Bicycle Mechanics - Chain Trouble

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alan
01-15-02, 04:25 AM
When the left pedal is up and the right pedal is down the chain is really tight but when the left pedal is down the cahin is loose. What's wrong? :o
It is a B.M.X bike.

Campag Fetish Boy
01-15-02, 04:42 AM
The most likely cause is that you have a "not quite round" chainring or freewheel.

See diagram attached On the second drawing I forgot to say that chain tension would be at it's highest in this configuration.
RainmanP
01-15-02, 08:28 AM
Do you by any chance have Shimano Bio Pace chainrings? They are kind of rounded square in shape and there for act like out of round rings, because they are. They would probably have yellow logo on the side saying "Bio Pace".

If your rear wheel is installed out of line this could happen, but you would probably notice.

D*Alex
01-15-02, 03:13 PM
I'll bet your spindle is bent.
alan
01-15-02, 04:41 PM
Do you mean spindle or sprocket?
Dirtgrinder
01-15-02, 04:43 PM
I'm thinking he means the BB spindle.
alan
01-15-02, 08:37 PM
I posted this on another forum and they said it was the sprocket I stuffed up.
pat5319
01-15-02, 10:25 PM
Don't worry about tension difference, it happens on ( almost) ALL one speeds with one piece cranks, be they BMX, Cruisers etc. If I ever run across one with perfect tension during the entire circle I'll be very surprised.

Ride With Serenity
Pat
alan
01-16-02, 01:53 AM
There are 3-peice cranks.
john999
01-16-02, 06:13 AM
If you have the chain adjustment bolts at different lengths it will cause this problem.
alan
01-16-02, 04:23 PM
I think I have got the chain right now. I ended up only tightening one tensioner, but I can hear a creak. I can't tell if it is from the freewheel or sprocket. :(