I cycle every day because I live in a city and I find it a fun, fit and convenient mode of transport. I am not a cycling hobbyist, am only averagely fit and know pretty much nothing about bike engineering. So every year or so I take my bike in to the shop for servicing.
The bike in question is a Dahon Jack - it's a full-sized frame folding model. So the frame design is a bit unusual. It looks like this:
The last time it was serviced, a couple of weeks ago, the man in the shop drew my attention to a small crack in the frame. It's on the very top bar and has originated in the gap in the frame where the bike folds. Here's a photo:
The two white lines on the tip of the crack are scratches I put there to see if it's getting any bigger. It hasn't in the two weeks since it was discovered.
The guy in the shop said that while any frame crack is serious, this probably wasn't a big deal. Because it's a folding bike, the load is carried on the thick diagonal strut instead of the top bar. So even if that top bar does suddenly split, it's not going to cause the bike to collapse or throw me off.
He advised me not to take it off-road (which I never do anyway) but that otherwise I should be safe to ride for the time being, unless the fracture grew significantly.
Is he right? Should I get this bike replaced right away? If not, how long do you think it might be safe for me to continue to ride, and what warning signs should I look for to say it's no longer safe?