Re: Clutch Plug Removal on AP 900
Robert,toggle quoted messageShow quoted text
A good description. You have helped many future plug replacements! Thank you.
From: firstname.lastname@example.org [mailto:email@example.com] On Behalf Of Robert Chozick via groups.io
Sent: Saturday, April 04, 2020 12:19 PM
Subject: [ap-gto] Clutch Plug Removal on AP 900
I just replaced the clutch plugs on my 2010 AP900 mount and wanted to describe my experience and give some pointers to possibly help someone doing it for themselves.
My mount had gotten to the point where my RA axis would barely turn when balancing. Major variations in movement of my counterweights showed no difference in balance. My DEC axis has never been a problem. It has always balanced easily. I decided to go ahead and replace my RA axis clutch plugs.
I ordered the special screwdriver tool and plugs from AP. I got extra plugs for future changes but only needed 4 to just change the 4 RA plugs.
The first one came out like a charm exactly as described. "Great - this will be easy" I said. I just gave 2-3 fairly hard hits with a smaller size hammer and screwed it out. You have to apply a lot of downward pressure as you screw it out but as it gets to the end start applying less pressure or you will have the problems described below. Even if you do apply less pressure at the end you may have the below issues.
The second and fourth one had the same issues. The plug came out fine up to the point it got the the edge of the channel but at that point started going backwards. I let off the pressure but it would only turn in place. I decided that the plug needed to be larger in diameter to be able to screw out. (These plugs are really only the width of between the threads but are larger in diameter only because of expansion from use and the tool going inside to expand them) The plugs have a hole through the middle. I took a screw and turned it about half way through the plug to expand its diameter. I took out the screw and then put the screwdriver tool back in and could turn it a bit more using very slight pressure. I could get it to the point it was about 3-5 mm above the edge and then took a small pliers and turned it for the remaining rotations to get it out. On the fourth one i squeezed a bit too much and almost had to start over but it came out. Be careful how much you squeeze.
The third one was the worst. I had to do the same procedure as I described above for the second and fourth but the plug kept going back in. I reinserted the screwdriver tool a few times and had to whack it with the hammer again. It did finally go above the edge but as I took it out with the pliers half of it crumbled. The remaining stub proved to be enough to grab to unscrew it with the pliers.
Thankfully this procedure worked and all 4 plugs have been replaced. I am glad i did not have to take the axis apart since George’s description of that process sounded awful.
Once you get the old plug out you just drop a new one in and screw the clutch knobs back in. George recommended not putting any oil in so disregard that part of the instructions.
If you have real problems with your clutch plugs it is worth replacing them. My RA axis balances beautifully now. I put a scope on the mount and the axis moved for very slight changes in the counterweight.
If you do not need to replace the clutch plugs I do not recommend doing it just for maintenance purposes.
I decided that when my mount is not in use I will leave the clutch knobs slightly loose so maybe the plugs don’t deform as much over time. I usually leave my mount outside without a scope on it. I just have a pier and a cover so I don't leave scopes or any electronics out. Your situation may not allow doing this.
I hope I can save someone some grief when replacing clutch plugs.