Chain just coming off

[Joe24]

On the fixed today, my chain came off twice, before i left the group and limped home.
The first time i could sort of understand. I was going down a steep-ish hill, spinning fast that was a tad bumpy, so im guessing on a slack spot the chain came off. It was ok, came off front and back and my back wheel didnt lock up.
Second time, just gone over the top of a rise, on the way down the other side coming up to a RAB the chain just jumped off again. It was on tight enough so it wasnt that, and the chainring is not bent.
So i have no idea why it came off. The fixed is now lighter, and looks like this.

Im getting a new fixed frame soon, and putting some of the stuff from this fixed onto the new frame, with some new nice parts
Then the old fixed frame will be turned into a TT bike when i have enough money.

What makes my chain jump off? Was i lucky that it didnt catch?

 

[spandex]

It is good to know that you are ok

Why
chain line
slack chain

 

[peejay78]

what he said. ^

 

[Joe24]

It is good to know that you are ok

Why
chain line
slack chain

Chain not that slack. It does go tight/slack but in the slack bit it wasnt that slack. Its been slacker
Cant do much more on chainline, cranks over as far and chainring on other side of the spider.
What are the chances for the back wheel to lock up? Is it a larger chance or just 50/50?

 

[peanut]

were you in or out of the saddle at the time ? just thinking it must be due to misalignment between the front chainring and the rear sprocket. Have you checked from the rear? maybe put the bike on a stand and turn pedals backwards as well as forwards and see how true the chain runs

 

[Joe24]

were you in or out of the saddle at the time ? just thinking it must be due to misalignment between the front chainring and the rear sprocket. Have you checked from the rear? maybe put the bike on a stand and turn pedals backwards as well as forwards and see how true the chain runs

Sitting down both times.
Cant put it on now, everything is off it.
Just seemed strange that it just popped off, even after i had put more tension on the chain.

 

[spandex]

It is the chain line mate going by what you have said. The only way to move it over is to get a shorter BB.


You asked what is the % of the back wheel locking if the chain came off? Now one can say for sure but it will be Hi I would of thought?

 

[spandex]

And just remember what happened to me when I came of my fixed at speed.......

 

[Joe24]

And just remember what happened to me when I came of my fixed at speed.......

I do, it was very scary when the chain came off the first time, i was doing about 30mph

 

[Dave5N]

Is the chain or transmission worn?

 

[Joe24]

Is the chain or transmission worn?

Chain was new just before xmas. Chainring new jus before xmas. Sprocket is an old one, it isnt worn though.

 

[spandex]

Chain was new just before xmas. Chainring new jus before xmas. Sprocket is an old one, it isnt worn though.

My chain was new 8months ago and it has done say 1500miles KMC Z610HX with a tensile strength of 1,500 Kg and mine is dead that is I need a new one now dead.

 

[peanut]

Sitting down both times.
Cant put it on now, everything is off it.
Just seemed strange that it just popped off, even after i had put more tension on the chain.

It could have been due to the bottom bracket moving sideways under pedalling pressure . Old steel frames deflect a lot around the BB especially if they are big frames like yours

 

[Joe24]

My 1/8th has only done about400/500miles since it was put on. Not done much.
I am getting a new one for when the proper fixed is built up though.
The other 1/8th chain i did about 1500miles on hadnt worn much, but i had twisted 2 links in it so had to get a new one. Thats the power for you

 

[Joe24]

It could have been due to the bottom bracket moving sideways under pedalling pressure . Old steel frames deflect a lot around the BB especially if they are big frames like yours

Does that mean that the bottom bracket moves from side to side?
If so, thats what ive been told as to why the chainring collapsed, but was said the frame flexed, now that the BB was deflecting.