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How does working the nuts on the swing-arms actually cause the chain to be tightened or loosened?

I know chain adjustment has to do with the rear axle. So how do these chain adjuster nuts affect the rear axle?

Is there a diagrammatic representation to show the relationship between the chain and the chain adjustment nuts?

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  • You awarded the answer already? There's nothing in this answer about alignment and ensuring the front and rear wheel are aligned.
    – DucatiKiller
    Commented Feb 24, 2016 at 17:15
  • True. Sorry about that mate.
    – Iceman
    Commented Feb 24, 2016 at 18:44

2 Answers 2

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Adjusting the nuts on the swing arms simply changes the position of the rear sprocket, moving it closer or further away from the drive sprocket, and/or changing the alignment of the wheel.

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The diagram above doesn't show it, but the position of the rear sprocket (along with the whole back wheel assembly) is not fixed, but actually can move along the swing arm(s). This picture should show it more clearly:

enter image description here

When you push the rear sprocket further away, you increase the distance between the sprockets and consequently reduce the chain slack, making it tighter.

On dual swingarm motorcycles, to help with keeping the back wheel aligned, you will see some equidistant notches put in the area your are adjusting. You must adjust on both sides the same distance to keep your wheel aligned. Or if it's not aligned, to start with, then your can use this mechanism to align it.

Don't forget to check your manual for the amount of slack you need to have (the chain doesn't need to be too loose or too tight). Check for wear of the chain and rear sprocket. And clean and lubricate your chain.

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  • Thanks! Another thing, what causes the rear sprocket to move towards drive sprocket? And when there is a load on the motorcycle, the slack reduces right? It means that the rear sprocket is pushed away, causing the cut in slack, if I'm not wrong. So this should result in decrease of slack right, causing the chain to tighten up? So, over time, the chain should become more tighter, if I'm correct?
    – Iceman
    Commented Feb 24, 2016 at 9:36
  • To add to the above question, what is the difference between nuts numbered 1 and 2 in the picture posted?
    – Iceman
    Commented Feb 24, 2016 at 9:48
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    There's nothing in this answer about alignment and ensuring the front and rear wheel are aligned. This is a part of the relationship and extremely dangerous if not done properly.
    – DucatiKiller
    Commented Feb 24, 2016 at 17:16
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    If done incorrectly you get this condition. mechanics.stackexchange.com/questions/26400/…
    – DucatiKiller
    Commented Feb 24, 2016 at 17:18
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    @Iceman The chain always stretches over time it will never tighten, though it may get tight spots. The swing arm pivot point is not concentric with the drive sprocket so the distance between the sprockets varies through the suspension travel so yes the chain tightens and looses with suspension travel, but only momentarily. That's why you leave a little slack when adjusting.
    – Mysterfxit
    Commented Feb 25, 2016 at 16:27
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Slack in chain isn't caused by the rear wheel/sprocket moving closer to the front sprocket. The chain stretches over time during normal use.

To adjust the chain tension you loosen the axle nut and turn the adjuster bolt to allow the rear wheel to move further away from the front sprocket.

I'm not sure about the bike pictured, but on my (old) bike there's another adjustment bolt on the other side of the wheel. You need to adjust them both equally to make sure the rear wheel is tracking the same as the front.

The difference between nut #1 and #2 is that #1 is what holds the bolt in position and #2 keeps #1 from vibrating loose. Two nuts tightened together on a thread are locked in place.

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  • On any bike with a dual sided swingarm and chain final drive, there are adjusters on both sides. Both must be adjusted to ensure the wheel and chain are aligned properly. There's no practical way to avoid the dual adjusters apart from a single sided swingarm design, or shaft final drive.
    – Leliel
    Commented Feb 25, 2016 at 3:19
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    It should be mentioned that once nut 3 is tightened there is no real tension left on 1 or 2. Leaving nut 3 improperly fastened can result in the chain tensioner failing catastrophically (as has happened on my bike)
    – Mauro
    Commented Feb 25, 2016 at 8:48

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