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‘Clonk’ noise when setting off

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Paul2129
Renault 5 Driver



Joined: 21 Jul 2013
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PostPosted: 21:57 - 17 Jan 2018    Post subject: ‘Clonk’ noise when setting off Reply with quote

I just wonder if you guys can help me with a little mechanical advice. I have a 3 year old NC750X with 18,000 miles on it. It seems to have developed a weird single ‘clonk’ noise when I set off, or go a few mph and set off again, ie rolling up to a roundabout, then setting off. It’s felt through the left foot peg which makes me wonder if it’s the chain / sprocket. The chain has a scotoiler, has rarely required adjustment, and I was under the impression was still serviceable.
If there’s no problem with wheel bearings, no play in the swinging arm, no unusual play in rear shock...... does that just mean it must be chain/sprockets having a grumble ?

Any advice or pointers would be great

Many Thanks

Paul
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Howling Terror
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PostPosted: 22:08 - 17 Jan 2018    Post subject: Reply with quote

Hi,

could be as simple as worn cush drives rubbers.
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Itchy
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PostPosted: 22:09 - 17 Jan 2018    Post subject: Reply with quote

I think it might be the cush drive rubbers. Perhaps they've perished or worn away or fallen apart.

Years and years ago my tyre man forgot to put them back in and it it clonked each time I moved off . I didn't get far though.

If you think it's the chain just lift the back wheel off the ground (hammer under swing arm works) and spin the rear wheel. Look for tight spots on the chain and wobble on the sprockets front and back perhaps chain is loose and you're getting whip?

If it's not this then things only get more expensive and complex.
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Paul2129
Renault 5 Driver



Joined: 21 Jul 2013
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PostPosted: 07:01 - 18 Jan 2018    Post subject: Reply with quote

It needs a rear tyre, and also a service, so I guess it’s a good time to look into the issue. I’ll let you know if anything is found Smile
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Rogerborg
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Joined: 26 Oct 2010
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PostPosted: 09:25 - 18 Jan 2018    Post subject: Reply with quote

Gearbox in neutral, grab the rear sprocket and try and rotate it forwards and backwards. If there's significant free play (without the rear wheel moving), it's the cush drive rubbers.

I didn't even have to get out of my armchair.
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Pjay
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PostPosted: 09:45 - 18 Jan 2018    Post subject: Reply with quote

Usual suspects are the Cush rubber and a worn front sprocket.
Both simple home fixes, get ya hands greasy and check them out. Should be able to get it all looked over and back together within the hour.
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Paul2129
Renault 5 Driver



Joined: 21 Jul 2013
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PostPosted: 09:49 - 18 Jan 2018    Post subject: Reply with quote

Thanks for the help, I’ll let you know what I find !
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MCN
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Joined: 22 Jul 2015
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PostPosted: 13:52 - 18 Jan 2018    Post subject: Reply with quote

Paul2129 wrote:
Thanks for the help, I’ll let you know what I find !


Maybe best to let Bodyform have a quick look at it for you.

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pompousporcup...
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PostPosted: 15:26 - 18 Jan 2018    Post subject: Reply with quote

Out of interest, do cush drive rubbers wear/break down that quickly on such a bike? All my bikes have no had issues with cush rubbers, have all been 20+ years old and have had 30k+ put on them each year..
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Howling Terror
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PostPosted: 15:52 - 18 Jan 2018    Post subject: Reply with quote

My 250 had less than 20k on it and the cush rubbers were worn...then again it was a thumper (single) and an old one at that.

[rummages through service pdfs]

For my current bikes it doesn't give an interval when to change the cush rubbers, just check for excessive play and replace if necessary.
I changed the cush rubbers on the 944 twin at 35k.
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barrkel
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PostPosted: 14:27 - 19 Jan 2018    Post subject: Reply with quote

pompousporcupine wrote:
Out of interest, do cush drive rubbers wear/break down that quickly on such a bike? All my bikes have no had issues with cush rubbers, have all been 20+ years old and have had 30k+ put on them each year..

Cush drive rubbers were worn on my Brutale when I got it, with lash that went away after replacement; 2012 model with 7.5k miles, bought mid 2017. On 12.5k miles now and still good.

Thankfully it uses the wedge-type rubbers rather than the rubber-covered spacer version used on other MV and Ducati models. Difference between 20 quid and 120 quid.

Wouldn't be surprised if they wear out on a bike that isn't used and parked with them under pressure (e.g. in gear with chain under tension). A bike that likes to accelerate hard probably suffers too.
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