Re. cycleman's chain problem - I presume it is dropping onto a higher gear ( cos of chain-line comment and otherwise it'd be a simple case of limit screw). Has it always been a problem or has it only recently manifested? The only alternative to spacing out the cassette that I could think of was possibly a shorter axle BB - more hassle and expense (if possible). Cheapest and easiest solution would be to sacrifice bottom gear and adjust limit screw to make it out of bounds - but presumably the bottom gear is needed.
Combination of issues:
- Cable tension and limit screw in need of adjustment, causing it not to stay in the lowest gear. That was easily resolved with appropriate twiddling.
- When in the (?50T) lowest sprocket and under load, the chain would drop off the *top* of the sprocket (so not derailleur-related) early whenever a shortened-tooth-for-ease-of-shifting reached the 1 o'clock position (so a couple of times per wheel rotation), causing annoying graunching that *feels* like a derailleur adjustment problem, but isn't.
As a work-around, we twiddled the limit screw to make that sprocket out of bounds, losing the bottom gear. The chain behaves fine in the second sprocket.
I wondered if moving a smaller sprocket to behind the cassette would make it work, sacrificing some less useful gear.
(AIUI this is a newish chain and cassette, and the problem was probably introduced by fitting a cassette with a dinner plate for a sprocket.)
((As is common for recumbents, the bottom bracket makes not a jot of difference to the chain-line, as that's determined by the drive-side idler pulley. Which can't move any further inboard on account of the chain having to clear the suspension pivot.))
