GRAUPNER heim UNI-Mechanik 2000 Mode D'emploi page 58

1.5 Assembling the main gearbox
Fit the main rotor shaft bearing holder and the dome bearing holder between the mechanics
side frames 4450.9 and 4450.10, and secure them using M3 x 16 socket-head cap screws as
shown. Temporarily fit the main rotor shaft 4448.43 through both bearings, so that you can
install the previously prepared spur gear and freewheel at the bottom, and engage it with the
pinion on the layshaft, which is already installed.
Now check and adjust the meshing clearance of the spur gear and pinion. This is important, as
this setting defines the maximum load capacity, durability and longevity of the mechanical
system. It is very important to make this adjustment as carefully and as accurately as you can.
The first step is to set up the gears without any play at all (i.e. the gears hard up against each
other). The meshing clearance between the spur gear and the layshaft pinion can then be
adjusted by loosening the M3 x 16 socket-head cap screws slightly in the bearing holders,
winding a piece of thick writing paper in between them, and finally re-tightening the screws.
Note: the correct meshing of these two gears depends on several factors, and one of them is
manufacturing tolerances in the bearing holders; i.e. a possible non-central location of the brass
inserts to which the side frames are attached.
If there is substantial meshing clearance evident when you first assemble the system, then your
first step should be to remove the bottom main rotor shaft bearing holder, rotate it horizontally
through 180º and install it again.
• If the gears are now hard up against each other, you can adjust the play as described above.
• If the meshing clearance is reduced when you do this, but does not disappear completely,
then you also need to rotate the bottom layshaft bearing holder through 180º and re-install it.
This second change must eliminate any play, and you can now make the adjustment as
described above.
• If the amount of play is increased when you do this, then you should reverse the procedure,
and install the bearing holder in its original position. In this case rotating the bottom bearing
holder eliminates the play in the layshaft, which can then be adjusted as described above.
Fit the tail rotor drive unit (prepared in Stage 1.1) between the side frames and secure it using
UNI-Mechanics 2000
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