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Hi everyone,?
Just thought I would post my experience with renewing the main DEC shaft bearings on my G11 I have here in Australia. Its an older unit (2004) and originally a Celestron branded unit but is pretty much the same mount that was made direct by Losmandy at that time and similar to std product (even now).

I have been bringing the mount up to scratch over the last few weeks.? Generally its in good condition but a bit 'tired'.?

Updates so far:-
1 - Replaced gearbox
2 - Replaced oldham coupler?
3 - Replaced Worm with Brass high grade worm and also the OPW housing.
4 - Added the DEC/RA, extension removal pieces
5 - Knew clutch knobs with teardrop.

Each time got an improvement in Guiding, but hit a brick, wall. at around +/-5 Arc and it did not seem to be 'cyclic' but appeared more like 'noise', very random.
?
RA was very good but DEC was poor in comparison. I have cleaned (flushed) all bearings and re greased (slight improvement). finally I took a very close look at the DEC needle bearings on the main axis. after removing all the grease it was clear the lower bearing had some 'rust' on the needle rollers. You could not see it with grease on. Main shaft looked ok. I ordered the bearings from Losmandy which were not too expensive.?

Checked the web for anyone doing this before and couldn't really find anything.

Here was my process.

1. Isolate the lower DEC assembly.
2. Remove Gearbox/Motor/Worm drive assy
3. Remove the rear clutch tensioning nut and spacer bearings etc.?
4. withdraw the main DEC shaft.
5. I additionally removed the worm drive mounting plate to make handling the tube assembly easier.

You can see the two needle bearings, the lower bearing is basically flush (or just under) to the bottom of the tube and the upper bearing is at the bottom of the brass bearing on the upper side of the tube.

Thinking which one to remove I thought I would pull out the lower bearing with a 'pilot' bearing puller and the Push out the upper Bearing/Brass assy with a press and dolly. (from the underside)

After a bit of fiddling and getting a good grip on the lower edge, the lower bearing it came out.?

I 3D printed a 'dolly' which fitted down the tube and had a shoulder on it to pick up on the upper bearing. Inverted the tube and pressed out the bearing which basically pressed out the brass tube with it. So I had the bearing inside the brass tube. After making Making another dolly (3D printed) and drop I pressed out the bearing from the brass bearing tube.

Now both bearings are out I cleaned up all the assemblies and basically assembled in reverse.

CAUTIONS......

• NOTE THE BEARINGS ARE NOT BI DIRECTIONAL. there is a bevel on one end and a flat on the other, I am assuming that the 'FLAT' is there to make it easier for a puller to grip so make sure you get it the correct way around. ( if you want to remove it at a later date). Bevel faces out.
• When pressing in the lower bearing do not go more than flush or just under to the bottom of the tube. Internally there is an undercut to assist with removal. if you push it in too far you will have great difficulty in removing it with a puller as you wont be able to get 'under' the bearing.

1 - So I pressed in the new upper bearing into the brass tube first (another 3D printed dolly') and made it just under the edge. Again make sure you get it the correct way around.?
2 - cleaned the upper recess for the brass tube and then lightly lubricate and press in the brass tube until it hits the internal shoulder.
3 - Flip the tube and then press in the lower bearing just below the lower edge. (get it the correct way around)

To do this job I purchased a 'PILOT bearing puller' which was approx $35.
I also bought myself a 12T hydraulic press form local trade tools outlet for $150. ( Decided to bite the bullet on one as I needed one and every year I end up trying to press bearings.)
3 x 3D Printed ABS dollys (which worked better than I thought).

Having just finished thought I would record it as it may be useful for others.....

Pictures?

• Old removed bearings and ABS printed 'Dollys'
• Close up of old bearing showing surface 'rust' contamination.
• Extracted lower bearing using Pilot Bearing Puller
• Upper Bearing and brass removed from main tube
• Pressing the New bearing into the brass tube./bearing. Showing dolly used

All the best to everyone.

Pete

Well done Pete. ?I’ve got to do my bearings soon. ?Good to see another Aussie at it

cheers
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Brendan

Peter.? Good job. I've got a similar vintage G11 which I've fixed up a fair bit but still seems to havesome random nonsense. Are the bearings the same as those currently on the losmandy website? Might be worth a try!
Thanks Chris

That's interesting work Peter! Most don't bother to do the extra work to get to the shaft bearings which are hard to remove. You figured out there is no clear way to get a common tool behind the lip of the old bearing. I found this bearing puller kit (see pic) on Amazon USA which can be found under many different brand names but is usually the same. But I'm surprised you had had such a hard time getting the new ones in - I was able to just tap them in with a rubber mallet without much resistance. Some of us have opted to use this McMaster-Carr replacement part: which holds more grease and the needles do not overlap and touch each other. My preference was to relube with Mobilgrease 28 aircraft grease over the HGM standard Jet-Lube Artic. The thrust bearings also wear over time, and the underlying thrust washers can get grooved out over time from depletion of lubrication. The Jet-lube MP-50 is what the factory applied in this area which supports most of the mount and payload weight.?

If you are at +/- 5 a-s peak to peak without guiding this is pretty good. It all depends on the frequency. The dreaded 76s worm bearing error is a bugger to get rid of, which is why we do the Belleville washer upgrade.

Good luck,

John


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Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, Sequence Generator Pro and PixInsight user