I had to replace all the clutch plugs on my AP-900 and it was a bear of a task, almost unbearable, even with AP’s special plug removal tool. It was only possible thanks to George and his marvellous advice, on the easy and smart way of using a 3 or 4 inch long (socket head) as a “push screw” and my socket wrench, to pull the axle head off and disassemble the axes. Then it was easy to remove the badly deformed old plugs.
As usually happens, the DELRIN plugs aged and flattened out at their tips (from a few years of being tightened down too hard), becoming mushroom-shaped, and had spread out between the bottom of the clutch screw hole, and the clutch axle itself. There was no way it was ever going to be extracted, up the clutch hole, no matter how good the tool. The mount axes had to be disassembled.
Thanks to George’s instructions on how they do it, the task was almost a breeze after that. Once the “push-screws” easily did their job, I drilled out a larger centre hole down the old plugs, and tapped some looser ones into the now empty clutch channel. I think later, for some of them, I threaded the drilled plug – only half way in, to produce a “tapered threaded” hole. That way, the tap then had enough grip to then push & screw the old plug, down into the channel without much force.
A little WD-40 may have helped loosen it from the hole threads.
The old clutch plugs not only formed mushroom heads in the channel, they also thickened and embedded themselves into the hole threads.
With the axles disassembled, the mushroomed head did not need to force its way upward, but be screwed inward, for extraction.
However, the next time I have to do it – and I really hope there will never be one – I think I might substitute the AP clutch plugs with one’s I found on the web, in CHINA. Or, I will modify the standard AP plug kit.
Those are almost the same, except they are “rounded, bullet-shaped”, at the tips. I figure that their narrowed tips, rather than AP’s straight cylindrical plugs, will not mushroom as much into the empty channel space, beyond the diameter of the clutch screw hole, making extraction much easier the normal way using the AP tool.
Alternatively, I might put each new AP standard kit plug in a drill or lathe, and “round-off” the tips to likewise become bullet-shaped. That would probably be easier than sourcing from China, where they might become unavailable over time, and possibly not precisely the same size. If rounding-off would work, I would much prefer to trust the ones from AP, and modify them.
Also, if those Chinese substitutes are used, you should still source the regular AP clutch plugs to perhaps replace the “bearings” on both axes. The same AP clutch plugs are used as “rollers” in the race channel – i.e. there are not typical “steel ball-bearings”. You will need a KIT of each, plus spares, since you will likely drop and lose some during assembly - about 24 on one and maybe 22 in the other (?) axle. The DELRIN axle bearing rollers may flatten out over time, just like the clutches, perhaps shatter with age and stress. Eventually will need replacement as well, although that has never been mentioned here, or even written about in any AP documents.
The mount really was a joy to use again, after its clutch rejuvenation, and I didn’t need to replace the ones in the bearing race yet, since I am the original owner. But I suppose, under more frequent use and heavier loading than mine, the axes may get “bumpy”, when one or more DELRIN plug rollers chip or shatter, causing a log jam in the race channel. So, keep that in mind.
Here is a link, to the Chinese company – to see what those look like.
Actually, it would be nice if AP could be the source of both the regular clutch plugs for the bearings, and bullet-nosed ones for the clutch holes. The “rounded section” should be slightly longer than the channel depth, to prevent even those from mushrooming and getting stuck.