Is there a way to prevent chains comming off often?

[MontyVeda]

I can't remember the last time the chain came off... that to me is like white dog poo and platform shoes. Your gear stops need fettling.

 

[slowmotion]

Having offered advice to @Randombiker9, I went out for an hour and half 's bimble around west London. Half way across Talgarth Road, with two lanes of impatient traffic behind me, the chain dropped off the smallest rear cog and jammed against the frame, leaving me motionless in the middle of a six lane junction, pedals totally redundant. Serves me right.

 

[Profpointy]

Randombiker9: if you are serious about solving the problem yourself, my advice is to buy a cheap repair stand. Without such an investment, indexing and setting limit screws is a nightmare. A stand will pay for itself almost immediately. The best and most comprehensive YouTube videos on this subject are produced by Park Tools. Most others seem to overlook key areas.

Whilst not denying such a thing might be handy for some jobs I've not needed one in 40 odd years for merely indexing the gears. Just turn the bike upside down !

 

[Profpointy]

If the chain is coming off the back, walk it to a bike shop and get it sorted. It could (jam the wheel/tear through your spokes) and have you flying over the handlebars.

If it's the front, yeah, you can probably fix it yourself. Certainly worth a try.

At the risk of being pedantic, you'll jam the back wheel not the front in the worst case scenario you mention. You won't go over the handlebars. Granted you may fall off.

 

[Randombiker9]

Does the chain come off at the front to the outside of the large chainring (ie towards the crank) or to the inside and gets stuck between the seat tube and the inner chainring, or both?
Does the chain come off at the rear to the outside of the smallest sprocket (cog) (ie towards the dropout) or to the inside and gets stuck between the spokes and the largest sprocket, or both?
When the front derailleur is pushed across to shift onto the large chainring, how many millimetres are there between the cage and the chainring teeth (ie how many mm would you have to drop the front derailleur to cause interference)?
https://www.parktool.com/blog/repair-help/front-derailleur-adjustment
https://www.parktool.com/blog/repair-help/rear-derailleur-adjustment
Patience is required.

Thanks and it just comes off the front/outside of the large chain ring.

 

[Tim Hall]

Thanks and it just comes off the front/outside of the large chain ring.

Bonus question: Does this happen when operating the front or rear changer?

 

[Ajax Bay]

it just comes off the front/outside of the large chain ring

There are two screw heads on the top of the shifter mechanism. Screw the outer one in, half a turn at a time, ride the bike and test, and repeat, until the chain won't shift into the large chainring. Unscrew half a turn and test. Good chance it'll be OK (and the chain will not come off in the way you have experienced).
Having suggested all that, I reiterate several other posters' (above) suggestion that you learn to index your gears. It is not easy but once you get it right you can cycle with gears that change efficiently as designed. Gears that skip or (worse) where the chain occasionally comes off are an unnecessary and avoidable hassle.

 

[Randombiker9]

There are two screw heads on the top of the shifter mechanism. Screw the outer one in, half a turn at a time, ride the bike and test, and repeat, until the chain won't shift into the large chainring. Unscrew half a turn and test. Good chance it'll be OK (and the chain will not come off in the way you have experienced).
Having suggested all that, I reiterate several other posters' (above) suggestion that you learn to index your gears. It is not easy but once you get it right you can cycle with gears that change efficiently as designed. Gears that skip or (worse) where the chain occasionally comes off are an unnecessary and avoidable hassle.

Thanks