BMX - Clarification on crank/chainwheel interface?

i might be using a few incorrect terms here...but you'll know what i am refering to. the small bolt that attaches the chain wheel to the crank arm is what i am wondering about. i haven't dealt with this set-up since probably the 80's...at that time i was too young to have worked on things so basically i never dealt with them. :D

question is this:

1) seems kind of like a delicate design...are there ever problems? does the bolt ever shear off?

2) does backward pedal/crank pressure cause fore and aft movement in the chain wheel slot?? it just doesn't look secure to me...or maybe only secure in the forward direction because the hole looks significantly larger than the bolt.

thanks

1) If you're talking about the sprocket bolt, well, I've never broken one.
2) How would it move? The slot for it is only as wide as the bolt is.

The hole is usually slotted to compensate for slightly different placement of the bolt on the crank arm. And you shouldn't worry yourself too much...it's a beefy steel bolt sunk into a beefy steel crank arm. I've not had problems with the design so far, and solid sprockets are MUCH stronger than spiders/rings.

2) How would it move? The slot for it is only as wide as the bolt is.

okay...like i said i never held these parts in my hand...only MTB stuff. this is new to me. :)

as i was looking at pics, it looked as though the width of the slot was much great than the bolt...that is what made me think about play developing.

...but thanks for clarifying guys!

If you don't run it tight enough play can appear as the threads dig into the sides of the sprocket hole. IMO it's a ****ty way to attach a sprocket and it's a leftover from the days of 1pc cranks. A bullseye style method of attaching them would be much better.

Oh yeah, don't run a spacer between the crank arm and the sprocket at the sprocket bolt or at the axle, not only does it increase the leverage on the bolt but it reduces the amount of working thread by quite a bit.

If you don't run it tight enough play can appear as the threads dig into the sides of the sprocket hole. IMO it's a ****ty way to attach a sprocket and it's a leftover from the days of 1pc cranks. A bullseye style method of attaching them would be much better.

Oh yeah, don't run a spacer between the crank arm and the sprocket at the sprocket bolt or at the axle, not only does it increase the leverage on the bolt but it reduces the amount of working thread by quite a bit.

BMXers don't break sprockets with torque forces, they break sprockets by smashing them on curbs. The single bolt is MUCH stronger under those types of stresses. More bolts = more stress risers.

BMXers don't break sprockets with torque forces, they break sprockets by smashing them on curbs. The single bolt is MUCH stronger under those types of stresses. More bolts = more stress risers.

Curbs? O rly

My reasoning is the more support a sprocket has, the stronger it is. The fact there are more sprocket holes is irrelevant, because only one of them is going to be under real stess from a sprocket trick at any one time. Now bearing in mind that with the current set up the sprocket bolt doesn't do a whole lot to support the sprocket when you're doing a sprocket trick, maybe you'd like to explain to me how it's stronger?

Curbs? O rly

My reasoning is the more support a sprocket has, the stronger it is. The fact there are more sprocket holes is irrelevant, because only one of them is going to be under real stess from a sprocket trick at any one time. Now bearing in mind that with the current set up the sprocket bolt doesn't do a whole lot to support the sprocket when you're doing a sprocket trick, maybe you'd like to explain to me how it's stronger?

Because when you're doing sprocket tricks, the impact is taken by a nice strong spindle, not a weak-ass bolt.

It's not thos sorts of impacts that **** dprockets up, it's lateral ones. Besides, in my theoretical SupaDupa™ cranks there would still be something supporting axle hole, the additional sprocket bolts would be to counteract the lateral forces.
Imagine a cross between this http://www.odysseybmx.com/dailyword/archives/wombolttech.jpg
and this
http://www.bikepro.com/products/cranks/crk_jpg/b_bullseye_cranks.jpg

Crazy, I just got back from riding today early because my sprocket bolt(on my crank arm) was cracked almost all the way off. They're Redline Monster cranks, and I am surprised that they have lasted this long(two years), and at one point they bent so much that I had to heat up one of the arms with a blow torch and bent it back with a sludge hammer. I obvously didn't have enough money to get new cranks at the time. Luckily now my Odyssey 41 thermal cranks are on their way. Lucky meeeeee! : )