disengage it. The friction lining
plates should break loose.
Turn the tractor off, engage parking brake and
6.4.4.8
remove and pocket the key.
Figure 6.4
Inspect the previous marking on the friction plates. The mark should now be out of alignment, showing
6.4.4.9
that the slip clutches have operated. If not, completely dismantle and clean all mating surfaces.
If the above power test is successful and the marks are not aligned, then tighten the nuts on the
6.4.4.10
springs to their original position (see
Figure 6.4 C) and replace all guarding.
