I have never been impressed with Rohn thrust bearings. The first one that I
purchased didn't even turn and I had to return it to Texas Towers. I used
the replacement at my P40A station but it started getting tight so I
switched to a Create bearing which held up fine. Granted corrosion was
brutal in Aruba.. At my North Carolina station I used Luso thrust bearings
on my Rohn 65 and Rohn 55 tower. These bearings use six 12mm bolts to
secure up to a Ø4 1/2" (if I recall correctly) mast and they are very
heavy-duty. I had no issues with these Luso bearing or my prop pitch
rotators. I am not sure how much mast weight I had on my prop pitch
rotators when I installed them. It is unfortunate that you experience so
many prop pitch issues, and I know that you're not alone with this issue. I
hope that the water diversion works for you. I seems like a good idea, if
you have the McMaster-Carr part number it might be helpful. It appears that
there is no longer a source to get prop pitch rotators repaired which is
very unfortunate. They make a great antenna rotator.
John KK9A
Paul W9AC wrote:
I have a graveyard of 7-8 prop pitch rotators, all awaiting rebuilds one
day. In each case, failure resulted from water ingress, not mechanical
stress. As an experiment, a new method was tried: a silicone rubber sheet,
folded into a cone to form a shroud, was formed around the rotator. The top
of the cone is sealed around a 3-inch dia. Chromoly mast with stainless
Aeroseal hose clamps. At least now, the rotator is shielded against rain
and heating from direct sunlight exposure. The silicone sheet was ordered
from Master-Carr. It's the same torch-proof material that's used for tube
exhaust chimneys in many desktop RF amplifiers.
Regarding the weight distribution dilemma between a prop pitch rotator and
thrust bearing, I've never found a satisfactory answer based on facts. The
prop pitch supports a full-size 4 el 40m OWA at 140 ft and a 9 el 6m Yagi at
155 ft, both of which have 50 ft. booms.
A DXE TB400 thrust bearing recently replaced a similar Rohn type. The Rohn
bearing disintegrated into several pieces after just a few years. I've no
idea as to Rohn's thrust bearing composition, but it feels like "pot metal."
Paul, W9AC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|