Front Freewheel hub on a Trials Bike

[dubhghall]

My son has an Onza trials bike with a front free wheel hub - single speed.

Rotating the cranks leads to the chain going really tight at one point, the freewheel hub squeeks and then as you rotate a bit more all is well again until the same spot on the rotation.
It would look as if something is funny with the freewheel hub - bent perhaps??

Any ideas please?

 

[GilesM]

Sounds like the chainring is worn, they don't wear evenly due to the different amounts of force that is put through the pedals depending on the position of the cranks, example more force when the cranks are at quarter to three, than at six o'clock, this will result is the chain tight spots that you are seeing.

 

[fossyant]

Look for a bent bb axle or a bent hub axle and or bent chain rings - highly likely on a trials bike.

 

[dubhghall]

Many thanks Chaps, will have a look at both. Bit annoying as he has only had it a month! But hardly been off the thing.

 

[GilesM]

If the bike is only a month old, then I think he's bent something, unlikely the chain ring would be worn that much after a month, however if it's a second hand bike that he's only had a month, then it might be worn bits.

IHTH

 

[MartinC]

It sounds like the chainring isn't centered properly. It's rare that the chainring and BB will be totally concentric 'cos of tolerances in manufacture and in the chainring bolt clearances. This will create tight spots in the drive train. You can sometimes improve this by improving the centering of the chainring. AASHTA http://sheldonbrown.com/fixedb.html - look at chain tension

 

[dubhghall]

It sounds like the chainring isn't centered properly. It's rare that the chainring and BB will be totally concentric 'cos of tolerances in manufacture and in the chainring bolt clearances. This will create tight spots in the drive train. You can sometimes improve this by improving the centering of the chainring. AASHTA http://sheldonbrown.com/fixedb.html - look at chain tension

Excellent, many thanks ! Next problem will be trying to get at the bolts when the chain ring is only 18t! I think I will take the crank off first and have a good look, but this is probably the answer - as I can't really see him bending the crank spindle.