My Curve SL is two years old and has about 2500 miles on it. Best purchase I ever made - it has brought me hours of enjoyment . I use it almost daily - for commuting, multi-mode Japan exploring, and have taken a few longish rides over 50 miles and climbed mountains (well one - twice). I live in a hilly area, so I use every gear of the SA 5 speed hub on nearly every ride. I really like the hub, it has nice range and is relatively light weight. For the first few hundred miles I had to frequently adjust the hub, but since then, It was a pleasure - I very rarely had to adjust it.

A couple weeks ago I bought the bike into a nearby LBS to tighten up chain, as it had a lot of slack and came off a couple times. Since then (about 2 cm of slack now), I have been having lots of trouble with the hub. The best I can do is get it so that I have gears 1 to 4 with 5 not engaging(noisy too - sounds like marbles rattling around a can). The shifter also is different - no more solid click as I change gears. 4th is a quiet click and I push it from 2nd to 1st with no click at all.

Before I bite the bullet and spend a fortune at a folder specialty shop (Loro) in the hope of fixing, anyone have any ideas? Also, I was planning to try to complete a couple stages of this long distance event in October

https://www.tour-de-chiba.jp/

if it turns out that I need a new hub I was wondering what options I have for upgrading this bike for long distance rides - without adding too much weight?

All your symptoms sound like a badly adjusted cable and not deterioration of the internals of the hub (although they will fail if you ride around with a badly adjusted cable).

It is very important to follow the instructions for cable adjustment on in gear hubs. If you don't have a manual for the adjustment this download from Sturmey-Archer contains the info you need. It is for a hub with an internal brake, but the gear adjustment should be the same.

Many people think you can adjust a geared hub just like a derailleur, ie just twiddle the adjustment until it sounds ok. This is perfectly ok for a derailleur, but it is really bad for the geared hub which is dependent on several critical parts being correctly aligned internally, and this can only be achieved by following correct adjustment procedure.

Often young staff in bike shops are the worst offenders because they have no knowledge of hub gears.

Once the hub is correctly adjusted it will stay that way unless the cable is disturbed (eg remove back wheel) or if the cable "stretches" (after installation of new cable)

Thanks Datako. I think cable tension was too great after the LBS kid(how'd you know?) pulled back wheel (too much?) to remove chain slack and then adjusted gears without knowing what the shifting should feel like. 5th gear is now back and shifting feels better after a short ride, but still not perfect (still no click downshifting 2nd to 1st), but hopefully just a bit more fiddling will do it. I had to move the cable adjuster and the cable connector a lot to create enough slack in cable to improve the shifting and then centered the blue line to end of axle.

Moral of story - take the folder only to a shop that knows folders(and IGH's).