I picked up some 160mm crank arms for my sons bmx bike (we're new to bmx racing) and I can't figure out how the chain ring detaches from the right crank arm. It looks like it could be a weird kind of nut but it didn't move when I applied light force to un screw it. Any help would be appreciated.
Bike is a gravity superfast and here's some pics.
by Key_Introduction_469
12 Comments
Sorry this pic didn’t post
https://preview.redd.it/0xfz7x24oeof1.jpeg?width=3000&format=pjpg&auto=webp&s=2707835b2d559d0768c9a29eafb97b41c6e897cb
You don’t. Full new crank set time.
I would have initially agreed with the other poster that this is one piece, but then it doesn’t make sense for the chain ring to have the hole for the bolt on a 3 piece crank.
I’d maybe try some *light* percussive persuasion.
The chainring looks like a standard one for a one-piece BMX crank (round hole with a hole aligning with the crank), which are replaceable. This isn’t a one piece crank though, and the lockring that normally holds the chainring on isn’t there. Could be that this isn’t user servicable, but it’s weird that they’d use a standard design chainring in that case. That grooved black ring can’t be unscrewed?
Yeah, that’s not coming off.
Angle grinder, bench grinder, hammer…. they are not meant to come apart.
Looks like you need a crank arm puller tool.[Park Tool](https://youtu.be/uO_GzqqJTXU?si=cxnujBeb6kneaabs)
Thank you, everyone. I realize I can’t use these crank arms and need to buy a full setup. I appreciate the help.
Looks to me like it is pressed on. A machine shop with a hydraulic press may get it off for you, but it would probably be cheaper to buy a new one.
You might try asking in a bmx specific subreddit such as r/bmx or r/oldschoolbmx
Almost looks like a bb cup tool could unthread it. Similar to a disc brake rotor. Hard to tell from the picture
This is a cheap crankset with a non-replaceable ring. You get what you get unless you buy a different crankset.