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Discussion Starter · #1 ·
Hi There, My son owns a cbr300r which we recently purchased. The chain tension is being weird. I checked and re-tensioned the chain, but on a rotation of the wheel found that the tension went from just right to extremely overtight and difficult to turn. It seemed to be in one particular place in the chain but on inspection, the chain looks OK. I read that it could be irregular wear on the sprockets but the tightness only seems to occur on a full rotation of the wheel. There doesn't seem to be any noticeable movement in the swing arm bearing or wheel bearing.
So is there anything else that could cause this? or should I just get a new chain or the whole chain and sprocket kit?
 

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You didn't say how many Miles/Kilos on the bike. So, I'm speaking in general here. Most mfg's suggest somewhere in the range of 20mm-30mm slack, which may seem loose, but isn't. Having said that, if the chain has a link that's binding and not floating freely, you can't 'fix it', you'll just need to replace the chain. It's better to replace chain and sprockets together, but If you have low mileage and the sprockets show no wear.. IMO, it's a judgement call. The costs of new OEM sprockets are reasonable. (Less than $50 US for both), and replacement of both sprockets and a chain, would require a thorough looky-loo of the whole drive system during installation, which would give peace of mind... and let you know exactly where you stand when completed. Good Luck.
 

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@airhead83 has covered this nicely but a wild card possibility I'll throw out there is that your rear sprocket has been poorly machined and the outside diameter (the teeth) is not concentric to the inner pitch circle diameter that the sprocket bolt holes are drilled on. I know this scenario as I make up my own aluminum sprockets for my bikes from blanks and if I dont get this part of the operation bang on it creates the exact scenario you describe. More likely though it is a stiff/binding link.
 

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I had a stiff link on my 2016 CBR at 10K miles. Couldn't move it even with molegrips. Replaced chain with a new DID VX. The chains fitted OEM are the cheap ones.
 

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Discussion Starter · #5 ·
I went ahead and ordered a (standard) chain and sprocket replacement kit which I now have, but I am wondering if anyone here has the recommended torque settings for the rear sprocket bolts and the axle, please?
 

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Rear axle: 88 N·m , 9.0 kgf·m, 65 lbf·ft
Rear sprocket nuts 74 N-m , 55 lbf -ft

Personally I dont use torque wrenches and I'd be wary of that rear sprocket nut setting as it sounds like a lot for a 10mm thread. I found it on the CBR250R forum.
 

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Non concentric sprockets are not unknown. The OEM rear on my CBR was not circular so I replaced it.
 
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