Chain tights spots and rear sprocket oscillation.

Taipan

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Something I learnt along time ago is chain tight spots is really a misnomer. When the chain gets tight in its revolution, its mostly because, rusted links not withstanding, the rear sprocket is oscillating. I had this once before where it was enough to cause concern, but its something I've not normally worried about and chain adjustment has been fine when the adjustment allows for it.

On this bike the difference in chain tension when you rotate the wheel is alarming! So I have loosened off the sprocket nuts, turned the wheel until the chain slack is tightest, then tapped the rear sprocket towards the front. I couldn't really see it move, but I know have an even but over slack chain all round!

I expect many of you know about this, but thought i'd mention it in case you didn't. I can't see a make on the sprocket, but will check the s/history to see if its in there and named? I'll adjust it properly now and see how things are in a couple of miles. Any movement and i'll fit a OEM one, but last time I did this, it sorted the problem permanently.

Speaking of adjusting the chain: Like most of us I never know what to ask for on birthdays or at Xmas, but one year my love of gadgets lead me to ask for a tru tension chain monkey. It grips the sprocket and shines a laser dot up the chain line so you can see if things are in line. Anyway, it was unwrapped and then found its way unused to the attic. I just found it up there and thought as I'm doing what I'm doing I'll give that a go. Not that i need it of course, been working on bikes for years and I certainly know how to align a rear wheel ffs! :confused::oops::D



 

showkey

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This topic of tight spot in chain rotation was discussed in depth going back over 8 years.
The theory was the rear hub sprocket mounting area were out of round or slightly elliptical. Or the sprockets were Out of round.
Both theories were found to have no merit when measured with a dial indicator.

There is a small clearance between the hub and sprocket which allows the sprocket to slip on and off the hub. This small clearance is also present on the mounting bolts.
This clearance is very small so movement of the sprocket on the hub is so small there is no significant adjustment to the so called out of round problem.
Remember the sprockets are stamped not machined. They not perfect but the stamping does not need to be perfect.

The chain “tightness” change with wheel rotation is caused by the chain links binding. This has been proven and documented many times.
 

Taipan

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A dial gauge will certainly be more accurate than my neanderthal hammering, so I consider myself corrected. As I almost corrected the tight spot, but certainly improving, I'm wondering if I got lucky by hammering, well tapping, the wood against the chain and sprockets dislodged some rust on a link or two to give me the result I got? Oh well, it's all good as they say...
 
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