Hello everyone.

I own a bickerton 1909 junction seen here (can't post links)
however the pedal snapped off very early and after waiting weeks for a replacement part, Halfords without asking replaced the custom FSA vero 55 t chain set with this one (f gimondi 130mm crankset) which I didn't think looked as good as the original nor wanted for warranty reasons however I needed the bike to travel to work so took it home.

Since then I have had to change gears individually in order to prevent the chain from falling off. This never happened with the original crank/chain set (I apologise for not being 100% on the terminology) but I was able to use the bike. After a year the chain snapped and was replaced and since then I cannot go into top gear (9th) without the chain slipping and falling off. If I try to pedal fast or put any strain on the chain it also 'slips' and falls off, as it does if I go into the upper gears (1-3).

I took the bike to a repair shop who advised that due to wear and tear a new chain set would be needed. I can take photos if necessary as it doesn't look worn at all. The original shimano cassette would need to be replaced also as it is worn. I understand the cassette needing changed however the crank set does not seem worn however I have started searching for alternatives to fix the issue.

My problem is when search for a 55t fsa vero chain set I am unable to find any. Would 54t or lower suffice? I would like the chain to be as tight as it was originally and if I have to pay £100 or so I would rather have the original chainset put on it, but I cannot find it anywhere. I have found an outer ring that would suit but it does not have a crank arm or inner ring, I don't know what to search for to complete this or even if having an outer ring alone will suffice.

Does anyone have any ideas? What do I need to search for to complete the outer ring? Does 1 year seem short for a £100 chain ring to be worn out? Can I search for something with 54t as an alternative? Should I try and change the cassette before the chainset to see if that resolves the issue?

Any advice or tips people may have would be much appreciated. I am new to this forum and will post this under general discussion to get as much opinions as possible. Thanks for reading.

Sounds like the onus lies with Halford's to make it right. They've swapped out a part without consulting you, which is not performing as well as the one it replaced. Although swapping out cranksets shouldn't present any problems as long as it is equivalent in all measurements (chainline, tooth width, ring size, etc), it does sound like they either swapped in something that isn't compatible or they swapped in something and never made the adjustments to keep things running smoothly. Either way, that would be my first stop.

Did you contact Mark from Bickerton ? Good bloke and eager to help. I ampretty sure that the chainring on your bike was one of the high quality ones like Tern is using in their top models. They prevent chain dropping and somehow been able to guide the chain better than low end chainrings
go and ask Mr Bickerton and he will know

The chain guards often seen on 20 inch bikes not only can keep your pants out of the chain ring but can prevent the chain from coming off the chain ring. My Swift was pitching chains, particularly when peddling fast and going over bumps when I used a chain ring with out a guard. Restoring the guard solved the issue. I have had good luck with Vuelta chain rings which come in a range of sizes, both teethwise and BCD.

I wonder if the bike shop who replaced the pedal actually stripped or cross-threaded the original crank arm thread, wrecking it. Unfortunately it is now a year or more on and no way to go back. But you definitely need a chain guard on the outside to prevent chain drop. Another possibility is to mount a cheap front derailer on a suitable clamp for Tern bikes, which do exist.