[TowerTalk] FWD: Refurb Your Rohn TB-3 Thrust Bearing

[Jim Idelson]

I hope this is now easier to view on your browser . . .

Refurbishing Your Rohn TB-3 Thrust Bearing
Jim Idelson, K1IR

In the last two weeks, I've refurbished two Rohn TB-3 thrust bearings. One was running very rough.
The other was "sticking" at several points in its rotation. After refurbishing, they both run very smoothly.
This procedure is only intended to help improve the operation of a reasonably "healthy" unit. If you find
serious problems, like cracked castings, broken or missing ball bearings, extreme wear, or cross-threaded
screws - please do the wise thing and replace it with a brand new thrust bearing.

Thanks to Fred, K1VR for providing the thrust bearings to rework, and the reminder that I should post
this information for the benefit of all. 

Here's what you'll need:
1.	A clear, well-ventilated, well-lighted workspace
2.	A 16" x 24" or larger tin baking sheet with edges [so you don't lose the ball bearings]
3.	A rag for cleaning
4.	Mineral spirits for cleaning
5.	3/16" Allen key [preferably with a 6" handle and "rounded" end for insertion at an angle]
6.	Miscellaneous filing tools [i.e. small hand files - round, flat; a Dremel tool with fine grinding capability]
7.	Wrenches

Procedure:
1.	Remove all the bolts and nuts that secure the bearing to the tower and the mast into the bearing.
2.	OVER THE BAKING TIN, CAREFULLY remove the Allen set screw located on the inside wall [where
the mast goes through].
3.	The ball bearings will begin to fall out of the set screw hole. Rotate and lightly shake the bearing to
coax the ball bearings out of the hole.
4.	The unit was built with 32 [THIRTY TWO] ball bearings. Make sure you have them all! Set them aside.
5.	Separate the top and bottom castings of the bearing.
6.	Clean both castings and all the ball bearings with the rag and the mineral spirits or other grease-cutting
cleanser.
	Note:  It is normal for some dirt and metal powder to accumulate. The bearing should not contain grease.
This unit is designed to run dry.
7.	Inspect the ball bearing races. Look for unusually worn areas, pitting, cracks. Try rolling a ball bearing in
suspect areas to see if it will get "hung".
8.	Using your filing tools, smooth out any rough areas so the ball bearing can roll without resistance.
9.	Do this for both castings. Note that your mast will be pushing down on the upper casting. This will
cause the bearings to press against the top of the race in the upper casting, and against the bottom of the race
in the lower casting. Pay close attention to these areas.
10.	Make sure you look carefully at the area of the race in the upper casting near the set screw. I found that
wear in this area was causing one of the thrust bearings to stick.
11.	Insert the set screw - don't cross-thread it! Adjust it to the point where a ball bearing can run across it
smoothly. Note, from the insertion side, how far the set screw is screwed in. Remove the screw and set it aside.
12.	Reassemble the thrust bearing by holding the castings together and inserting the ball bearings back into
the set screw hole one at a time. You'll have to rotate and jiggle the unit to find space for the last 5 or 6 ball
bearings. Do this over your baking tin so that WHEN [not IF] you drop a ball bearing, it falls in the tin, not in the air
conditioning vent.
13.	Replace the set screw. Insert it until it is at the point you noted in Step 11. It should be roughly flush with
the inside wall of the upper casting. Be careful not to cross thread the set screw.
14.	Now it's time to give the bearing a spin. It should run much smoother, and should not "stick" at all.
15.	If you think the bearing could operate a little smoother, try adjusting the set screw in or out a bit. Remember,
the ball bearings must go by the set screw smoothly.
16.	If the unit still sticks . . . return to Step 2. If this is your second time through the process and you're still not
satisfied - THROW IT AWAY and go shopping for a new one.

73,

Jim K1IR

-------------------------------------------------------
The Information Resource for Conferencing Professionals
-------------------------------------------------------
James S. Idelson
President
DesigNET International, Inc.
96 Morse Road
Sudbury, Massachusetts USA 01776

tel	978.443.5549
fax	978.443.2034
pager	800.362.0156
email	jimi@designet.com
web	http://www.designet.com

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm