This was some input to a debate on Tower Talk about using two thrust bearing. I could not find any additional thrust bearings on the used market, so here was what I came up with to solve the problem.
As the debate goes on.... I really don't have any creditable input for the debate, but had decided several months ago to design a holding fixture that would fit inside a Rohn 45 tower some where between the rotator and the thrust bearing.
Wanted it to provide for two purposes.
1. to hold the mast/antennas when changing the rotor.
2. include two attachment points for pulley(s) at the bottom of the fixture. So that a clamp could be fastened temporarily to the mast near the top of the rotator and the mast and antenna(s) could be raised to a distance to permit the rotator to be removed.
Depending on pulleys, this would provide a 4 to 1 or 8 to 1 mechanical advantage. I am going to have a 40-2CD, 204BA and a chrome moly 2" x 1/4" x 21' mast--approximately 250+ lbs.
Based on the initial design and the machine shop input here is what we can up with. This will fit into a R45 section and fasten on the sides with U-clamps. Needs some paint, but here are some pics of the finished fixture...
Additionally, I thought that if I had to remove the rotator for repair and if it was going to be an extended period, that I would place a steel plate in place of the rotator and allow the mast and antennas to rest on the plate and not on the holding bolts in the fixture or the thrust bearing.
It was totally manufactured from scrap (BTW there is no such thing in a welding shop.. hi)... He made this and a couple for accessory plates for the rotator and thrust bearing to fix a r45 section and aligned the center holes.
For what it is worth...