Old Style PST-61 disassembly

(Updated 0447Z October 20, 2012 )

This rotator was installed late in the Summer of 2001. So this is what a leak can do in less than five years.

Read this tutorial completely before staring disassembly.
When ready to start disassembly, move to the Disclaimer which follows Photo 5 and proceed from there

. If some point is not clear, or might be better reworded, drop me an e-mail.

Added Note on PST-61 information and CAUTION:

Although the  ratings for the PST-61 are listed below, I've had it pointed out to me that there are only 4 bolts holding the housing to the base.  These are about M5,  or slightly under a 1/4". According to e-mails and calls I've received that the housing is not capable of handling a 40 ft^2 antenna load under windy conditions.  I was shown several photos and in each of those the housings displayed the effects of severe corosion from salt water corosion and at the time it was attributed to that. None of the PST-61s I've repaired had problems in this 4 bolt attachment to the base area. These 4 bolts are extensions of the stand offs shown in photo 21.  That may mean these rotators were not used at near their limitations, or the problems were anomolous.  However additional e-mails and calls  information leads me to believe that the weak point is likely the 4 bolts that are threaded into the housing made of cast Aluminum. One e-mail flately stated that a 40 foot boom on a 5 element, 20 meter monobander was just too much for the rotator. I have not run tests to substantiate tht claim, but nave no reason to doubt it. To me that means the housing may be the weak point and not capable of handling the load that is well within the gear train and motor ratings.  I will spend some time this week getting additional information.

Not having figures to bear the above out I'd approach the maximum ratings of the rotator with extreme caution.

I've seen wind area loadings listed from a bit over 36 ft^2 to the 44 ft^2 listed below.  The tableis taken from the RF Solutions page  http://www.rfsolutions.com.au/products-page/prosistel/big-boy-pst-61/ 

Wind load area 4.1 m2 44.1 sq/ft
Rotating torque 3800 Kg/cm 3298.02 in/lb
Braking torque 29000 Kg/cm 25169.1
Vertical load 850 Kg 1870#

 

Photo 1
Rotator output shaft with bottom bearing to the right.  The upper bearing and housing cover are to the left. Note corrosion on upper bearing. Once cleaned the bottom bearing does show some play, but I don't know if it's out of tolerance or not.

The problem is the need to take the top bearing off to the left, but the blue plate (housing top), plus the welded flange is in the way.

Now with a bit more information. The end of the shaft (bottom) that fits over the end of the position pot (to the right in the base of the housing) is really two concentric shafts. One is the bottom end of the worm gear wheel on which that taper bearing mounts. The other (See Photo 13) goes all the way through and has the plate welded on that takes the mast clamp (to the left in the photo). The inner shaft is: pressed in, keyed, and held in place with a snap ring  The ends of the two shafts were covered with an RTV like substance which hides the snap ring. Note too, that the bronze gear is cast onto the steel support and is thicker than the steel support.  REMEMBER this when it comes time to press the shaft out of the gear. Do not put pressure on that bronze gear!  That gear is expensive, comes from Italy, is difficult to get, and takes forever to get here if you do find one.  Maybe some reader will find a stock, metric gear available some where. If so, please e-mail me.

 

Photo2
NOTE Shaft is standing on its top (IE it's upside down)
Top bearing showing damage with some roller separators missing.  Pieces were wedging under the rollers causing the rotator to freeze up. When I typed this I had not been able to get the top bearing off the shaft as there is a plate wended on the end of the shaft on the other side of the top plate. Once the inner shaft has been pressed out the bearing race is *relatively* easy to remove.  The housing TOP Plate is the blue object at the bottom of the photo.  NOTE minor wear on brass worm gear teeth which shows as different colors on the teeth to the right side of the image.

 

Photo 3
Brass spalling on large worm gear. There are several possible reasons for this.  One is the tremendous pressure that would have been exerted when the output shaft bound up whether it was the internal bearing or the thrust bearing at the top of the tower. Another possibility would be the abrasive residue from the disintegrating top bearing.  I'm open to other suggestions.

 

Photo 4
Above is the top of the output worm gear wheel.  The pitted surface is where the top oil seal is located.  If you look closely you can see a band in the middle where the oil seal actually sets. The shiny area is where the inner race to the top bearing is seated.  Compare this to "Image 2" that shows the bad bearing still in place. The pitted area on the shaft above is the same area that shows the rust colored area showing the circular patterns in the referenced photo.

 

Photo 5
The bottom of the output worm gear wheel.  The rough surface is where the bottom oil seal is located.  Although rough it is in much better condition than the top. The groves show where the edges of the seal run. This would have been to the right in "photo 1"

Disclaimer: I take no responsibility for the results of others doing things the way I have done! This is what worked for me.

BEFORE starting at step 1,  a list of some things to remember:

The rotator used in this instance is the "Old Style" green PST-61 with the AC motor. This procedure may not be applicable to other versions.

Successful disassembly takes patience.  Do not be in a hurry! This is truly an example where "haste makes waste".  If you don't know, call some one and ask. I would add the CAUTION: When you get to that portion of the disassembly on some units the output shaft may think it has become part of the shaft into which it has been pressed.  It it does not want to come out easily in the press, dose it well with PB-Blaster and let set for at least 12 hours if not 24 before proceeding. IF after a good soaking it still does not want to come out I seriously suggest enlisting the help of a good machinist or mechanic who has experience with this sort of thing.

Find a work area large enough to hold all the parts laid out in order. The work area needs to be clean and one that can tolerate oil and grease. It also needs to be easily cleaned!

Lay the parts out in order on paper towels as they are removed.

At this point I'll repeat, Put an ALIGNMENT MARK across the top, down the side and across the bottom of the housing and end covers BEFORE taking anything apart!  To make life simple, before disassembling the rotator temporarily connect the control box and power up the rotator. Set it to mid rotation. Pot removal is step 4.

NOTE there may be some very thin metal spacers in there under the bearings. Don't lose them and remember their location. You may or may not need them with the new bearings.

These are large worm gears with a deep grove.  It will require removing all the bolts from both covers to allow the worm gear wheel to be moved sideways before it can be removed from the gear box.

Remove the motor and smaller worm gear reduction unit then remove the cover over the other end of the large worm gear. Be careful of the hardened steel worm gear. It most likely will have some very sharp edges that can give some nasty cuts.  It should remove easily by lightly tapping on the end. Do not try to drive it out! If it takes more than a light tapping you are going the wrong way. Remove it AFTER the worm gear wheel has been removed. NOTE this worm gear comes out of the housing on the side *opposite* of where the motor mounts.  

Remember the bronze gear may be massive and appear rugged but is not meant for side pressure and is *relatively* fragile from the side.  Don't use it as a mount to push against when pressing out the inner shaft. Dropping it would also likely ruin it.

PLEASE NOTE: The inner shaft is held in place by a snap ring at the slotted end by the position potentiometer, is a press fit, and is keyed.  Remove the snap ring, soak in penetrating oil and let set. (The snap ring may be covered by a layer of Silastic RTV making it invisible until the RTV is removed) Reference Photos 6 and 7 for the snap ring and Silastic RTV covering.

You need to remember the position things were in when you started.  Take photos and don't be afraid to use a felt tip marking pen *liberally*

Treat the gaskets with respect.  New ones can be made of regular gasket stock, but only if you know how and have the material which can be found at most automotive and hardware stores.

Invest in a can of good penetrating oil.  I happen to like PB-Blaster even though I have used WD-40 by the gallon (It's cheaper that way).  After a thorough cleaning hit all the areas on the assembly shown in photo 1 liberally with a penetrating oil. Then let it set for 12 to 24 hours.

Pressing out the inner shaft is at least a two man job. It's not difficult, there are just too many things for one person to hang onto while pressing and even more when it comes apart. Do not let the worm gear wheel fall onto the floor. It's expensive!  Hold onto everything and don't pinch anything important.

 

STEP 1.    Make sure the motor and gear box are free of dirt and grease (IE CLEAN!) and the work area is clean.

2.    Remove the drain plugs and drain the larger gear box. Do this in an area where nothing will be damaged if the oil splatters, or spills.

3.    Remove the motor and smaller worm gear reduction unit from the larger by removing the 4 small bolts. NOTE it may require tapping on the smaller reduction unit with a rubber or wood mallet to get it free. (DO NOT use a metal hammer!)

NOTE: Before the next step remember there is a 10 turn pot in the bottom of the housing connected to the bottom of the output shaft.

4.    Remove the bottom cover taking care not to damage the position potentiometer. There is a pin through the shaft that slips into a slot in the bottom end of the output shaft. on some rotators this pin is a press fit and loose in others  This is going to give you a few pieces awkwardly connected by the cable. Keep track of the shaft position of that position potentiometer. IE count the turns from one end or the other CW or CCW and WRITE IT DOWN!

Another NOTE: It's been brought to my attention that some of the bolts (cap screws) holding the base onto the main housing  MAY require the use of an Allen wrench that has been shortened to fit and particularly the one over the feed through for the wires going to the position indicator pot. These wrenches are made of a very hard metal that is difficult to cut with a saw.  A small abrasive cutting wheel is most likely the best method of shortening the wrench.  Do a nice clean cut with a flat end and a slight bevel to the sides to aid in inserting the wrench.   Do not overheat the wrench while cutting.  (Wear a face shield as there will be small bits flying off the cutter )Its also my understanding that the "stand offs" that hold the base cover in place (Photo 21) in some other versions of the rotator serve to hold the base onto the main housing.

5.    Remove all the bolts holding the top and bottom covers on the larger gear reduction unit. Again it may take some tapping to free the covers from the gaskets. Move the output shaft to the side in a direction away from the worm gear. The worm gear fits down into the worm gear wheel. This requires the the worm gear wheel be moved away from the worm gear so it can be pulled out of the housing. Hang onto the bottom cover as there will be nothing holding it when the shaft comes out of the oil seal.  This should result in something akin to photo #1.

Photo 6
The gear and shaft after removal and a bit of cleaning. This is the bottom end of the shaft with the slot that fits the position indicating pot complete with lots of RTV.

6.    The plate to which the mast mount attaches is welded to the end of a shaft. This shaft goes all the way through the gear assembly and has a slot in the end for the position pot coupling. The shaft also is held in place by a snap ring and is keyed with a key that is roughly 3/8" square (it's metric) and about 3" long.  The bottom end of the shaft is probably coated with an RTV like substance which also covers/hides the snap ring. See Photo 6 and 7.

7.     Remove the RTV like substance, the snap ring,  and thoroughly clean the end of the shaft.

Photo 7
There's that hidden snap ring with the key slot just barely visible at the top after the removal of the RTV.

8.    Remove the bottom bearing. It should come off easily although there may be some residue on the larger shaft that must be cleaned off to allow the bearing inner race to slide off easily.

9.    Remove the rollers and retainer for the top bearing.  This is mainly to prevent dropping them while pressing out the inner shaft.

10.    Liberally apply a good penetrating oil to the bottom end of the shaft into the key slot and around where the snap ring was located.

11.    Let the whole works set for 12 to 24 hours or at least over night.

12    Press out the inner shaft:  Resist the temptation to use the brass worm gear wheel as something to push against.  The brass is cast onto the steel support so use the steel support. We split the inner race of a taper bearing and placed the halves between the steel portion of the gear and the press support.  The inner shaft pressed out easily while one set of hands were under it, one set were holding things in place, and a third set operated the manual press. This takes care not to damage any parts or fingers.  Once the inner shaft has been pressed out, wipe it clean and set it aside.  Remember that bronze gear is expensive, hard to get, and comes from Italy. It may take months to replace if broken.

 

Photo 8
Note the shaft and keyway. That is the shaft that is pressed down and out of the gear hub. Carefully clean all the RTV residue out of the grove and apply the penetrating oil here.  PB Blaster is one of the better penetrating oils. The "U-shaped" support mentioned above fits on on the bottom of the gear against a shoulder identical to the one shown here or supports are inserted between the steel gear flange and the press. PLEASE note the very thin spacer on the visible shoulder (don't lose it, or them). When the new bearings are installed these may or may not be needed. Although unlikely you might even need an additional spacer or two.

 

Photo 9
Please note in the photo below: The assembly is setting upside down on the rotator top flange.  The central shaft (with the slot) has to be pressed all the way through the gear hub and bearing. 

13.    With the inner shaft out of the way slip the top gear box cover over the shaft, clean it, and set it aside.

14.    This gets us to the top bearing removal.  The bearing may or may not come off easily. In the case of older rotators which may have had some water get in (which is likely), or the top seal fail as in this particular example the bearing may consider itself to be part of the outer shaft (see photo # 2).  At this point make sure the shaft beyond the bearing race is clean. In photo #2 there is a thick brownish yellow layer of gunk (rust, lube, and water) that needed to be cleaned off. If you can not move the inner race by hand, give it the penetrating oil treatment and let set for a while.  Both the top and bottom of the race have flanges. One of the wide flat bearing, or gear pullers may work well here. It may be necessary to make a "U" shaped plate that will fit closely around the outer shaft and the larger diameter flange on the race is set up against this.  Just tapping on this with a dead blow hammer should cause the race to slide off. Other times it may be necessary to grip the flange in a vise, but be warned, the tighter you grip the flange the tighter the race will grip the shaft. I used the vise and a 1/2" thick piece of soft copper between a 5# Engineer's Hammer and the end of the outer shaft.  Make sure some one hangs onto the gear while doing this.

Now it's time to inspect the top and bottom bearing flanges which are also the surfaces against which the seals ride.  The photo on the left is the top sealing surface and the one on the right the bottom sealing surface. It takes little to realize a new seal isn't going to work against that surface shown on the left. Even the one on the right isn't all that great. But luck is with us, at least in this case.  The rotator uses a standard size "double lip" metric automotive seals. These automotive seals come in under-sizes. Unfortunately here is the States you may only find the single lip seals, but try the on-line supply houses if you don't find any locally.  IF need be you can get by using the single lip seal.

Now you have to have the surfaces machined down on a lathe or grinder. Although the one on the left looks really bad it only took removing 0.5mm of metal to get a mirror finish.  I chose to take the same off the other end to use the same size seals which would be 1 mm undersize.

Note that all of the housing and gears are CLEAN and dry at this point.

photo 10 Top                                                                                   Photo 11 Bottom

15.    "IF NECESSARY" remove the oil seals from the gear box covers: If water has gotten in they will need to be replaced!  Set the covers on convenient size wood blocks. 1/2" to 1" thick is plenty. You should be able to easily tap the seals out (toward the inside of the covers) by using a small hammer and a dowel or large screwdriver to *tap* the seals out of the recesses.  Never use the hammer directly, tempting as it is. It only takes a slight miscalculation in aim to ruin the gear or housing.

16.  To replace the seals in the now *clean* covers coat the outside surfaces with a thin coat of grease, position the seal in the opening with the channel to the inside.  Take a clean, flat piece of wood or metal and press the seal *straight* in until the outside surface is flat or flush with the top of the housing. Put a thin coating of grease on the inside of the seals as well to aid in fitting them over the shaft.

Photo 12
Top Plate with new seal in place. Note the depression around the seal as well as the shape of the seal being ideal to hold water in place and no way to drain it. When reassembled the area inside that reinforcement ring is packed with White Lithium grease.

From here on the assembly is pretty much (more or less) the reverse of the disassembly.

Photo 13
I installed the worm gear and then the sealed bearing. The bearing is a snug slip fit so it has to go into the casting straight and the shaft by itself is not quite enough. I slide the new bearing down the shaft, then slid the old bearing over the shaft and used it to gently work the new bearing into place.   Shown to the right of the rotator housing is that center shaft with the rotator top plate.  YES that keyway is crooked! There is a straight one on the other side.

 

Photo 14
Old bearing on casting with new bearing fully seated.

Photo 15
New bottom bearing in place. The position indicator pot and key can be seen through the opening.  Be sure to remove the plate holding the pot and the pot before inserting the shaft.

 

Photo 16
The top "wheel bearing" is slid into place on the shaft and packed with the White Lithium grease

 

Photo 17
Next the worm gear is greased

Photo 18
And the center shaft is pressed into place. (don't forget the key and snap ring)

 

Photo 19
This assembly is then mounted on the main housing. Due to the size of the worm gear and worm gear wheel, the assembly is slid in away from the worm gear until the flange is in place. Then the whole assembly is moved back so the worm gear wheel engages the worm gear.  A couple of bolts hold the cover in place.

 

Photo 20
The whole area is packed with grease  right up flush with the bottom before installing the bottom plate.  Remember to remove the pot and to thoroughly grease the seal before sliding the bottom plate into position. NOTE the slot position and position it the same as it was when removed so it lines up with the bottom housing plate marks made before disassembly.

 

Photo 21
Bottom in place with pot and cover ready to be installed.  Remember the alignment marks and the number of turns on the pot from one end or the other.

NOTE, when installing the motor it may be set in almost any position to fit different towers.

If the rotator was reassembled using the guide marks the direction alignment should be relatively simple.

 

Adendum:

I'm going to have to reorganize this a bit, but I've had questions as to how I handled the water problem with the top seal and bearing failure.

I created a disk of silicone rubber to keep the water away from that troublesome depression on top that causes water to rust the output shaft which ruins the seals which lets water into the houseing which ruins the bearings. Actually it's two layers of rubber with the cuts off set and bonded using Silastic RTV(TM) rubber.

Step1: I found the local hardware store had rubber sheets that were just the size of the rotator main housing OD. So I found the center and carefully cut out disks that diameter. IF you live in an area where ice is common this disk should be at least 2 inches wider to prevent it from freezing to the top of the rotator around the edges.

Photo 22
Marking the Center
 

Photo 23
Finding the center for disk #2

 

   

 Photo 24
The cutting is pretty straight forward and not at all critical

 

Photo 25
Measuring the output shaft diameter to cut the proper side hole in the two disks. Note the flange on the output shaft below the calipers.  The idea is for this to keep water off the central seal and shaft which it doesn't.  This entire area between that inner reinforcement ring and the shaft under that flange has no where to drain so I pack it full of white Lithium grease under the rubber cover we are constructing.

 

Photo 26
One sheet with hole and slot cut.

 

Photo 27
Checking the fit

 

Photo 28
More fit checking and overlapping the disk edges to create the cone shape

 

Photo 29
Cleaning the shaft to get a good bond with the Silastic RTV (TM)

 

Photo 30
Adding the initial Silistac RTV(TM)

Photo 31
A good view of the final moisture/water cover.  The area over the center seal (central recess) is packed with White Lithium Grease to prevent condensation. I would have liked to have made the disks about 2" wider in diameter and with a bit steeper slope. One joint is visible but they are staggered so the other is not visible. Remember the entire area between the inner reinforcement ring in the top cover and the output shaft is packed with White Lithium grease.

 

Photo 32
The bottom seal showing the coupling slot which couples to the 10 turn pot for the direction indicator.


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