YBR125 strange chain tension/noise advice

ruprechtmonke... · L Plate Warrior Joined: 15 Sep 2019 Karma :

Hi all, got a strange issue with my bike. I bought it a couple of months ago to practice on due to my test being delayed because of the lockdown. It's had a new chain and sprocket set but I noticed when checking that the chain had too much slack. I've adjusted it to about 25mm (manual states 20mm - 30mm). However in doing this it developed a noise when riding which I can best describe as an almost rubbing/whirring that comes and goes every few revolutions of the rear wheel and increases/decreases with speed. Seems to happen more when the throttle is applied. I thought it may have always done this and I hadn't noticed so to test this theory I loosened off the chain a bit and took it for a ride. The noise went. I've checked both the front sprocket and wheel alignment, etc and all looks good (I've also changed the oil on the bike). The back wheel spins freely when on the centre stand. Now obviously I don't want to ride about with a loose chain so does anyone have any ideas what may be causing this? Thanks

Riejufixing · World Chat Champion Joined: 24 Jun 2018 Karma :

Check the tension at various points. So, rotate the back wheel nearly half a turn, check. Do it again, check. And again, until you have checked a few points. Is it tight anywhere? Perhaps it is. You will have to say!

jaffa90 · World Chat Champion Joined: 06 Apr 2016 Karma :

https://www.bikechatforums.com/viewtopic.php?t=330781

steve the grease · Crazy Courier Joined: 26 Jan 2018 Karma :

I think the 20-30 mm is when you are sat on the bike. It's probably miles too tight if you adjusted it on the stand. As you apply weight ( like sit on the bike) the chain gets loads tighter , loosen it off and see if it improves.
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Nobby the Bastard · Harley Gaydar Joined: 16 Aug 2013 Karma :

Most manuals state tension should be checked unloaded and on the side stand.

Is the alignment t of the back wheel been checked?
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ruprechtmonke... · L Plate Warrior Joined: 15 Sep 2019 Karma :

Riejufixing · World Chat Champion Joined: 24 Jun 2018 Karma :

ThatDippyTwat · World Chat Champion Joined: 07 Aug 2016 Karma :

ruprechtmonke... · L Plate Warrior Joined: 15 Sep 2019 Karma :

Thanks for the tips. So I've measured from a fixed point and the wheel is aligned, took the chain guard off and noticed the part nearest the front sprocket was slightly bent and had a 'clean' bit inside possibly where the chain was rubbing? I bent this back and cleaned/lubed the chain for the first time since getting the bike. Result is the noise has gone away so one or both of these things sorted it. Cheers