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Interceptor 400 answers



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A4 - Interceptor 400 - How do I change the main gear ?

This always seems to daunt new helicopter pilots, but in reality it is quite an easy job.

First of all, disconnect the three connecting rods that go from the servos to the swash plate at the swash plate end.

Carefully pull 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 autorotation 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 place.

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.

Once the 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 late 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 gear.

Remove the 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. 

Finally, slide 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.

Be careful 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.

The almost 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 that position.

Finally, 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.



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