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Re: GM8 Bore Trueing & Bearing Replacement

 

Eric,

Thank you for that detailed description. ??

The root cause seems from your writeup to be incomplete (tilted) bearing seating into the (correctly) machined sleeve.? So your tool kit and some rubber mallet blows are the solution....if owners feel that binding.

We do not know if the original condition had the bearing seated on a tilted sleeve, because L. re-machined that.? Did they say what they found?

I always thought that binding was primarily caused by the worm to ring gear spacing. I think your analysis say that, in the case of new or used mounts, we first remove the worm assembly and just feel for bearing smoothness first. If that is sticking, it must be fixed before the worm is installed. ?

Do I have this right?

Best,
Michael?



On Sep 13, 2017 12:54, "echesak@... [Losmandy_users]" <Losmandy_users@...> wrote:
?

A short review:

I bought a really pristine GM8.? But when it arrived, the DEC axis was stiff and binding.? Upon disassembly, I found that the DEC shaft had some significant wear marks, indicating that the bearings were not riding true on the shaft.? I initially thought it was a problem with the bearings.? I didn't have the time to do the work to replace them, so I shipped the DEC bore and shaft to Losmandy for repair.? The DEC shaft was replaced and the axis returned.? But when I reassembled everything, the binding was still evident.? So per Scott's request, I this time shipped then entire DEC assembly to Losmandy. The DEC axis was returned to me 4 weeks later with the same binding, plus a little new shipping damage.? I was quite disappointed.

After 2 trips and 6 weeks, it was clear that I was going to need to get this working myself. I wanted to replace the bearings.? So I machined some tooling to remove them.? Upon doing this, I found that the upper bearing housing was not pressed into the DEC axis bore completely straight.? I used feeler gauges to measure the difference in gap around the circumference of the gap. It clearly doesn't take much misalignment to cause the binding, as I was measuring a difference of about 0.006".? I corrected this misalignment with a series of appropriately placed hammer blows and a wood block (with the bottom of the DEC axis sitting on protective material).? I was able to correct the misalignment to within 0.001" (one thousandth).?

I then installed new bearings in the bore and tested the axis for binding.? It was silky smooth with no binding.? It's actually one of the smoothest Losmandy mounts I've owned.? I'm now wondering if some of my other mounts had a similar problem.?

I uploaded a couple photos and some further instructions.? I'll also loan out the bearing tools, should anyone want to use them (contact me for details on my website).? Here's the link: ?



Thanks to those that responded to my earlier posts.? I hope this is a help to others having similar issues or looking for a bearing replacement.

Best,?

Eric
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