Chain coming off help please

[wisdom]

In all my years of cyclingI've never failed to solve a problem (without this excellent site of course).This one is baffling though.
I have finished restoring a dawes fleur 5 speed non indexed racer for my Daughter.
Its only done around 1100 miles from new but has been unused for many years. Everything is at it should be (I think).It kept unshipping the chain from the top of the front sprocket in bottom gear.So I have put on a new chain as the original was tight and the wheel was only just in the dropouts.
This is now what I consider the correct length with nice tension and no sagging. It runs nicely throughout the gears smoothly, but its again unshipping the front sprocket as before. Where do I go from here as everything appears lined up correctly ?
Forgot to mention new inner and outer cable fitted if it could be relevant

 

[Koga]

I am sure you did, but have you checked the bottom bracket bearing ?

 

[wisdom]

Thanks for the fast response.
The bottom bracket was stripped, cleaned,regreased and re assembled. There is no play and it turns smoothly.

 

[Crankarm]

Sorry what does UNSHIPPING mean?

 

[wisdom]

Sorry coming off.

 

[Koga]

Thanks for the fast response.
The bottom bracket was stripped, cleaned,regreased and re assembled. There is no play and it turns smoothly.

Which side is it coming off, pedal side or bike side ?

 

[RecordAceFromNew]

There can be various reasons.

If it is truly a 5 speed (i.e. only one ring up front) it is possible that you have flipped the bb spindle during its service and it is an asymmetric square tapered, so you might want to check the chainline (i.e. distance between centre of frame and middle of front ring). For a 5 speed with rear dropout distance of 120mm it should be around 43mm.

If it has a front mech then the limit screws or cable tension might be out. This is an excellent guide.

Other possible reasons include stiff/bent links in the chain or bent chainring etc.

 

[wisdom]

In reply
The chain is coming off on the bike side.

Its a true 5 speed with cotter pin cranks

 

[Brommyboy]

Put the chain on the largest sprocket and tension it: there should only be 2 extra overlap links. Any more and the chain will come off when using the smallest sprocket.

 

[Cyclopathic]

Perhaps a different make of chain could help. Is it possible the existing one is not flexible enough to cover the range of gears?

 

[wisdom]

Its a brand new chain as it was doing it with the original chain.

Its fine on the small sprocket at the back its coming off the front sprocket when its on the bottom gear at the back

 

[mrandmrspoves]

My best guess would be chain line as already suggested - either because you reversed an asymetric crank spindle or because the rear wheel is not correctly situated with washers in the right places. Another thing to check for is the teeth on the front chainring - is one of them damaged or bent?

 

[Gravity Aided]

I would have to agree with the above, although it may also be the whole chainring that is bent to some extent, if you unship the chainring and place it on a piece of glass, using it like a surface plate, you will soon find the culprit.

 

[Nigelnaturist]

Whats wrong with "take off" or "coming off" as opposed to unship/ing which sounds like your unloading a ship.

 

[wisdom]

Apologies.
Nautical background you see.