[TowerTalk] Rohn TB3 or TB4

[K7LXC at aol.com]

In a message dated 1/11/2007 2:19:46 P.M. Pacific Standard Time,  
towertalk-request at contesting.com writes:

>> Steve, K7LXC at aol.com, Wrote:

>> I found this on  ebay. It's a Rohn thrust  bearing and it says that it's 
been
"FRESHLY  PACKED WITH WHITE LITHIUM  GREASE". Gentlemen, these bearings are  
NOT
supposed to be lubricated. Do not buy  this unless you unpack  the grease.
Don't be a loser like this guy.

>  So you're all  saying that lubrication should not be used with a Rohn 
thrust 
bearing  ?


    Yessireebob. It's designed to be unlubricated.  

>  I just took down a tower that had not been used for quite a  few years. It 
had a Triband beam and a TB3. I thought I had hit the  jackpot.

>  Until I tried to turn the bearing. It was locked up  !

>  I disassembled everything and took it alll home. When I  got the bearing 
into 
the shop, I put it in the vise and tried to turn it.  Still couldn't turn it. 
So I removed the allen screw and removed the  bearings so I could take the 
races apart.

>  The balls, by  the way, were not shiny. They had a matte finish. Once I 
got 
the races  apart, I could see why it would not turn.

>  First, the races  are aluminum.  Poor (No, BAD) engineering practice, IMO. 
The balls,  sitting in one place for years, wore into the aluminum race and 
the AlO2  that had developed over the years, ground into the races. It also 
ground  into the steel balls, giving them their matte finish.

>  The  outer race which is the main flange that bolts to the tower plate, 
was  
worn into a multiple scallop shape. The balls sat in those scallops and  
would not turn.



Howdy, 
 
    Yes. That's what happens when it sits in one  spot. The wind force causes 
the steel bearings to hammer into the softer  races.

>  I don't know if lubrication would have made any  difference in this case, 
since the rotor had not turned for so  long.


    It wouldn't have because the races would still  have gotten hammered. 

>  I would imagine that if the race had  been filled completely (like we used 
to 
do with wheel bearings - the  roller bearings that we squeeeezed the grease 
into) that dirt would not  have gotten in.
 
    Au contraire. Actually the grease attracts dirt,  girt, pollution 
particulates, etc. so it would actually accelerate the wear  with all that junk in 
it. The problem you described was due to it being in the  same spot for a long 
time. 

>  For the time being, I have built  back the bad races with TIG and am going 
to 
remachine the grooves and use  new balls and see if I can reuse the bearing. 
If not, I'll put up a STEEL  bearing.


Like what? The machine shop type pillow blocks  are not suited for outdoor 
use and they only use a single small Allen screw to  pin the mast.

>  I really think the loser is the Rohn engineers who  produced the TB2, TB3 
and 
TB4.


Well, anything that sits outside for a long  period of time is going to have 
problems. It's an okay design that does have  its limitations. 

>  Makes me really wonder why Rohn went  bankrupt....
 

They were a victim of over-expansion  during the big telecommunications 
build-out in the 90's and got  caught being overextended when everyone stopped 
building tower sites. 
 
Cheers,
Steve      K7LXC
TOWER TECH -
Professional tower services for hams
Cell: 206-890-4188