Bicycle Mechanics - Chain blows off chain ring

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.



PDA

View Full Version : Chain blows off chain ring

LgReno
07-23-09, 01:53 PM
Hey,

I'm frustrated with my nishiki landau circa 1975-77.

When i pedal off the saddle and press down hard on the crank the chain flies off the large chain ring. makes for an increadibly loud sound and embarassing moment putting it back on.

I've since adusted the fd properly. sill happens. The big chain ring doesnt seem to be more worn than the little chain ring although there is some sign of wear.

The most important observation is that when around the chain rings, the chain can be pushed down further onto the ring than when it rests. In other words, the chain is not flush against the teeth of the chain ring - i can push it down a couple of mm. I dont think this is normal compared to all other bikes in the garage.

where does the problem lie? is it the chain ring that needs to be replaced... or do i need a new chain (possibly streched?)


thanks for helping out,


reno

Al1943
07-23-09, 02:01 PM
You need to measure your chain often. A 24 pin interval of new chain measures exactly 12 inches. By the time any 24 pin interval measures 12 1/16 inches the chain should be replaced. If a 24 pin interval has stretched to 12 1/8 inches or more the cassette or freewheel has probably worn excessively and will need to be replaced.
It's also possible that the chainring(s) have been worn out but they normally last much longer than cassette cogs or chains.

Al
LgReno
07-23-09, 02:11 PM
im gonna measure right now and report back asap

Al1943
07-23-09, 02:15 PM
Also check the frame out closely in the bottom bracket area for possible cracks, especially in the chainstays. A cracked frame could account for throwing the chain under pressure.
LgReno
07-23-09, 02:19 PM
measured center of pin to center of pin i get less then 12 inches (repeated 3 times). a bit confusing.
clancy98
07-23-09, 02:52 PM
are you sure your chain is the right width? not too narrow?
Al1943
07-23-09, 03:18 PM
measured center of pin to center of pin i get less then 12 inches (repeated 3 times). a bit confusing.
You're not measuring 24 pins. Not possible to get less than 12 inches. Use a good steel ruler.

Al
LgReno
07-23-09, 08:58 PM
Ok.. so i went to my schools bike collective where i volunteer. theres a chain length measureing tool. Turns out the chain was very streched. i put on a new one. and not the chain is flush against the teeth of the big chain ring.

BUT!!!... now.. the chain seems to skip in the back... while on the smalled cog. The cassette doesn't look worn at all.

I realize that its best to change threaded freewheel at the same time as a chain... but this is pretty vintage so.....is that the way i should go?

I rode the bike home tonight 35km. Is it too late to add a new freewheel?
let it be know... thats guys!
Al1943
07-23-09, 09:09 PM
Ok.. so i went to my schools bike collective where i volunteer. theres a chain length measureing tool. Turns out the chain was very streched. i put on a new one. and not the chain is flush against the teeth of the big chain ring.

BUT!!!... now.. the chain seems to skip in the back... while on the smalled cog. The cassette doesn't look worn at all.

I realize that its best to change threaded freewheel at the same time as a chain... but this is pretty vintage so.....is that the way i should go?


Yes, you probably should go ahead and get a new freewheel now. They're not very expensive.