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One of my son's friends has turned up with a BMX with a wobbly chainring. The chainring is on a top hat adapter thing that reduces the chainring hole (24mm, I think) to the spindle diameter (19mm, I think), but the adapter is thicker than the chainring, so the chainring wobbles even when the cranks are tight.
I am not wise in the ways of BMX. Can anyone tell how this is supposed to work? Is it the wrong adapter for the chainring? Or should there be another washer to make up the extra width? Or?
It's 100% normal and if you try to fix it you will descend into madness.
How rubbish! Why don't they just make the adapters narrower than the chainring? They'd still do the job of centering it and then it would be clamped properly by the cranks. There's quite a lot of wear on the chainring from the pin on the crank, which I assume is made worse by the looseness.
As a 90's and 2000's BMXer I got sick of pointing out how things should be designed and engineered and just accepted that everything is crap.
Last year I bought my first BMX in 20 years. A brand new complete bike from a shop. It's still crap.
It'll be the wrong size top hat washer, you are correct it could be 19mm, 22mm or maybe 24mm borehole on the chainring with the cranks axle being any one of those 3 sizes.Â
When you say too thick, do you mean the diameter of the top hat washer is too big to fit into the chainring? or the top hat washer when fitted to the chainring sticks out the other side of the chainring bore hole?Â
When you say too thick, do you mean the diameter of the top hat washer is too big to fit into the chainring? or the top hat washer when fitted to the chainring sticks out the other side of the chainring bore hole?
The latter. The diameters seem to be correct, but the chainring is thinner than the narrower bit of the top hat that it sits on, so when you clamp do everything up tight, the chainring can still move from side to side.