Rear sprocket nut clearance

Squeaky back brake? Hard to control at 30mph/40kph?
GhostMile
125cc
125cc
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Year: 2011
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Model: SMT

Re: Rear sprocket nut clearance

Post by GhostMile » Tue Apr 19, 2016 7:53 pm

Magic Wand wrote:Weird problem, man...

Did you change the ball bearings in sprocket holder and got wrong ones (to thin)? Naeh... that woun´t make a difference, because the 2 spacer bushings in the sprocket holder are the same.
From your pictures of the new sprocket mounted on the hub, it looks like the nuts are not enough tightened or the new sprocket is about 0,5 mm thicker than original. That would maybe explain the problem.
I have mounted a 38 t sprocket some weeks ago (from Sunsstar) and that works great.

/M
Thanks for the insight. :)

Well, new sprocket is not 0,5 but the whole mm thicker, as stated in the beginning, but that is the case on many other smts, with no issues.
Good point about the thinner bearings, but I think I checked that too (numbers on it).

I will post eventually what it was... That is if I ever find out. :)

Magic Wand
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Re: Rear sprocket nut clearance

Post by Magic Wand » Tue Apr 19, 2016 8:36 pm

GhostMile

Maybe you got the wrong rear sprocket?! It could fit to another model year, but not to your bike?

Could you measure the distance between the left and right swing arms, at the point where the spacer bushings are located (when wheel in place)?
I will measure at my bike, maybe tomorrow if I find time.

How close does the sprocket support/holder get to the wheel (where the damping rubbers are seated?) It should be no distance at all, or very very little.

Are the spacer bushings in the sprocket support/holder all the way in, into the ball bearings? I don´t remember, but do the both spacers have the same measures? Or could it be that you mixed them up and mounted on wrong side?

/M

Magic Wand
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Re: Rear sprocket nut clearance

Post by Magic Wand » Thu Apr 21, 2016 3:19 pm

I have made some measurements:
IMG_1824.jpg
At this first image you can see that clearance between sprocket nut and inside of swing arm is narrow. (Imagine how close it will be when mounting 41 t sprocket... (the chain have to be adjusted and sprocket nuts will get more in front ("closer" to the swing arm)). I bet there is not more than 0,5 mm clearance in such scenario...)
IMG_1825.jpg
Second image shows that the sprocket support/holder unit is close to the wheel/rim. It also shows the spacer is about 2 mm out from sprocket.
IMG_1826.jpg
Third image shows the spacer on right side (brake disc side).
IMG_1827.jpg
The width/space between the left and right (in)side of the swing arm: 22,5 cm.
IMG_1828.jpg
IMG_1829.jpg
IMG_1830.jpg
IMG_1831.jpg
IMG_1832.jpg
Thickness of the 38 t (Sunsstar) sprocket: 3,5 mm.

/M

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