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Cheap BB. Cheap 30t alu chainring.
Cranks came loose, tightened them up at a workshop halfway home but they were knocking like I had a spacer between the BB and frame missing.
Got home and found the BB bearings were shot as I stuck my finger it and spun.
Shoved a new BB in (cheap and nasty, like the first one) and the crankset was binding when spinning it. I figured out it wasn't the BB or cranks, but the chainring. It was bent, and catching on the BB on the way around.
Can I straighten the chainring? Made of alu would it weaken and break in future? How could I do it? Adjustable wrench like using a disc rotor straightening tool?
Anyhow. Forgot to mention how I did it. I was at a tourist location and they were overhauling it, so I was riding around dodging workmen, overgrown bushes, and riding all the stair runs that were empty of tourists. I may have lost control on one big one, hanging off the back cackling in fear, and heard banging on the way down like someone taking a hammer to my hub.
Did the BB bearings blow, making the axle wobble, sending the chainring into the BB to get bent? Or did the chainring bend, crushing the BB bearings?
Recommend brands of GXP 30t 3mm offset chainring that won't bend so easily as a Deckas one? Maybe i'll find one here in China. Or just cheap tat.
My guess is that you bent the chainring by hitting a step, and the BB was shot already. A BB can get quite bad and not be that noticeable when it has a chain on it, you only realise it's shot if you take the chain off and spin it.
https://www.tredz.co.uk/.SRAM-X-Sync-2-Steel-Direct-Mount-Chain-Ring_201228.htm
Probably no stiffer than an aluminium offering but cheap and easy to bend back if needed.
I guess I hadn't assumed I could hit the steps with a 30t chainring being so small. 38t, maybe!
But then, that hammering, metallic noise, repeatedly sounding on the way down...... Guess that actually was the chainring?
I'm safe to just get another cheap chainring then. I was testing out some 165mm crank arms for the fun of it. The arms are cheap (£27.25 for cranks, BB + chainring) and dangerous looking with high cutouts, but they survived a fair bit of hammering. I'm sure someone raised these before:
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@bigginge, if I told you 7050-T6 chainrings where I am cost £6 and upwards, would that shock you? And this issue wasn't caused because of cheap tat, but a violent interlude with a fair number concrete steps.
Bending steel back could work, but If it trashed the BB like happened today, then the crank arm would just come loose again and the bike would struggle to limp home again. Might as well cadge a lift, and pay £6 for another chainring, haha.
I doubt the impact hurt the BB significantly unless it was already trashed.
When the chainring hits the ground the force is traveling from the ground through the chainring, crank, pedals to you (the center of mass of the whole bike/rider). It's not going via the BB.
You could fit a bashring/guard if it's a regular issue?