Changing RA belt on an EQ6 - do I need to dismantle the entire mount?

[Giles_B]

I bought an old (black livery, upgraded to go-to) Skywatcher EQ6 second hand last year - it's been well looked after (well maintained in the past and stored indoors in a dry environment since) and has performed well for eight months, but the RA has stopped tracking well for the last few sessions (the Dec still tracks beautifully) - regularly oscillating several arcseconds positive or negative from the target and never staying any closer for long, despite ramping up the RA guide aggression to 100%. It will no longer handle the 300s subs I have been accustomed to, showing star trails in anything over 60s.

After a frustrating evening confirming the RA is well balanced and playing with the tracking settings, my suspicion has fallen on the RA belt - I wonder if it may have a problem and needs changing. Certyainly I need to open the thing up and see what is going on. This is all new to me and the first time I will be dismantling the mount. It has had a Rowan belt mod so I have followed some videos showing what is involved and I'm just wondering if I need to go through the entire complex process of taking apart the mount I see in the videos just to change the belts, or if there is a way to do this that is a bit less involved?

[1parsec]

Hello,
It will be necessary to take the mount apart to change a belt.
The essential first step is to remove the motors from their mounting plates before separating the mount otherwise you'll damage / break a potentially good belt.
When the motor is removed you will be able to see a portion of the belt through the slotted hole in the axis casting.
The usual cause of the belts being damaged is due to over tensioning.
ATB

[wimvb]

5 hours ago, 1parsec said:

The usual cause of the belts being damaged is due to over tensioning.

That can even cause the motor shaft to snap. It doesn't even have to be excessively over tightened. Temperature cycling and time can cause metal fatigue.

 

[bosun21]

Depending where the previous owner sourced the parts to carry out the upgrade to go to, or whether he bought the designated upgrade kit new. A lot of the cheaper belts can be prone to stretching easily which can cause tiny amounts of slippage. I am not familiar with the older style EQ6 but some degree of disassembly will be necessary.

Edited August 6 by bosun21

[Clarkey]

Personally, I would dismantle and change all the bearings and the belts. Yes it would be a couple of hours work, but having changed the bearings and regreased both my HEQ5 and AZ-EQ6 the effort is worthwhile. As long as you have a modicum of DIY ability, it is perfectly doable. Just follow a decent video and it is pretty simple.

[Giles_B]

Thank-you for all these. Since posting I did a good deal of research and this helpfully confirms what I found and also adds some useful info.

As it was I found once I had worked out what was going on that I was able to tune the mount and restore the great guiding I was getting before - in other words, it was a backlash issue, and it was really the suddenness and severe effect when it appeared that took me by surprise and - coupled with my complete ignorance of how the mount worked - made me look for something catastrophic.

I am glad I got things working again so easily, although I realise I will at some stage have to strip the mount down - the previous owner stripped and regreased it a couple of years ago, so this should be a job that can wait until next year, because I'm not really relishing it!

[wimvb]

42 minutes ago, Giles_B said:

I will at some stage have to strip the mount down - the previous owner stripped and regreased it a couple of years ago, so this should be a job that can wait until next year, because I'm not really relishing it!

”If it ain’t broke, don’t try to fix it.” As long as guiding is good, there’s really no need to strip the mount.

[Giles_B]

@wimvb That's exactly why I am so glad not to be doing the job yet - my waking nightmare was that I would strip the mount and it would guide worse than before, not better.

However I do understand that the grease in the mount eventually pools, so the job needs doing regularly. I imagine there is a sweet spot where this should be done when the guiding is subpar but not a drastic problem - i.e. servicing too late will mean the mount runs dry and the components are degraded. But too soon it exposes the mount to risks from disassembly (primarily dissembling/reassembling incompetently).

As with so many things it is always too soon to intervene, until it is suddenly too late!

[Stuart1971]

6 minutes ago, Giles_B said:

@wimvb That's exactly why I am so glad not to be doing the job yet - my waking nightmare was that I would strip the mount and it would guide worse than before, not better.

However I do understand that the grease in the mount eventually pools, so the job needs doing regularly. I imagine there is a sweet spot where this should be done when the guiding is subpar but not a drastic problem - i.e. servicing too late will mean the mount runs dry and the components are degraded. But too soon it exposes the mount to risks from disassembly (primarily dissembling/reassembling incompetently).

As with so many things it is always too soon to intervene, until it is suddenly too late!

So many people strip there mounts down change all the bearings and so fourth to get maybe .2 RMS increase in the guiding, it’s really not worth it.

Depending on what scope you are going to use and your imaging pixel scale and also the quality of your skies, then you will not benefit at all from the mod, if your skies don’t allow any better than maybe at best 1”/pixel seeing then no point in having the guiding much lower than that, most of the UK you will probably me more like 1.5”/pixel at best with seeing, so guiding at 1.0 RMS is more than good enough, so think about what you are going to use on the mount, and if it’s really worth the time and money…try the mount out first and see how it does as is…👍🏻