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[TowerTalk] Refurb Your Rohn TB-3 Thrust Bearing

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Subject: [TowerTalk] Refurb Your Rohn TB-3 Thrust Bearing
From: (Jim Idelson)
Date: Wed, 9 Dec 1998 10:18:51 -0400
FROM:    Jim Idelson <>
TO:      YCCC <>
DATE:    Wed, 9 Dec 1998 10:13:10 -0400

RE:      Refurb Your Rohn TB-3 Thrust Bearing

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

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 
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.


Jim K1IR

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