Hi Ken,
That narrow bearing you mentioned is a thrust bearing and it is indeed made of
‘unobtaneium’.
But, there are an additional six bearing in that assembly that are made of the
same material.
In the large, low speed planetary gear assembly there are three ‘planet’ gears,
each on a thick shaft, and each shaft has a bearing on each end. These bearing
are identical to currently manufactured bearings EXCEPT they are only 11mm
thick, where the standard ones are 12mm thick. Fortunately, if they are bad,
since they are in a low speed area, they could be replaced with sintered bronze
bushings.
It is my understanding, these bearings were especially made thinner to reduce
the overall size of the complete assembly.
I have a trick that will absolutely keep the water out.
I tried the addition of another seal internally, as was recommended by many,
and was not impressed.
73 de Steve, NR4M
Sent from my iPhone
> On Jul 22, 2023, at 7:52 PM, Ken K6MR <k6mr.mail@gmail.com> wrote:
>
> I worked for a guy in the 1960s (W6HX) who built prop motor rotators as
> part of his antenna installation business. The top gearbox seal does
> nothing to keep water out. The only way to keep the rotator dry is to have
> a sheet metal "dog house" on top of the rotator plate surrounding the
> entire top area. His design had a selsyn as well as mechanical stops and
> electrical limit switches which were all covered by the dog house. A sheet
> metal overhang seal was on the mast to seal the top of the cover where the
> mast passed through the top.
>
> Prop motors are not difficult to rebuild if the bearings are still
> available. I have not tried to find any for at least 40 years so I don't
> know. All the bearings have model numbers stamped on them for easy
> identification. The only bearing that was not available last I looked was
> the large bearing that the bevel gear sits on.
>
> *Ken K6MR*
>
>
>> On Sat, Jul 22, 2023 at 2:49 PM <john@kk9a.com> wrote:
>>
>> Some people have really good luck with K7NV prop pitch rotators and others
>> like you have water related issues. I do not know what the seal looks
>> like.
>> I do know that Kurt wanted the full weight of the mast and antenna on the
>> rotator to seal the gear box, I am sure that you heard this and tried it.
>> It
>> is sad to hear that you have had so many rotator issues with the expensive
>> rebuilds. That is not what you except out of a prop pitch. Two of my prop
>> pitch motors are driving K0XG rings and those motors have the gearbox
>> facing
>> downward so they have different water proofing methods (I hope).
>>
>> John KK9A
>>
>>
>>
>>
>> Paul Christensen w9ac wrote:
>>
>> I own a RT4500HD but waiting on cooler weather for installation. It seems
>> robust enough as it's replacing a small form-factor prop-pitch. Between
>> excessive water leakage after rebuilds and K7NV now SK, I was looking for
>> an
>> alternative. The reliability of prop-pitch rebuilds has been
>> disappointing.
>> N4CC and I have been changing them out every 1-2 years at a cost of $2,500
>> per rebuild. Crazy. We have a prop-pitch "graveyard" at our remote site
>> with something like six prop-pitches needing repair.
>>
>> What seems to happen is that water ingress is caused by excessive surface
>> heat in the Florida summers, followed by cool rain. This creates a suck-in
>> effect. Because a prop-pitch is mounted upside-down in a tower, the seal
>> needs better protection without having to resort to a special covering. In
>> this regard, the DXE rotator seems much better. In fairness, the
>> prop-pitch
>> was designed for a different application. But yes, only time will tell.
>>
>> The first DXE rotator installation will turn a full-size 4L M2 40m monoband
>> Yagi at 140 ft and a 9L M2 6m Yagi at 155 ft. Both antennas are mounted on
>> a 3-inch chromoly mast. This fits within the DXE design spec. In
>> preparation for the installation, we used a crane back in April to change
>> out a Rohn 3-inch thrust bearing with the equivalent type from DXE. The
>> DXE
>> bearing seems much more robust.
>>
>> Paul, W9AC
>>
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