[TowerTalk] MA550 Tubular Tower Binding.

Dick Green wc1m at msn.com
Sun Apr 15 13:33:31 EDT 2007


Ron,

I had binding problems with my MA-770MDP with the rotating base. The primary
culprit was the coupling between the rotor and the tower drive shaft. Having
no instructions, I tightened the nut on the bolt that connects the short
coupling pipe to the drive shaft. Unbeknownst to me, the coupler acts as a
poor-man's u-joint. The coupling has to be able to flex in order to
compensate for the fact that the tower can never be made perfectly plumb.
The bottom tube itself isn't perfect, and you will find that it sways ever
so slightly as it rotates. That's because there's no upper thrust bearing,
just a retaining ring.

There are a few other things to check as well. Here's what I suggest:

1. U.S. Tower informed me that the top ring must be lubricated for the tower
to rotate smoothly and avoid abrasion between the ring and tube. Crank the
tower down, connect the cable from the tilt fixture, open the top ring,
remove the small bolts from the thrust bearing and tilt the tower over until
it is clear of the ring. Smear a good layer of grease on the inner
circumference of the ring. You can use automotive grease, lithium grease, or
any grease that won't wash away easily in the rain. Also smear some grease
around the tube where it will contact the ring. Crank the tube back to the
vertical, close and bolt the ring and put the small bolts back in the thrust
bearing assembly. Disconnect the cable from the tilt fixture. Do not raise
the tower at this time. Note: you should periodically squirt some grease in
the gaps between the ring and tube if it looks like the grease is wearing
off.

2. While you have the grease out, lubricate the thrust bearing. It has a
grease nipple in the front (the direction the tower tilts) for this purpose.
You need a grease gun with a female fitting to do this. They're available at
any automotive supply. Pump grease into the bearing until you just see it
begin to squirt up between the mounting and bearing race. Get a male grease
fitting, too. You can use it to squirt grease in the ring gaps, per #1
above.

3. Plumb the tower. Adjust the base mounting bolts so that the *bottom tube*
is plumb all the way around its circumference. Use a 4-foot carpenter's
level if you can. *Do not* attempt to plumb the base vertical member! It may
not be perfectly parallel to the bottom tube. It's the tube that must be
plumb, not the base member.

4. Remove the rotor and lower the rotor mounting plate.

5. At this point, the tower should rotate easily and smoothly all the way
around when you turn it by hand. When properly leveled and greased, even my
1200-lb MA-770MDP with a big antenna mounted can be turned easily by
grasping the bottom tube and turning it. Without an antenna mounted, I can
even grasp the small drive shaft at the bottom and turn the tower all the
way around. If your tower still binds with the rotor removed, there's a
mechanical defect. It could be a bad thrust bearing, in which case the
bearing probably will have to be replaced. Another possibility might be a
bent drive shaft, perhaps the result of shipping damage. If that's the case,
you'll have to contact U.S. Tower for advice. Another, less likely,
possibility would be a manufacturing defect in the top ring or bottom mount.
My tower base was not built exactly according to specifications -- clearance
between the bottom mount and base was a couple of inches less than spec,
forcing me to cut off the tops of the base mounting bolts to get enough
clearance for my rotor! 

6. If the tower rotates freely with the rotor removed, then you're in good
shape. You just have to make sure the coupler is set correctly and the rotor
is properly aligned with the drive shaft. Loosen the nut on the bolt
connecting the coupling pipe to the drive shaft enough so that the pipe can
swing back and forth freely. It's an aircraft nut, so it won't come off.
It's been many years since I set mine, so I don't recall if I left any
clearance between the nut and pipe. I think I left very little, but you can
play around with that. I believe the main object of the game is for the pipe
to swing around the bolt, not slide back and forth on it.

7. Clamp the coupling pipe in the rotor jaws. This will leave the rotor
dangling from the pipe, and it should align itself with the drive shaft.

8. At this point, we need to talk about the rotor mounting plate. If you're
like me, you were a bit perplexed about how to mount the plate to the base.
It can be mounted with the vertical plate pointing up or down -- the plate
as viewed from the side being either L-shaped or inverted-L-shaped. It turns
out the vertical and horizontal portions of the plate are not exactly
perpendicular, so it makes a difference which way the plate is oriented.
U.S. Tower uses a jig to weld the two plates, so this is deliberate. I
believe that the reason for this is that the base vertical member isn't
exactly parallel to the tube, as mentioned above. It leans slightly away
from the tower. Anyway, the plate is supposd to be mounted so that it's
L-shaped when viewed from the side -- vertical plate pointing up. I
originally mounted mine the other way because there wasn't enough clearance
between the plate and base bolts to mount my rotor. As mentioned above, that
was due to a manufacturing defect. The point is that if you mount the plate
upside down, it won't be perpendicular to the tube mounting and the tower
may bind.

9. Assuming you have it mounted correctly, raise the rotor mounting plate
flush against the rotor base. Make sure the plate is level and flat against
the base of the rotor before you tighten the bolts that hold it to the base.
Insert the rotor mounting bolts and gradually tighten in a cross pattern,
like you would with a cylinder head. You may have to play around with this
to get the alignment right. It might be better to tighten the rotor mounting
bolts before the plate mounting bolts. However, the coupling pipe ensures
that the alignment doesn't have to be perfect.

10. At this point, the rotor should turn the tower through the entire
rotation without binding. If it does, raise the tower and make sure that's
still the case (I assume you have an antenna mounted.)

11. If the tower binds only when extended, then the load at the top may not
be properly balanced and is throwing the bottom tube too far out of plumb to
rotate freely. You can either try to adjust the antenna boom mounting point
a little at a time, or remove the antenna and find the balance point.

Hope this helps. Feel free to contact me if you need more help. I have
pictures of my tower showing the rotor mounting if you need a visual. Do let
us know the results.

73, Dick WC1M



> -----Original Message-----
> From: Ron [mailto:kk7go at razzolink.com]
> Sent: Saturday, April 14, 2007 12:24 PM
> To: towertalk at contesting.com
> Subject: [TowerTalk] MA550 Tubular Tower Binding.
> 
> Hello All,
> 
> I have installed a US Towers MA-550 Tubular tower with the free
> standing rotor base. I made sure the tower is plum. Connecting the
> rotor assembly has gone well.
> 
> After all of that, the tower experiences binding. I have rechecked the
> tower for being plum and that the rotor is lined up as best as I can.
> The tower will swing 270 +/- and then stop. I can go the other way
> without any stoppage.
> 
> After a closer look at the thrust bearing, I think I see that the tower
> race may not be sitting flush on top of the bear. I do not know what
> the ring at the base of the tower that has a allen set screw is for and
> I have not messed with it.
> 
> Any ideas to fix this problem without taking down the antenna? (It is a
> Force-12 C-4)
> 
> I think I know the answer to this, but I am looking for any information
> that might help.
> 
> Thanks,
> 
> 73
> 
> Ron
> KK7GO



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