Hi all,
Sorry to belabor the point on lubing Rohn TB-3 thrust bearings, but here is
another past article on re-furbishing the bearings. If nothing else, it's good
a good refresher course.
73
K9WN Jake
FROM: Jim Idelson <jimi@designet.com>
TO: YCCC <yccc@yccc.org>
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
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
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