On my 1977 Centurion Pro Tour I have a Suntour Cyclone GT tied to a Suntour Barcon.

Sometimes in the low gears the chain will jump to the inside of the guide pulley, lodging against the cage of the derailleur, usually pulling the chain between the freewheel and the spokes. The teeth on the pulley look slightly worn, but not overly so.

Does anyone have any insights into what might cause this? It happened twice when I first got the bike a year ago, and then three times yesterday on my way to work. Then I got a puncture at midnight on my way home...

I'm thinking about disassembling, cleaning and lubing all the pivots again to make sure the springs are snapping it back into place quickly.

I have seen this happen on old good dérailleurs using newer thinner chains - Worn pulleys also contribute and until you get out the old caliper you really cannot see just how much of the pulley is worn down - Get a new set of pulleys and put them on top of the old ones to check for wear - You may be surprised...

+1 my lower pulley had huge gouges worn into the tops of the teeth. When I replaced it this problem was greatly reduced, though it still occurs a little bit. I suspect my narrow 8-speed chain, since it doesn't have the protruding rivet heads on each link plate. (This is with a Cyclone Mk II GT rear mech, 7-speed Hyperglide cassette hub, and KMC X 8-speed chain.)

Thanks. I had figured it was probably the pulleys. Time to go to the LBS!

This is so strange, I currently have 3 bikes with Cyclone GT Derailleurs and the one on my Centurion Pro Tour is the only one i've ever really had any trouble with and I'm having the EXACT same problem.

Mine never jammed or anything, it just made an annoying sound.

Talk about timing!

Oddly enough, this is the same problem I've been having with a 600 derailleur. This afternoon I put 'er up on the stand and took a close look at the idler pulley wheel and watched closely as I ran through the gears. I noticed that the chain acted "jumpy" at one spot on the idler pulley wheel: sure enough, one of the teeth was really worn down. I ran down to the LBS; he had a pulley wheel that he just gave me (great guys!) Ten minutes later I had the new one on, the old one in a recycle box, and the chain was running smoothly. I went out and rode a quick eighteen miles with nary an errant noise from the rear!

I bought a set of Shimano pulleys with bushings. I haven't had a chance to install them yet, but I'll do it tomorrow. I'll report back with results.

So, the inside diameter of the modern shimano bushings is too small to fit over the shafts of the Suntour derailleur.

Is my only option really only a set of $$$ vintage Bullseye pulleys? I don't want to try to machine down the diameter on these aluminum shafts.

Buy an old Suntour derailleur with good wheels and swap them out. Any suntour fits any suntour.

For the extra $20-30, I might just get the bullseyes.

Bullseyes are pretty and last a long time. I never believed in the "performance" but they are gorgeous.

I might be mistaken, but don't NR wheels work on SunTour and vice-versa?

I guess so, I succesfully intherchanged between Suntour, Shimano and old campy (I'm ashamed to say that I rode around for a while with a super record derailleur rocking Shimano 60 jockey wheels )

For the curious, I tried the following with poor success:

Modern shimano jockey wheels with bushings. Internal diameter of the bushing was too small for the shafts on the Suntour Derailleur.
V.O. Grand Cru cartridge bearing pulleys. Look suspiciously like the ~ 2x more expensive ones from Origin8. The 11 tooth pulleys are too big to fit into the cage of the derailleur. They hit the pins that go between the sides of the cage. This is really my fault, because I didn't read too much, but calling it a "universal" pulley and insinuating that it works with most vintage derailleurs is kind of bogus when they won't work with what's arguably the best brand of the period. I'd have gone with 9 or 10 teeth, personally. It's a shame, though, because the inserts and bearings work really well.

So I bought a Vx short cage derailleur for a few bucks at the local Coop and the derailleur looks rough, but the pulleys look mint. Should work just fine. After I clean up the body of the derailleur, I can probably sell it for more than I paid sans pulleys.

Flats at midnight? Get a shaman or a priest to banish the evil spirits.

We haven't retaliated for some nonsense by exporting the goathead thorn to Mexico yet? ;-)