[TowerTalk] Rohn Trust Bearing

Roger (K8RI) K8RI-on-TowerTalk at tm.net
Tue Dec 4 18:38:18 EST 2007

>I have a pair of Rohn thrust bearings in the top of my tower. The set 
> have rusted and the tower guy told me that he couldn't unscrew them. I am
> going to have to remove those set screws so that I can take the 20' mast 
> out

PB-Blaster (TM), or Mouse Milk (TM) - (both much more effective than WD-40) 
and patience.  Dose them up real good, give them a day and then try. If they 
don't budge, repeate (maybe several times). I've had to resort to this on 
several occasions but it has always worked (so far).  I've replaced most of 
the bolts in my TB-3s with SS and a dose of NeverSeize(TM). Actually I think 
a good dose of Moly Disulphide grease would also work.  Just remember with 
either it becomes much easier to put much more pressure on the shaft with 
the bolt than when dry. I also use a lock nut on each bolt.

> of the top of the tower. The mast is currently sitting on a HAMM rotator 
> and
> the bottom thrust bearing is about 12" above the rotator and about 5 feet
> down in the tower. The top thrust bearing is mounted on the top of the
> tower. (120 feet of Rohn 25)
> Since I don't seem to be able to unscrew those set screws, what are my
> options? I suppose I could have him drill them out. Probably need to 
> replace
> the thrust bearings anyway.

Unless overloaded the TB-3 should last a very long time.  OTOH with two of 
them on the same steel shaft only 5 feet apart differential expansion 
between the tower and mast might either put excessive pressure on/between 
them or reduce the load to a negative on one.

However it's been my experience the design of the TB-3 and 4 is not optimum 
for handeling side thrust and the Ham-M needs some weight on the bearings. 
I destroyed one TB-3 with the side thrust from the big array above the top 
of my tower. In my case I'd have been better off by having a bushing, or 
sleeve bearing made to take the side thrust and let the PST-61 support the 
load as It's capable of supporting much more than a TB-3 or 4. (It uses car 
wheel bearings top and bottom)

As a final trail if the BP-Blaster treatment fails I've used a device 
similar to an impact wrench. You fit it over the nut, and then give it q 
good whack with a hammer. Even though the hammer force is "in" the turn 
direction is "out". I have a *BIG* screwdriver made like this and it could 
be adapted to hold a socket. It's removed large screws that I had figured 
wre beyond hope.

Good Luck,

Roger (K8RI)
> Anybody had this problem?
> Bill, W5VX
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