BMX - 3 piece cranks

i put them on and have a hi/lo spot on my chain
any remedies for this?
will chain tensioners work?

Nope, it means your sprocket is not aligned on the spindle. If it wasn't out of round before you installed the cranks it could mean a couple things. First, visually check to see if your sprocket wobbles side to side or up and down when you turn the cranks.

Side to side wobble means there is either a spacer or a space of some kind between the sprocket and crank arm. If this isn't the case it means either your sprocket is bent or your crank arm needs to be properly faced with expensive tools.

Up and down wobble either means the sprocket is not centered on the spindle or the sprocket itself is out of round. Did you ensure good sprocket fit on the spindle? If your cranks use a 19mm spindle (Profile standard), you'll probably need a little spacer that pops into the spindle hole on your sprocket. Did you use that or put the sprocket on loose? Is the spacer thicker than your sprocket, resulting in a space between the sprocket and crank arm (see above)? If that checks out and the sprocket fits cleanly on the spindle you've probably just got a cheap sprocket that's not perfectly round.

cranks faced w/ expensive machinery ??? what like a bench grinder...
we're talking BMX here, not F1 racing!

if you used your existing chainring, did you get a space for the hole that fits on the spindle. The ones sized for 1 pc cranks are larger i think. if there is no spacer, it has probly shifted to give you what appears to be an off-round sprocket....

cranks faced w/ expensive machinery ??? what like a bench grinder...
we're talking BMX here, not F1 racing!

It depends on your tolerance for dropping chains, bending sprockets and smashing cassette bearings. Mine's pretty low.

As a mechanic I get to see all sorts of janky backyard solutions people come up with to avoid paying a bike shop 10 bucks, and it's pretty ridiculous. BMXers are so notorious for this, a shop I worked for had 'BMX TOOL' written on the biggest hammer and crescent wrench in the shop. Most BMX bikes ride like crap and most BMXers think that's all right, long as their parts are stamped with the most popular logo.

Mmmm, shop tools.

Anyway, he's put the sprocket on with the spacer all jacked up. I did that the first time I worked on a BMX with a Euro BB. It slipped while I was racing, and I count myself lucky that I only broke the chain on one side plate.

Well, a facing tool is definitely expensive, but many shops have facing tools in house and may be able to do something. I wouldn't expect this to be the case as decent cranks should come properly faced.

Most often the sprocket is slightly out of round, or it is off angle slightly.

Sheldon Brown has some info on his site about realigning a bent chainring. I saw it about a month ago. I'm too lazy to search for it again.

Well, a facing tool is definitely expensive, but many shops have facing tools in house and may be able to do something. I wouldn't expect this to be the case as decent cranks should come properly faced.

Most often the sprocket is slightly out of round, or it is off angle slightly.

Right, thank you. I don't think I was clear enough on order of likelihood...a sprocket out of round is the #1 culprit for a thing like this, most of the others are pretty remote (but not unheard of).

part of the fun of bmx is inventing ways to hood-rig your bike.

It's just installed incorrectly. That's my bet.

Nope, it means your sprocket is not aligned on the spindle. If it wasn't out of round before you installed the cranks it could mean a couple things. First, visually check to see if your sprocket wobbles side to side or up and down when you turn the cranks.

Side to side wobble means there is either a spacer or a space of some kind between the sprocket and crank arm. If this isn't the case it means either your sprocket is bent or your crank arm needs to be properly faced with expensive tools.

Up and down wobble either means the sprocket is not centered on the spindle or the sprocket itself is out of round. Did you ensure good sprocket fit on the spindle? If your cranks use a 19mm spindle (Profile standard), you'll probably need a little spacer that pops into the spindle hole on your sprocket. Did you use that or put the sprocket on loose? Is the spacer thicker than your sprocket, resulting in a space between the sprocket and crank arm (see above)? If that checks out and the sprocket fits cleanly on the spindle you've probably just got a cheap sprocket that's not perfectly round.
listen to this guy! listen to this guy!


couldnt have said it better myself..:)!

yea what he said.

yea what he said.
yeah, what i said, he said....