[TowerTalk] Thrust Bearing Concerns

[kq2m at kq2m.com]

I second what Jim wrote.

On each of my towers I use two TB-3 Thrust Bearings and also a separate 
Rohn AS45 accessory shelf with a Muffler Clamp clamped tightly to the 
mast. This easily supports the weight of mast plus antennas while the 
rotator is being swapped out, or taken out to lower/raise the mast for 
antenna work.  It also has the added advantage of if/when the Thrust 
Bearing needs to be replaced or reconditioned or loosened for some other 
reason, the shelf plus galvanized muffler clamp can easily support the 
weight safely and you can actually tilt the mast within the top of the 
tower to allow greater access to replacing anything.

It gives many options to the climber while at the same time increasing 
safety and convenience at every step in the process.

It's relatively cheap insurance that protects the antenna and rotator 
installation as well as the people doing the work at the top.  If you 
use a second Rohn Accessory Shelf on a very long heavy mast, it is even 
easier and safer to do the work and you may not even need to loosen a 
Thrust bearing as most of the weight can be is resting on the shelf at 
all times.  Depending on your installation, you might not even need a 
Thrust Bearing at all!  The muffler clamp provides a convenient 
attachment point for a comealong tool to raise/lower the mast.

My TB-3's have lasted a lot longer since I have started using the 
accessory shelves and muffler clamps.

73


Bob, KQ2M


On 2025-06-22 11:57, jim.thom jim.thom at telus.net wrote:
> Put a clamp around the mast, so it's sitting on top of the  top thrust
> bearing.
> I would suggest using 2 x thrust bearings.  one at top of tower, and
> another 3-6' down the tower,  with the  PP  below that.
> 
> On my rohn  TB-4 thrust bearings (3" mast) the 3 x setscrews all rusted 
> out
> and seized up.  The ball bearings also started to grind, water got in
> there..and that was < 1 year.