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Servicing a Vintage Sears / Tasco 3" EQ Mount

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#1 Preston Smith

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Posted 18 April 2008 - 03:46 PM

[b] PAGE 1
Many who spend time hear in the Classic Telescope Forum have or may have in the future a Sears or Tasco 3” scope. The mounts can appear intimidating to take apart, clean, re-grease and re-assemble. There are a few traps to be avoided so the purpose of this thread is to give the reader a visual “how-to” restore one of these mounts and get at least 40 more years of use out of it!

There are some minor differences between the the Sears and the Tasco but nothing critical. The mount that I am servicing here is a Sears. I also have a Tasco mount so I’ll try to post some pictures tomorrow to show the differences.

I’d like everyone to weigh in on this thread. Let me know if you’ve encountered something different or if I don’t have something correct. If there is a good response I may consider turning this into an article for CN. I want to hear your thoughts and experiences! I have used some generic terms to describe many of the parts. If someone has a different name for a part, please state so. The best name for a part is one that everyone can quickly understand.

Here’s a picture of my newly acquired Sears mount that is dirty, crusty and is currently non-operational due to dried out grease inside the mount:

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#2 Preston Smith

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Posted 18 April 2008 - 03:47 PM

PAGE 2
For me, the best place to start is the clamshell. Remove the felt and remove the nut (counterclockwise). The clamshell hole is also threaded so you will have to rotate the clamshell counterclockwise or the declination shaft (clockwise) until the shaft separates from the clamshell.

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#3 Preston Smith

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Posted 18 April 2008 - 03:48 PM

PAGE 3
Be sure to capture the small bronze bushing plate that is under the clamshell and put it in a small cup or muffin tray so you don’t lose it. Hard to replace….

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#4 Preston Smith

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Posted 18 April 2008 - 03:49 PM

PAGE 4
There, three easy pieces. I would recommend that you leave the base on the mount at this time as it will greatly stabilize your operation.

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#5 Preston Smith

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Posted 18 April 2008 - 03:50 PM

PAGE 5
Why five screws? Weird, huh? But once you remove the cover you will see why. The four screws in the blue circles hold the cover plate on. The screw in the yellow box actually screws into the Right Ascension friction ring (or brake) inside the mount. The levered knob inside the yellow box is used to push the chisel tipped brass spreader into the friction ring (and expand it against the sides of the mount).

To take this apart, first remove the screw and knob inside the yellow boxes. That way you won’t pull everything apart when you take the cover off. Then take out the four screws in the blue rings.

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#6 Preston Smith

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Posted 18 April 2008 - 03:53 PM

PAGE 6
OK! Now you can see inside. Remove the gaskets and the small chisel-tipped brass spreader. Don’t lose this!

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#7 Preston Smith

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Posted 18 April 2008 - 03:54 PM

PAGE 7
Remove the friction ring and lift the Right Ascension Yoke off of the mount. A beautiful brass worm gear is now visible (the teeth are on the inside. You CANNOT slide the worm gear out at this time – don’t even try it!

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#8 Preston Smith

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Posted 18 April 2008 - 03:55 PM

PAGE 8

OK, HERE IS THE TRICKY PART!!!!!!!

The bearings (bushings) for the worm are NOT screwed in! I know, I know, there are two holes on each side of the bearings. You would naturally think that you need to unscrew them to get the worm out of the assembly. NOPE!

BEFORE YOU EVEN REMOVE THEM! Either take a photo or sketch the location of the holes on each side. It is VERY important to do this.

Why……(I knew you would ask)…see the next frame.

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#9 Preston Smith

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Posted 18 April 2008 - 03:56 PM

PAGE 9
Because the bearings are ECCENTRIC! Yep, take a look below. I’ve taken a picture of the outside and the inside of the bearings.

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#10 Preston Smith

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Posted 18 April 2008 - 03:57 PM

PAGE 10
There are four SETSCREWS that hold the bearings in place. This picture clearly reveals the dark dirty secret. Without this, you would be trying IN VAIN to get the bearings out!! (I know…..boy do I know!)

This picture is truly worth a thousand words!

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#11 Preston Smith

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Posted 18 April 2008 - 03:58 PM

PAGE 11
After you loosen the setscrews, slightly rotate the eccentric bearings to lower the worm down – away from the brass worm gear. Then you can slide the worm gear out of the yoke and look at all of that shiny brass (and old, crusty grease).

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#12 Preston Smith

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Posted 18 April 2008 - 03:59 PM

PAGE 12
Clean everything up and then let’s start to re-assemble.

Here’s a BIG tip. If this is the first time your mount has been disassembled since it left the factory then you have an easy guide to reassemble the bearings. Look for the indentations that the set screws made and you can easily realign the bearings to lift the worm up against the worm gear (once again).

However, if the mount has been disassembled many times then there will probably be multiple indentations. THAT is why you need to take a photo or sketch the original orientation of the holes in the bearings so you can easily realign everything. If you don’t do this, it will definitely take you some time (the voice of experience has warned you).

You may have to SLIGHTLY rotate the bearings just a few degrees from the original position to get the worm up against the worm gear. Be prepared to do this several times as you position the bearings and tighten the setscrews. Ideally, the worm will move very easy and there will be no play in the big worm gear when you turn the worm clockwise and then counterclockwise.

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#13 Preston Smith

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Posted 18 April 2008 - 04:00 PM

PAGE 13
While you are making final adjustments, I strongly recommend attaching the slow motion knob and cable. It’s a lot easier to turn the worm this way. Besides, your fingers will probably be too greasy to turn the shaft!

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#14 Preston Smith

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Posted 18 April 2008 - 04:02 PM

PAGE 14
There, all greased up and the friction ring has been re-installed. You can either place the chisel-tipped brass spreader into the indentation at this time or wait until you have placed the cover on and drop it through the hole in the cover. I prefer to put in at this time so I can be assured that the spreader’s chisel end is firmly seated into the friction ring.

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#15 Preston Smith

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Posted 18 April 2008 - 04:02 PM

PAGE 15
OK, put the cover back on. Your first screw should be the one that goes through the cover and threads into the hole on the friction ring.

Next, gently reinstall the levered knob on the opposite end so that the brass spreader stays in place. Just turn this knob until it seats the spreader against the friction ring. If you make it tight you will not be able to move the cover to line up with the holes for the remaining screws.

Now move the cover back and forth until the remaining four holes line up with the threaded holes inside the mount. Then install the remaining screws.

How tight do you make these screws? Not at all. I recommend just seating them initially and move the mount back and forth to see how much friction there is. Ideally, you do not want any slop or wiggle in-line with the axis but smooth movement around the axis so keep “tweaking” (tightening/loosening) the screws as you go.

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#16 Preston Smith

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Posted 18 April 2008 - 04:03 PM

PAGE 16
I took this picture so you can see the dried grease and how it was “caked” on to the bearing surfaces. Yuck! :vomit:

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#17 Preston Smith

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Posted 18 April 2008 - 04:04 PM

PAGE 17
As you remove the declination gear to clean it, I would recommend slapping a little bit of new grease to let is slide out easier. I would also connect the slow motion knob and cable to easily remove the gear once you have removed the nut and threaded bearing to save your fingers from doing a lot of hard, slow work.

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#18 Preston Smith

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Posted 18 April 2008 - 04:05 PM

PAGE 18
So here it is - the serviced mount! Not necessarily pristine as there are still a few (minor) scratches but this baby is now 100% operational – and will probably be for the next 40 years!

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#19 mikey cee

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Posted 18 April 2008 - 05:13 PM

Preston....Nice job! How much would you charge for this service? You probably could make few bucks here! :grin:Seriously tho' I got as far as the set screws and loosened them up quite a bit. But couldn't figure out the conical bearing hiding inside the casting. I thought maybe there was a groove that the set screws seated into. I knew you couldn't tighten the underneath pair 'cause that jammed the worm into the worm gear so tight that the cables wanted to "kink". After "enough" fiddle fartin' around I found the perfect pressure spot as I gingerly rotated the cables and tightened the bottom set screws. I then just snugged up the side set screws knowing they just might be for centering or alignment purposes instead of for preassure. Mine works so smoothly because my grease was just gummy and not "baked" hard. So I think not much will be gained for me to persue this again! I should get the "Fearless Fosdick" award tho' for tackling this thing before you did! :grin: :smirk: :p :lol:Mike :waytogo:

#20 Littlegreenman

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Posted 18 April 2008 - 11:17 PM

Yes, how much would you charge. Not for lack of screwdriver skills, (I did a few years in machine shops, even a bicycle assembly factory) but I'm just lazy!

I just got a Tasco version in that has a lot of slop and needs to be re-adjusted or rebuilt. Thank you very much!

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#21 Vesper818

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Posted 19 April 2008 - 12:56 AM

Great demonstration, Preston. Thank you very much. I have taken apart the simple E 1/2 mount for the little Micronta (same as your Astro 50mm mount, but have not tackled anything bigger.
You make this look as simple as cleaning and relubing a Singer Featherweight!

#22 ngc6475

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Posted 19 April 2008 - 12:14 PM

Thanks for the report, Preston! I have a very similar Tasco that has been lying around gathering dust and I may go after it now using your excellent advice and tips. :waytogo:

#23 Happy-Idiot

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Posted 19 April 2008 - 04:40 PM

Incredible job as usual Preston,:waytogo: how is the performance of these eq's? Stability,smoothness,dampening,and such?

#24 Preston Smith

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Posted 19 April 2008 - 08:17 PM

Mike: Preston....Nice job! How much would you charge for this service?
A lot! It’s quite a bit of work! :jawdrop:


Steven: I just got a Tasco version in that has a lot of slop and needs to be re-adjusted or rebuilt. Thank you very much!
Your welcome Steven.
I’ll post some pictures of my Tasco mount tomorrow as I left my digital camera at work! :doah:
There’s just a few differences. But removing the worm is the basically the same process.



Carol: You make this look as simple as cleaning and re-lubing a Singer Featherweight!
Thanks! But sewing machines scare me – they really do! :bugeyes: :scared:


Walter: I have a very similar Tasco that has been lying around gathering dust and I may go after it now using your excellent advice and tips.
Go for it Walter! :waytogo: Not much difference between the two although getting the cage of the Tasco is a little more effort.


Brian: Incredible job as usual Preston, how is the performance of these eq's? Stability,smoothness,dampening,and such?
Good Question Brian! I'll rate it near the end of my evaluation.

I took the mount out last night for a shakedown cruise. I got it set up on Polaris rather quickly. My target was Saturn. I figured it would be a good test of the mount since Saturn was so high. And I wanted to spend a lot of time watching our ringed friend.

Everything on the mount was a little stiff. But it is important to put the scope on the mount and run it through the paces. After about an hour everything started to work smoother. I noticed I was getting some play in the worm drive. That surprised me. In the morning I realized what was happening. I apparently didn’t do a good job of snugging down the set screws on the one side. When I would turn the slo-mo knob the one bearing would slightly push out the side (about 1/16 of an inch) and it gave the false indication that there was play in the worm. I tightened up the set screws and no more problems.

I tweaked the mount a lot today. The declination gear locking nut needed to be reseated – some play became apparent when I had the scope mounted on it. I also (very slightly) tightened the four screws that secure the right ascension yoke on the mount. That increased stability too.

So, on a 1-10 scale, this is how I would rate the mount’s performance now that I have revamped it:

Stability: 8
Smoothness: 9
Dampening: 8

These ratings are just for the mount. Everyone knows that the legs on the Sears and Tasco 3” scopes could have been designed better. Maybe I’m just fussy. BTW, One thing I did notice today is that the legs on my Tasco are slightly thicker than the Sears.

The most important thing to remember when revamping a mount is that you will need to operate your scope a few times and keep “tweaking” the mount. DO NOT get discouraged on the shakedown cruise. Just take good notes on everything that doesn’t seem right and then set the scope up the next day so you can visually see what the problems are.

Now that I have the Sears and Tasco 3" mounts done, I have two Tasco 7TE-5 mounts to do. Guess I better take more pictures! :grin:

#25 mikey cee

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Posted 19 April 2008 - 11:58 PM

Preston....I found that the mounts improve greatly if you ditch the legs and mount them on a metal pier. No comparison for dampening and accessibilty. :smirk:Mike

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