LRod wrote:

On Tue, 13 Sep 2005 19:27:20 -0400, Marshall Goldblatt
wrote:


I have a Tailtwister (TX-2) rotor mounted on a Rohn 25 foldover tower.
While the tower itself appears to have survived intact, hurricane
Katrina snapped the mast and destroyed the antennas. I need to fold the
tower over to work in it, and likely leave it folded over for a fairly
extended period. This will leave the top of the tower and the rotor
upside down. Unfortunately, it is still the rainy season here, and the
last time I needed to do this, rain water got into the rotor and settled
in the bell, causing rust and other corrosion damage inside the rotor,
because it is only weather protected when it is upright. I would like
to seal the rotor to prevent this from happening again, but none of the
ideas I've had so far (wrapping it in plastic garbage bags, using duct
tape, using sealing foam) are usable, either because they don't seal
well enough to keep water out or because stuff may get up inside the
rotor where I can't get it out.

So, does anyone have any suggestions?


First off, there are at least two rotor repair vendors whom you should
contact for ideas; Craig's and RotorDoc (I think those are the
names--a web search should yield results).

Have used both over the years (at least one and perhaps both on this
particular rotor :-)). I don't believe that either had specific
suggestions for this problem.

Secondly, with some experience with HAM type rotors I would suggest
that the two principle entries for moisture are at the cable
attachment point (either a terminal strip or an Amphenol connector,
depending on vintage or whether you modified it), and the space
between the fixed portion of the rotor (the part with the cable
attachment) and the black rotating part.

The unit has a terminal strip, but this was "remoted" via a short cable
the last time one of the rotor repair vendors overhauled it, and the
point that the cable exits was heavily sealed. (This was done because
the terminal strip is blocked by the Rohn rotor mounting plate.) The
space between the fixed and rotating parts is the one of concern.

The cable attachment point will be trickier, but you may be able to
get good results with gobs of plumber's putty. What you want to avoid,
particularly if you have a terminal strip, is glopping it up with
silicone sealant or Coax-Seal. You will rue the day you ever tried
either if you use it on a terminal strip. The spaces around the
attachment into the non-rotating part need to be sealed, too.

You might also have success with plumber's putty at the opening
between the moving and non-moving parts. Just roll it up and stuff it
in.

I'd have some concern about some of the putty getting into the bell of
the rotor, where it could cause problems. I'm currently thinking of
using tape (perhaps just masking tape) to cover the opening, and then
covering this with sealing foam or something else. The tape would be to
prevent any of the sealer from entering the bell.

I would follow that up with some sort of shroud. The garbage bag/duct
tape method you mentioned seems like a really good idea. I would have
been inclined to think it sufficient without any extra caulking. Don't
be concerned about "stuff [that] may get up inside the rotor where I
can't get it out." See below.

Just garbage bags and duct tape isn't really sufficient (or hasn't been
in the past) because the way the rotor is mounted on the Rohn (seems
to?) preclude wrapping it well without gaps that let rain in.

As far as Dan's warning about the grease, I think he's right about the
"old-wive's tale." The rotator turns at 1 RPM. Even if the grease did
run out of the races (there are two in the T2X), you can certainly run
the rotator at least a limited amount of time without concern until
you get to it, not to mention that fact that there will be a film of
it that will stay on regardless of position.

Haven't ever had (noticeable?) problems with loss of grease.

What many people ignore is the instruction right in the manual
regarding grease, and it calls for very little. It's not a wheel
bearing. Since you're almost certainly going to want to take it apart
for a cleanup after all of your other repairs are completed, you can
take care of any missing grease (and "stuff") then.

Actually, no plans to take it apart (hence the concern about "stuff"
getting in). It was overhauled after tower damage _last_ year (not
directly hurricane related, but...). As far as I know, there are no
current problems with the rotor, so if at all possible, I had planned on
leaving it mounted, and just replacing the mast and other thing above.

There are two kinds of hams: those who have had bearings on the floor
and those who have never taken apart a HAM style rotor. But, even if
you don't get 'em all back in, you'll be okay. When you talk to one or
the other of the rotor repair guys, order a pack of extra balls.
You'll need 'em sooner or later anyway. Think of the fun you'll have
telling people you ordered extra balls.

Well aware of bearing on the floor :-)...

Here's a tip: the bearings are held in a plastic carrier. Whatever you
do, when you lift the carrier out, do NOT attempt to straighten the
carrier into any bigger diameter than the race it rests in. In fact,
keep the ends of the carrier overlapped. That is the secret to keeping
the bearings off the floor. It's not foolproof, but it'll certainly
reduce your adventure significantly. I can't tell you how many rotor
invasions I had to perform to learn that.

I hope your Rohn 25 isn't one of the ones that folds over halfway up
with a significant boom to crank it over. Those things are killers. I
had a friend in Oswego, IL, who broke his arm when repairing his after
it went over during the Plainfield tornado. The kit for 45 is MUCH
stronger.

It indeed _is_ a half-way up fold-over. No other style works in the
location (well, at one time in the distant past, I had a crank down,
fold over at the base tower, but current versions of such either won't
fit the space or won't fit the budget...) Have had it and folded it
over many times for many years without problems (lost it in hurricane
Andrew, but no problems for 10 years before or after that). However,
have lost the hinge section a couple of times in the last few years -
once because a wind gust spun it sideways while it was being cranked up,
and once because the boom got caught in a guy without our noticing while
it was being cranked up. I'm a lot more concerned (and careful) about
it now than in earlier years, but (for the above reasons) don't expect
to do anything about it if it can be avoided. We've avoided injury by
keeping well clear while it is going up and down, and (trying to)
control rotation by using guide ropes well to the side and out of the
path. The 45 _is_ much stronger, but it would be difficult to fit, and
would require replacing the entire tower, which is effort and expense
that isn't viable right now.

Good luck on all of your recovery.

Thanks!

Marshall