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Starfinder GEM clutch problems

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#1 hottr6

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Posted 18 March 2013 - 05:14 PM

I disassembled my Starfinder GEM for a strip-clean-and-relube, but when I assemble the RA clutch, it does not slip.

Is there a trick to re-assembly? Do the teflon bearings need to be dry-assembled? I suspect that the thin teflon strip that assembles between the inner-and-outer rings of the clutch is binding.

:question:

Shane in gray-zone NM

#2 apfever

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Posted 18 March 2013 - 06:24 PM

That strip is a trick to get in. It will often slip out a little, forwards or backwards, then it can fold over and bind up. You can examine it in place, before you put the front cover over the gear. It should be even and flush with the face of the gear.

I do not use any 'greasy' lube, I use a dry Teflon spray lube that leaves no residue except the Teflon powder.

#3 hottr6

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Posted 19 March 2013 - 07:21 AM

OK, thanks. I'll keep persevering. I'll also clean off the grease I used and try dry-fitting with teflon spray.

Shane in gray-zone NM

#4 hottr6

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Posted 21 March 2013 - 11:16 AM

OK, got it fixed. Wish I had made a movie, or even simple stills, to show how I did it. But ya know how it is... get excited and all thoughts of documentation fly out the window. :foreheadslap:

I had been trying to reassemble the clutch by simply pressing the pieces together. I even used a shop press because I thought the slip-ring was askew causing the binding.

In the end, I assembled the clutch by "screwing" the clutch plate and slip-ring to the hub. Make sense? Nope! OK, think of holding the hub in one hand, and the clutch plate/slip ring in the other like you would hold a jar of peanut butter, and then screw the lid onto the jar. Same action, but screwing the clutch plate/slip-ring onto the hub. Popped right on!

I thought maybe it was just luck that it worked, so I pulled it apart and repeated the peanut-butter-lid-screw trick. Worked again!

This mount is now as smooth as a baby's bottom!

#5 apfever

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Posted 21 March 2013 - 12:19 PM

Stupid me.

I didn't think to tell you about twisting the gear onto that hub with the thin Teflon strip between them. It's almost impossible to just directly press it straight on and have the teflon sit right. This requires having the worm gear out of the way, then resetting the worm after the clutch sandwich is together.

I used a good caliper to center the worm and gear off the back mounting plate. I then set the mesh ~just..to..zero~ when I tightened the worm mounting block.
Here's what I thought about. There will be no guarantee that the gear is perfectly round and centered. The contact point I used to set the mesh might be 'in' and another part of the gear might be slightly 'out', this is called runout. If the runout is not more than a few thousandths of an inch (.003") and it is properly lubed, the worm and gear should run right through a tight spot. If the mesh was set to zero at a high spot, then runout would cause a hair of slop at the low spot, but should be trivial and not a 'loose' concern.
i did not check the gear runout proper, with a needle guage on individual teeth. I did check runout with a set marker at zero with a back light, and I did not notice any visual deviation. A back light can easilly illumnate a gap less than .003" so I'm quite satisfied with the factory machining.

Like you, I get way funneled on my work and documentation goes out the window. If I don't funnel, I lose it. Notable attention/memory flaw that I deal with and keeps me from some coherency and follow up in post.
I've completely redone this mount to show condition both cosmetically and mechanically. Link is here:

http://www.cloudynig...4966686/page...

#6 hottr6

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Posted 22 March 2013 - 09:01 AM

Nice restoration. :)

The Meade manual that accompanied the GEM Starfinders advise setting the mesh to zero, and then to back off. I'd say Meade were anticipating non-zero runout on their gear cuts, and heading off any complications at the pass.

Accommodating non-zero runout is SOP for vintage auto gearbox and engine bottom-end builders.






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