My neighbor has a Camping World 'Adventurer' folding trike (not allowed to post a link but it's on the Camping World website) with a 3 speed 'Sturmey Archer' branded gear-set and coaster hub brake. It's a nice unit!

Its longer chain runs over a simple tensioner that has no adjustment left - the chain desperately needs replacing although the chainwheel and back sprocket don't look badly worn. I maintain her trike when I'm in the US but right now I'm not so she's had to take her trike to the local bike shop for puncture repairs and servicing. The local bike dealer didn't replace the chain and appears unwilling to tackle what I see as a simple job. When I get back I want to source a replacement chain because the nearest boxed one in the shop is one link shorter than needed - I counted the links on old one to check.

I'm 71 and learned my bike stuff quite some years ago but can't figure why bulk, loose chain can't be 'cut' (split) to yield the correct number of links. But the bike dealer seemed unprepared to do that and I'm left wondering if there's something I don't know.

Are chain link dimensions 'universal'? ie Is the link size of the Chinese original the same as replacement chains for sale in the USA? Will a new 73 link chain be the same length as the original 73 link one used to be when new? Can she order one that's the correct length or will she have to order a longer one for me to split?

Sorry if that's a really basic question but I don't want to waste someone else's money.

Yes they are still the same one inch pitch if that is what you are asking. Chances are it is 1/8" which are pretty common.

a bike shop can shorten the chain and put it on .. they do not come pre made to your needed length..

AW3 cogs are made in 1/8" & 3/32".. thickness from 13 to 21 teeth ..
the 16t + are dished/offset, 13-15 are flat.
they are low cost, (interchangeably, Shimano 3 speeds use the same cogs)




..

I was under the impression that pitch is usually ½".

What I did wonder, though, was whether foreign chains might be closer to whole millimetre values than they are to whole to imperial ones. If they were then a half inch pitch chain might not properly fit metric sprocket cut-outs - if such things exist.

I haven't been able to understand why a bike shop would balk at replacing the chain unless they can't be bothered to obtain a longer-than-standard chain that would need to be shortened to fit.

I could shorten a longer-than-standard chain myself but if I can order one with just a single extra link it would avoid effort and surplus chain wastage. As I suggested, the bike shop seemed unwilling to do this. I wanted to be sure there is only one pitch for all simple-bike chains. I don't know what profile the sprockets are but I'd guess they'll be bog-standard for a cheap bikes. If I end up having to do this work myself I'll measure the present chain's width and get the new one one to match.

The bike shop ought to have dealt with all this when asked to!

A quick look on Nashbar's website shows two single speed (1/8") replacement chains, one wih 112 links, the other with 114 links. Either should work on the trike. Chain tools can be found on many multi-tools or as single purpose tools. Breaking a chain takes about a minute or less with the right tool.

Sounds like you need to go to a different bike shop or get the tool and do it yourself.

Yeah I used a (borrowed) rivet extractor after I removed the current, old one to check how many links it has. Then I re-fitted and joined it with a quick spring-link. (is that the right term?) I used to have chain tools for my motor bike with one to draw together and hold the loose chain ends to fit the joining link. But that was 50 years ago and I doubt that I can find those ancient - but still relevant - tools now! Thanks for looking up the two lengths of chain - it shows I wasn't far off the mark in what I'd surmised about getting long chain lengths. I might see if I can get one twice the length needed and make a couple of chains Probably simpler to buy two standard, long ones I now think so I can clean and lubricate one properly while using the other. That might help increase their lives in the Sonoran desert dust.

My view is that the bike shop guy is both a lazy arse and has too much business and too little competition. No wonder folk go online when you get crap local service - the USA surely didn't use to be that way - or did it?

Thanks for your help!