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Hello Michael,

I have spent the past many months trying to tweak an inexpensive Celestron? CG4 to make it capable of
2-4 arc second autoguiding. Quite a learning experience.. It may even work !

I thought I would clean and tweak my GM-8 as it has not been used in a decade... thus staring this engineering
research project.

First Step : Fully Clean the worm and ring of all grease.. I like charcoal lighter fluid : a synthetic kerosene ..
low evaporation and odor and reasonably not overly flammable.

Mate the two manually and you will find there is a very precise position where both engage and that the worm
will be pushed outwardly either above or below this.

Reassembly the Ring Gear on Dry on to the thrust bearing and center hub.. Dry is the only way you can 'feel' what is happening with gear engagement. You need to install a manual drive shaft on the worm also.
( okay to lube the center hub of the ring gear - worm and spur need to be clean.

Press the worm into the ring and tighten first the Left worm-block and then the Right. If you can not turn
?the worm shaft manually, press a bit less and loosen and re-tighten the Right.? IF you can turn the
worm shaft go on to the next step.

Is the Ring Gear High or Low ?
IF you can Lift the Ring Gear away from the washer- thrustbearing-washer stack, the Ring is Too Low ( my case )
IF when you push down on the ring gear and the worm shaft jams .. the Ring is too High .

When you get close in your shim process, you will find the worm shaft rotates okay CCW ( pulling the ring downward
onto the bearing ) but jams CW as the worm tends to lift the ring from center. Always test CCW or press down
on the ring in CW rotation.? ( when the system is assembled, the ring will always have some down-load )

If the ring gear is High, it is an easy job to shim up the worm gear end bearing housings .. not so in my case

1) I have a set of brass shim similar to this?? 0.001" - 0.015"? in many steps of thickness


2) You need to cut it with heavy scissors ..? I just used 5 or 6 pieces between the upper thrust washer and the
bottom of the ring gear ( there Should never be movement between them ) maybe 1/4" x 1/2" or less in size.

AND , each small piece needs to be Flat . The brass? pieces curl when cut
I assembled everything only to find the gear worked in the CCW but not in CW : the curves in the
shims were acting as springs and pushing the ring gear away ( up ) from the bearing washer and jamming
the worm-ring.

WHEN you get everything close, you need to rotate the worm ( 180 times ? ) through a full rotation of the Ring
and adjust for the highest point. If the worm shaft starts to feel 'lumpy' and unsmooth, the bearings are being
overloaded ( Brinelling ) and the worm gear right shaft block needs to be 'relieved' a bit. Don't Overload The
Bearings or you will need to replace them ( as I did ) Just a minor adjustment should work.

Grease it all up and test it fully assembled.
I like a sticky heavy grease for the worm-spur ring gears. I used a thick? black moly-lube and Nye Heavy damping grease mix. The load on the worm-spur is extremely high and they move via sliding friction ..? Just paint it on the worm as you
manually rotate it around the spur to evenly apply.

IF I can figure out how to post photos on this site I will add a few.

I was concerned that having such a tight interface might jam at cold temps .. put the mount in the fridge over night ( with the manual shaft still on )? and although the grease got stiff, it worked smoothly.

The spacing was more critical than I expected.. a? 0.004 shim caused the worm to jam when I pushed down on the
spur,? 0.006 allowed the spur to be pulled upward.? I'll try it .. may need to back off on the worm-ring clearance, but the
'vertical' alignment? is now correct.

Regards,
Alex
Winter Springs Fla