Everyone,

I'm refurbishing an old Sekai 2500 Grandtour, which has its original Suntour Cyclone rear derailleur. It's working well with a lube and new pulleys, but the spring does not seem to be able to move it to the smallest cog any more. Can this spring be replaced, or . . . ?

Thank you . . .

got a Time Machine mr Wells, HG ?

Realistically? just buy a new RD..

... are you sure the high side limit screw was backed out fully?

When you remove the pulley cage, there are multiple slots to put the spring's upper tang into. Move it around a notch.

I doubt it's the spring. Assuming you backed off the high gear limit, it's probably something binding the mechanism someplace. Remove the wheel, and work the derailleur in and out by pushing the bottom assembly, or pulling the cable away from the downtube like a bow string, ane letting it back slowly to see if there are sticky places.

Once you massaged the pantograph a bit it should work fine.

thats chain wrap-up tension rather than lateral stroke , <guess>? he was talking return spring not pulling the full width of the stroke.

i've had older derailleurs with the same problem, could even have been a Cyclone. anything that requires more oomph to return the parallelogram in the DR to a resting position will create a similar result. i've found that due to the lack of use of the smallest cog and consequently the lack of use of a fully collapsed parallelogram that a ridge can develop, due to wear, between the male portion of the parallelogram and the female portion, preventing it from collapsing completely, even if the spring tension id adequate or the the cable runs freely as it should. you might want to take a look at it. it's pretty obvious if it exists.

i remember having to give the RD a light kick with my foot in order to get it to drop into the small cog on occasion until i found the culprit. a little filing did the trick. of course, additional spring tension may remedy the situation, but with consequences that may not be acceptable.

Thank you all very much for the help. I did make sure the stop screw was not the issue. I cleaned the derailleur before reinstalling it, but I'll go back and lube/exercise it again - and also look for those ridges.