Beyond all of the things which aren't technically correct with my particular set-up, I have a couple simple questions relating to derailleur function only. The first is this: Suntour Cyclone & Cyclone GT Cages c.1980 In the top view, what is the purpose of screw # 23? I came around to this in trying to figure out why the derailleur itself is making so much noise--seems unrelated to the obvious chain issues. I could be wrong, of course. In my case it's a Suntour VX, but the screw in question is the same.
Thanks

It appears to be the cage stop; it is used to keep the cage spring under tension.

I believe its only function is to act as a stop for the cage plates.

that's the one you unscrew first when overhauling any derailleur to remove all cage spring tension.

it's always a pain for me to reinstall it. a magnetic screwdriver helps a lot.

i didn't know it was removable the first time i ever overhauled my first derailleur, a campy nr one. i tried everything i knew to return tension to the spring with that stop screw still in place. it's essentially impossible, even using a vise and pliers. several bloody thumbs later, i turned to the advice of bike forums.

Yes, but the derailleur comes apart without removing the stop doesn't it? Even though I knew about removable stop I had one in a Nuevo Record that was stuck, so I tried for about an hour to install the cage. Finally I made a tool where I could use more force than a screw driver and it worked.

^ to fully overhaul any derailleur of this vintage type, you first remove the stop screw.

if you try to separate the pully cage from the body without first removing the stop screw (which will then allow the release of pully spring tension), the spring will snap, and you may not later know the exact notch the spring was in originally (if there are more than one). it's nearly impossible to recharge the pully spring and reassemble the derailleur with the stop screw in place. it's the first to unscrew on disassembly and the last to rescrew on assembly.

a pully spring snapping your thumb in surprise attack is not fun.

I agree. The last thing you do is rotate the cage by hand and re-install this stop-screw to return the cage to tension. The tuning of the tension comes from selecting the notch where Spring 20 fits into Shaft 21.

The whole system is a massive pain on the GT derailleurs where Shaft 21 is also the pivot for the guide pulley.

+1 to all above. Another q: if using one of these without the deraiileur hanger do you still attach nut #6 to the derailler mount bolt?

^^ I read somewhere that you do; I unfortunately don't have one easily at hand.

No. If your frame is equipped with a Campagnolo-style integrated derailleur hanger, then it is the threaded piece that replaces that nut. Assuming your mount is a threaded Campagnolo style, that is.

OK, I'll buy that. The reason I asked is b/c at first glance it seemed like that the mount bolt might be too long without that nut for a threaded dropout.

Another thing to note about the VX rd: on mine the jockeys (including the dust caps) are specific to their position (guide or pulley). If you mix 'em up they may not turn smoothly.

Not to highjack, but one more q: I'm in need of a barrel adjuster for my VX. But it seems that it uses a smaller diameter than a "normal" size brake adjuster. Does anyone know if this size adjuster is commonly available?

Hijack away

great point. and i wish i had read your post a month ago. i overhauled one, mixed up the wheels, and on reassemly, one of them wouldn't turn. took way too long to figure out what happened. i had never run into that particular quirk before with an rd.

i'm having a problem getting my v-series to swing freely in the on-frame hanger with the hanger bolt tightened down.

if any of you have any quick tips ...

im glad to know that I'm not the only one who's done this. I figured it out after a couple of frustrating hours... this morning.