Swinging Arm Bolt Advice

OK today I thought lets tackle the bolt and see what happens, un-did the left nut 30mm I think, and turned the right side 19mm I think and it moved.
Placed a small block of wood under the rear wheel to carry the weight of the rear suspension and knocked the pin all the way out with a 1/2 long extension, came out pretty easy. Once out it had a white oxidised material in the middle section which I would guess is from the engine ?. Cleaned it all up and greased it all over and slid it back in with my hand...slight tap to finish her off then torqued the main nut up to 80 foot pounds....job done.

Now my question is, what does the castle nut assembly on the right side actually do ?, I didn't remove this just the main pin. I have read the book about the pre-load it applies from the frame to the bearings does it just act as a spacer to stop the whole frame squashing up when you tighten the main pin ?, if yes then that explains what it does, why would you ever need to remove this ?, would I only touch this if I was removing the swinging arm / bearings etc ?.

Any simple mans explanation is welcomed

This is how I understand it.
The castle nut tightens the spindle onto the bearings and is torqued up first.
This is then locked by the standard type nut to a much greater torque.
The reason for this there is no give in the alloy frame as compared to a steel frame and that the frame would crack rather than bend to take up any play.
See this link
http://www.xr650r.us/preload/

Hew wrote:This is how I understand it.
The castle nut tightens the spindle onto the bearings and is torqued up first.
This is then locked by the standard type nut to a much greater torque.
The reason for this there is no give in the alloy frame as compared to a steel frame and that the frame would crack rather than bend to take up any play.
See this link
http://www.xr650r.us/preload/

Thanks for the reply I had read that link before but doesn't really make sense about how it works.
The castle nut doesn't tighten the spindle onto the bearings...the spindle comes out looking exactly the same as any other spindle...a long bolt with the bearing surfaces at either end and a single nut at theleft side torqued up to the 80 pounds etc.
I wondered if the castle nut arrangement stop the long bolt from crushing the frame together but why isn't there 1 on both sides ?, as I tighten the left nut it would surely squeeze the left side inwards ?.
All very confusing

On a steel framed bike as you tighten the nut on the spindle up it compresses the frame slightly against the bearings.
The designer felt that this frame would not compress and so the castle bush tightens against the bearings and the spindle nut tightens on the castle bush.
If you do not torque up the castle bush against the bearings but tighten the spindle nut onto the castle bush you could
have play in the swinging arm.
All you have done is take the spindle out so the castle bush may not have moved as you undid or fastened the spindle so it may be OK but it is an unknown.
When I removed the swinging arm to grease the bearings I had to undo the castle bush slightly to give clearance.
I torqued the castle nut up when i assembled it then torqued the spindle nut. The castle bush did not move as I tightened the spindle.

The side without the castle bush is the datum and the castle bush will tighten the bearings up against that.

Hew wrote:On a steel framed bike as you tighten the nut on the spindle up it compresses the frame slightly against the bearings.
The designer felt that this frame would not compress and so the castle bush tightens against the bearings and the spindle nut tightens on the castle bush.
If you do not torque up the castle bush against the bearings but tighten the spindle nut onto the castle bush you could
have play in the swinging arm.
All you have done is take the spindle out so the castle bush may not have moved as you undid or fastened the spindle so it may be OK but it is an unknown.
When I removed the swinging arm to grease the bearings I had to undo the castle bush slightly to give clearance.
I torqued the castle nut up when i assembled it then torqued the spindle nut. The castle bush did not move as I tightened the spindle.

The side without the castle bush is the datum and the castle bush will tighten the bearings up against that.

So am I right in thinking the left side outer frame is the fixed side then there is the swinging arm with it's clearances with the bearings fitted within it, then the right side frame. To enable the swinging arm to be fitted you need clearance, this clearance is removed my tightening the castle nut against the swinging arm which removes all the free clearance, hence this only needs a slight amount of load as all you are doing is removing the gaps, once nipped up the outer castle nut holds it in position then the spindle can be tighened up without fear of bending the frame inwards ?.
That would make perfect sense to me and expalin how the set-up is designed.
Thanks for the input.