help: 'clunk' from rear-end of bike

hotmud · Derestricted Danger Joined: 19 Oct 2011 Karma :

Hi

I have a 2010 Honda CBF125 and after riding it the first few minutes each time there is a single audible 'clunk' from the rear right side of the bike. It only happens once in the first 5 mins or so of riding usually after going over a small bump in the road and never occurs again until the next day's ride. First time it happened I thought it sounded like something from the road hit the exhaust, but obviously it wasn't that.

I had dropped the bike once when I first rode it. Parked on a hill, I stupidly lost balance taking it off its stand and the bike fell away from me towards the pavement. Luckily the only damage was to the right bar-end and a tiny mark to the exhaust.

I've checked the various bolts and nothing seems damaged or loose apart from the bolt that secures the exhaust to the rear footrest bracket. I tightened it but the clunk returned on the second ride after. I also thought it could have been the rear foot peg dropping but it remained up on the last ride.

I'm worried if it might be something that could be dangerous if I don't figure it out.

Any ideas? Could it be from the bracket as the exhaust heats up and expands/settles? Anything else I could have damaged despite not being visible?

thanks and sorry for the long post.

(TL:DR 'clunk' from rear exhaust side of bike after dropping it on that side. Happens once only at start of a ride.)

jimbothe · World Chat Champion Joined: 29 Sep 2006 Karma :

Does that model have the centre and side stand? Is it possible to take a picture of the side of the bike?

I'm wondering if the centre stand spring has been weakened. Bit hard to work out a clunk without hearing it.
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Rogerborg · nimbA Joined: 26 Oct 2010 Karma :

Sight and sound unseen, I'd check is that the drum is secured properly.

I don't know the details of how the CBF's drum is secured, but there should an arm coming off it that bolts on to the swing arm to stop it rotating. If that's loose, then the clunk may be the drum rotating slightly.

Check the bolt again, and see if you can rotate the drum at all by hand, or press the rear brake and watch it (the drum) for any movement.
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hotmud · Derestricted Danger Joined: 19 Oct 2011 Karma :

yep it has a centre stand, and there is a bar attached to the drum. Can't take a pic of mine right now but a highres of the model is here:

https://www.honda-geneve.com/catalog/2010/CBF125/MCB122009SBAm.jpg

Thanks for the tips gives me something to check for tomorrow.

neil. · World Chat Champion Joined: 24 Feb 2008 Karma :

It's likely to be the exhaust contracting/expanding as it heats up, in my case either when I've just started riding or when it's on the drive and the engine is warming up. Mine has done it since day one (brand new bike). It's more of a loud metallic 'click' than a clunk isn't it?

hotmud · Derestricted Danger Joined: 19 Oct 2011 Karma :

I still haven't had a chance to get back on the bike but it's not a thin click or 'pling' like you get when metal expands, it's more of a clonk (better word than clunk actually). It's hollow, like something hits the underside of the exhaust.

jimbothe · World Chat Champion Joined: 29 Sep 2006 Karma :

hotmud · Derestricted Danger Joined: 19 Oct 2011 Karma :

To clarify, this occurs after flipping up the stand and riding for a short while (maybe 2-5 mins), but usually after going over a slight bump in the road IIRC. So perhaps the stand hasn't completely flipped up all the way, is that what a weak spring would do?

(I've just been to the garage to check on the other things - drum is solid, no other loose fasteners I can see).

Next time I ride I will examine the centre stand closely.