Sounds like a good argument for a second thrust bearing to keep the mast
straight.
By coincidence, I just installed a 2-el Cal AV 40 (a rare beast) and an M2
OR2800PX. I bought and installed the wired bolt kit, and used medium Loctite
as well. The bolt wiring diagram made sense, but up on the tower I wasn't
able to figure out how to string the wires so that all four bolts would
tighten the wire if they attempted to loosen. One bolt was always in the
opposite state. Still, I think the wires will be more effective than
nothing, and maybe one of these days when I have nothing else to do I'll go
up there and see if I can figure out a better wiring path.
The biggest problem I ran into was registration of the rotor bolt holes with
the rotor plate. I didn't have a problem with the Tailtwister previously
mounted on the plate, but I was unable to get the rotor and plate holes to
line up perfectly. I kept ending up with one set of holes very slighly off,
such that the bolt would begin to slant as it went in (or, perhaps the hole
in the rotor casing was drilled at a slight angle -- I couldn't tell at the
time. I ended up slipping a couple of lockwashers over the bolt shaft so I
could tighten the bolt against the plate while it was still heading straight
into the casing. Seemed to work, but if that one loosens up it'll have less
travel to come out. However, the fit through the rotor plate of all four
bolts is so tight that I'd be surprised if they loosened up. Nonetheless,
this will be an annual maintenance check item.
73, Dick WC1M
> -----Original Message-----
> From: Barry Merrill [mailto:barry@mxg.com]
> Sent: Friday, June 06, 2008 1:24 PM
> To: 'Towertalk'
> Cc: jeremy@m2inc.com; n5ya@n5ya.com
> Subject: [TowerTalk] Hindsight: Check your rotator bolts
>
> In 2003, I (actually, I watched, while Bill, N5YA,
> and a 60 ton crane with 161 foot boom did the work)
> installed a US Tower HDBX72 with a 24 foot mast,
> and mounted a 2-el Cal AV 40 at the bottom and an
> OB16-3 at the top, turned with an Orion RC2800
> rotator, and have had zero problems and fantastic
> results.
>
> Yesterday, after a day of 50mph winds, I noticed
> that the antennas were rotated about 45 degrees,
> and then discovered I could not rotate them.
>
> After Reading The Fine Manual and making the voltage
> and resistance checks, which confirmed the motor
> was fine, I called M2 support and received excellent
> support, as Jeremy went thru the system and gave me
> additional diagnostics, in particular, to connect an
> ohmmeter to the counter wires, toggle the rotator
> control, and see if reed switch opened and closed,
> which it did, confirming the rotator electrics
> were not the problem.
>
> Looking at the rotator from the shack (from the West)
> I had seen nothing obvious, but when I then looked from
> the North, I could now see that the rotator was no longer
> in the center of the tower; the rotator was now flush
> with the West side of the tower, and the mast was 2-3
> inches off vertical at its bottom!!!
>
> Clearly, the bolts holding the rotator to the
> tower plate had loosened.
>
> When I called Jeremy back to thank him for the
> excellent diagnostics that eliminated elecrics
> and to report what I had observed, he said that
> this did, very rarely, happen, and that M2 now
> offered a set of bolts that were pre-drilled for,
> and were shipped with, safety wire, and he personally
> packaged a set (only he and the Purchasing manager
> were in the office, so he did it all!) and sent
> them via UPS early AM delivery (promised for 8:30am,
> the doorbell rang at 7:31am)!
>
> On the tower this morning, with the new bolts in hand,
> before the wind kicked up again, Bill discovered
> that two bolts were gone, one was still in place,
> but loose, and one had enlarged its hole in the
> tower plate so that it was above and sitting on
> the plate, cocking the rotator. Fortunatly,
> with ropes on the boom for horizontal pull,
> a jimmy bar in Bill's hand to lift, and a
> comealong strap around the rotator body,
> he was able to realign the rotator and its
> holes, and the new bolts AND SAFETY WIREs were in
> place with only about 2 hours tower time by Bill!
>
> With hindsight, it is now intuitively obvious to
> the casual observer (or more certainly, casually
> obvious to the intuitive observer), that I should
> have had the rotator bolts checked before
> five years had elapsed.
>
> And, now, with the awareness of the alternative
> bolts and safety wires, even at $50.00 for the
> package of six, I'd strongly recommend they
> be purchased if you install the Orion, and
> maybe for all rotators, and, periodically check
> your bolts!
>
> Photos of the original tower installation are
> in the lower left corner at http://www.mxg.com,
> and you can see the load on the Orion is most
> definitely non-trivial.
>
> 73,
>
> Barry, W5GN
>
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