[TowerTalk] Rotor Shims

[Stan Griffiths]

>If it's straight, I can only think to use the shims referenced in the CDE
>rotor manual.  What type of material is suitable as shim material?  My
>understanding of what I read in the manual is that the shimstock should be
>wrapped around the mast to keep the mast centered in the rotor clamp.  Will
>Aluminum sheet metal work?

Hi Gang,

It really is important to shim between the rotator and mast to make SURE the
center of rotation of the rotator and center of rotation of the mast are as
close to exactly the same as you can get it.  Not doing this is one of the
causes of the rotator bell housing bolts backing out over time and then
raining ball bearings.

You do not have to wrap shim stock all around the mast to put it in the
center of the rotator.  You only need to shim the two surfaces where the
mast contacts the casting part of the bellhousing.  Sheet aluminum (1/32
inch) works just fine and I make a couple of strips about an inch wide and
about 6 inches long (bent over for about 1/2 inch at the top so they hang on
the upper lip of the bellhousing). 
If I recall what I read in the rotator manuals, the rotators are made for
masts with an OD of 2 1/16 inch.  This means they need to be shimmed 1/32 on
the two surfaces where the mast contacts the bellhousing.  There is no need
to shim between the mast and the ubolts since that would only serve to move
the ubolts out from the mast and would have no effect on centering the mast
on the center of the rotator.

The order in which you tighten the various bolts holding it all together
makes a big difference, too.  I essentially install all the hardware "finger
tight" and then tighten in the following order:  FIRST:  Ubolts that attach
the rotator to the mast.  This assures the mast and rotator are parallel
which they MUST be to prevent binding.  SECOND:  The four bolts under the
rotator shelf that bolt the shelf to the rotator.  This assures that the
shelf is flat against the bottom of the rotator where it must be to prevent
binding.   THIRD:  Ubolts holding the shelf tight against the tower legs.
They will find their own correct position and that is where they should be
tightened even if the shelf is not resting flat on the tower horizontal bracing.

Almost everyone I know tightens the hardware in the OPPOSITE order I have
mentioned above and this often leads to the rotator and mast fighting with
each other and you either get binding or rotators that eventually unbolt
themselves on the tower.  Seen this MANY times.

Stan  w7ni@teleport.com


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