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A4 - Interceptor
400 - How
do you change the mainshaft ?
seems to daunt new helicopter pilots, but in reality it is quite an
First of all,
disconnect the three connecting rods that go from the servos to the
swash plate at the swash plate end.
the anti rotation at the rear of the mainshaft backwards and tilt
the swash plate so that you can pull the locating pin out of the
Anti Rotation bracket by twisting it sideways a little,
Now look below
the main gear(s) you will see a 2mm metric screw or possibly a 2m
Cap bolt that goes through the base of the lower gear (the
autoration gear) and has a nut on the other side that locks the bolt
in place. Undo this bolt, taking care not to loose the nut.
Now you can
hold the very top of the mainshaft/head and gently pull upwards.
The entire mainshaft complete with the rotor head will slide up out
of the main gears and three main bearings, leaving the main gears in
If you are not
changing the main gear, leave it in place in the frame. If you
do slide it out, be careful to find and keep the small thrust washer
that sits on top of the main gear immediately under the lower main
bearing. This has a chamfered inner edge on one side that goes
DOWNWARDS when refitting the main gear.
entire head is on the bench, look at the bottom of the main CNC Mast
top casting, underneath the mixer arms etc, but above the washout
arms. You will find another 2mm screw or possible Cap bolt
with a nut on the other side. This is often called the
"Jesus Bolt" (for obvious reasons if it came out in
flight....) Remove this and keep the nut safely.
You can now
slide the entire head, mixer hub slider and swash plate off the top
of the mainshaft in one piece.
Get the new
Mainshaft, and measure from the centre of the machined groove to
each end. The LONGER END MUST GO DOWNWARDS in to the main
silver CNC locking collar that is left on the old main shaft, noting
which direction it is fitted, and put it on the new mainshaft the
same way up. Just LIGHTLY locate it in the groove on the new
mainshaft using the grub screw. Now slide the head back on,
swash plate first, then washout hub and finally the CNC Mast head
casting. Line up the hole in the top of the mainshaft with the
hole in the CNC Mast top, and refit the 2mm bolt and nut. Do
these up as tightly as you reasonably can.
the new main shaft and head assembly back down through the bearings
and wriggle the main gear until the mainshaft goes down through that
as well. Line up the hole in the mainshaft with the hole in the
autorotation gear, and fit the bolt and nut again.
that you do not twist the autorotation gear while doing this or the
metal centre CAN ROTATE in it, making the holes out of alignment for
the lower bolt. If this does happen to you, keep rotating it against
the pressure until you see the holes line up again.
final task is to adjust the locking collar by loosening the grub
screw, and then pulling the entire main shaft up firmly as far as it
will go, and relocking the collar so that it holds the mainshaft in
reposition the anti rotation pin on the swash plate through the slot
in the anti rotation bracket by bending the bracket backwards gently
reconnect the 3 connecting rods from the servos to the swash plate.
ALL THERE IS TO IT...
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