significantly uneven tension on new chain & sprox

[trevor saxe-coburg-gotha]

Last month I replaced chain and sprockets - chain was a genuine DID x-ring.

What I noticed quite quickly was that the chain was as uneven in tension as an old, quite worn one. I was really pissed off because it wasn't cheap - and was a reputable, renowned brand.

My mate had encountered something similar - but fortunately for me, has a been riding ten times as long as me, and spent his life fettling around with bikes. Also, he's analytical and methodical.

He noticed that when he'd marked the slackest point on his new chain, then turned the back wheel a few times, the marked slack point became tight. Wtf.

Clearly, something else was creating slack, leading to uneven tension along the chain's run. Just as it was with mine.

Next culprit in line seemed to be the rear sprocket. And yet a few tests suggested it was true laterally and vertically. Except it wasn't.

In short, what had happened - in both cases (mine and my mate's chains) was that an eccentricity in the rear sprocket was creating uneven chain tension. The sprocket nuts had not been tightened with sufficient care and evenness - i.e. in a star pattern. Once slackened off and re-tightened with a bit more diligence - i.e. first nut, opposite nut and repeat - the chain was evenly tensioned along its run.
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"Life is a sexually transmitted disease and the mortality rate is one hundred percent."

Mobylette Type 50 ---> Raleigh Grifter ---> Neval Minsk 125

[Riejufixing]

I have just this afternoon had a similar issue. The rear wheel hub on a 125 has projecting lugs, machined concentrically with the bearings, which locates the sprocket which slides over them. The sprocket had previously come off, by the look, and worn the lugs, and there was the thickness of a piece of paper between the inside of the sprocket and the lug on one side (6 bolt attachment) with the sprocket pushed "sideways" and off-centre. Repositioning the sprocket fixed the issue. In future I will look at any clearance when refitting, and use a bit of shim all around if need be.

[Pete.]

As above eccentric sprocket mount or ruined sprocket carrier bearing. Possibly knackered cush drive. The fact that ANY part of a new chain is pulling tight says that you have it adjusted with too little play.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[MCN]

Mark the sprocket and chain where is is tight.
Rotate until it is tight again. If the sprocket is out the tight bit will align at the same position on another bit of chain. (until it's been around a few times)

Bolts 'should' be 'fitted' bolts with no play in the holes.
If it was slack then the bolts and sprocket can wear.
New bolts and sprocket should resolve problem.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[trevor saxe-coburg-gotha]