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Bent chainring or bent spindle?

PB Forum :: Dirt Jumping & Street
Bent chainring or bent spindle?
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flag cmc4130
Posted: Oct 24, 2014 at 10:00 Quote
THATdjGuy wrote:
.... but i have alot of assignments to do this weekend so i might not get around to it that quickly
thanks

hey, we don't want to hear your excuses. get on this. it shoulda been fixed YESTERDAY! hah hah!
flag THATdjGuy
Posted: Oct 24, 2014 at 17:45 Quote
cmc4130 wrote:
THATdjGuy wrote:
.... but i have alot of assignments to do this weekend so i might not get around to it that quickly
thanks

hey, we don't want to hear your excuses. get on this. it shoulda been fixed YESTERDAY! hah hah!

i tried pushing them together and the sproket still moves and the top hat isnt bent so im thinking it is the spindle or bb. at its closest point the sprocket is like 1mm from the frame and at the furthest it is about 4-5mm so there is quite alot of movement
flag THATdjGuy
Posted: Oct 25, 2014 at 2:43 Quote
THATdjGuy wrote:
cmc4130 wrote:
THATdjGuy wrote:
.... but i have alot of assignments to do this weekend so i might not get around to it that quickly
thanks

hey, we don't want to hear your excuses. get on this. it shoulda been fixed YESTERDAY! hah hah!

i tried pushing them together and the sproket still moves and the top hat isnt bent so im thinking it is the spindle or bb. at its closest point the sprocket is like 1mm from the frame and at the furthest it is about 4-5mm so there is quite alot of movement

i was dumb enought to only look at one side so ill put another top hat in tomorow and see it it makes a difference.
flag ricar
Posted: Oct 25, 2014 at 4:27 Quote
That's not a lot of movement. If it's only 3-4mm or so I wouldn't worry about it unless it's causing problems, but that shouldn't be an issue. Most often you'll find the wobble is in line with the chain ring bolt on the crank arm, nothing is ever perfect.
flag THATdjGuy
Posted: Oct 25, 2014 at 14:27 Quote
I think it is the movement that is causing the chain to go tight and loose like cmc said on the first page.
flag THATdjGuy
Posted: Oct 26, 2014 at 1:17 Quote
I've put in a new top hat and it has made the wobble smaller but there is still some but i'm guessing it is just normal. the chain still has a little bit of a tight and loose spot but as you said that would be normal.

Also any ideas why my left crank is coming loose?
flag CptKlink
Posted: Oct 26, 2014 at 1:38 Quote
I do know that a little wobble from side to side is normal. And the chain going from tight to a little lose to tight again only a little bit is actually unavoidable because NO sproket/chainring is perfectly round no matter the brand, model or material there all slightly oval in shape not much at all but enough to notice the chain going from light to loose. Now keep in mind the lesser quality sprokets/chainrings are even more oval shape so makes the chain problem even greater.
flag THATdjGuy
Posted: Oct 26, 2014 at 2:24 Quote
thanks. on chain reaction it said the sprocket i brouhgt was down from 110 AUD so it seems like a pretty good sproket. its an amimal Spockey baloba
flag ricar
Posted: Oct 26, 2014 at 6:04 Quote
You could make a perfect sprocket and match it to a perfect crank but you will NEVER get a chain to stretch evenly. That is the biggest issue with the tight and loose spot. You will never measure it because each link will stretch differently but it's usually extremely minimal, but different spots will stretch differently.

If that's what you are trying to fix, good luck.
flag CptKlink
Posted: Oct 26, 2014 at 10:28 Quote
Well Animal makes quality products so I would consider that a higher quality sproket. There's actually a little LBS in a small town next to me his speciality it might sound weird but he sync's the Front and rear Sprocket's be it chainring or direct mount sproket or freewheel or cassette. So when he does it right when the Front drive goes through its tight spot and starts to go loose he will then make the rear drive start to go in to its tight spot so it will alternate from front to tight to back to loose and vice versa if that makes any sence. He says this works best for singlespeed bikes but can work for multispeed bikes if your drivetrain and deraillers and shifters are all perfectly meshed which he does a very good job at as well.
flag ricar
Posted: Oct 26, 2014 at 19:41 Quote
Except the front and rear sprockets rotate at different RPMs. How can you synch them if they don't end up in the same place every rotation?

EDIT: Not only that, the chain will have spots that stretch more than others, how could he account for this? Not saying he does not have some process, not saying it is BS, just trying to figure out how that could be done.

Also you mention gears and that throws another wrench into the "rotational alignment" if you will, between front and rear gears..... I can't figure that one.
flag THATdjGuy
Posted: Oct 26, 2014 at 23:09 Quote
So any ideas why my left crank keeps coming loose?
flag CptKlink
Posted: Oct 27, 2014 at 10:35 Quote
ricar wrote:
Except the front and rear sprockets rotate at different RPMs. How can you synch them if they don't end up in the same place every rotation?

EDIT: Not only that, the chain will have spots that stretch more than others, how could he account for this? Not saying he does not have some process, not saying it is BS, just trying to figure out how that could be done.

Also you mention gears and that throws another wrench into the "rotational alignment" if you will, between front and rear gears..... I can't figure that one.

Ya he does say thats its not in sync every rotation and its not perfect but he says that after I think it was 15 to 20 full rotations accounting for different gear ratios (speaking singlespeed only) Its back to where it started in sync again so in a sense will create a more uniform chain stretch not perfect but still better then just slapping the chain and sprockets in any location. Like he says it isen't perfect and it will always go out of sunc and back in but its the best that can be done unless you find a way to make a perfectly round sprocket and freesheel/cassette and also what throws off the chain stuff is the direct mount sprockets like to see mostly on BMX's the center hole for the crank spindle is usually never exactly in the center of the sprocket.
flag ricar
Posted: Oct 27, 2014 at 18:53 Quote
THATdjGuy wrote:
So any ideas why my left crank keeps coming loose?

Arm or pedal? Or both?
flag THATdjGuy
Posted: Oct 27, 2014 at 23:16 Quote
ricar wrote:
THATdjGuy wrote:
So any ideas why my left crank keeps coming loose?

Arm or pedal? Or both?

Its the crank arm that comes loose. Specifically the bolt on the side of the crank that comes loose not the pinch bolt and also the bolt on the right crank that holds the sprocket comes loose a little bit. Also my current bb bearings are rattling but i have new ones on the way. I think it it the vibration is the bb that are causing them to come loose but i'm not really that sure.

 


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