Rear chain large difference between tight and loose spot

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packrat48
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Rear chain large difference between tight and loose spot

#1

Post by packrat48 » Sun Apr 14, 2019 1:33 am

One and a half inch difference between loosest and tightest spot.

Ridged frame, mechanical brake. Unknown chain age. New front sprocket on new reproduction panhead transmission. Older rear drum/sprocket-visually sound.

On most of the bikes I have and have had there is a tight spot on the rear chain, however this bike upon reassembly has a one and a half inch difference. Never having had that much I think I must be missing something here. I have seen worn or warped sprockets and sloppy chains, misalignment cause this, but never that much difference..

In your experiences what would likely causes of that be, what to check first and/or replace?

Appreciate your experiences, assistance, ideas.

Thanks!



Robbo
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Re: Rear chain large difference between tight and loose spot

#2

Post by Robbo » Sun Apr 14, 2019 2:03 am

Stretched chain, get a new one and you should be good to go.
I haven't seen anything quite that bad but my shovel was making weird noises like knocking. Turn out it was the bike picking up the chain stretch each rotation.
To rule out any issues with the sprockets, mark the middle of the loose section and install the chain half a rotation different. Check the tension again to see if the loose bit is in the same spot.

1950Panhead
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Re: Rear chain large difference between tight and loose spot

#3

Post by 1950Panhead » Sun Apr 14, 2019 2:04 am

In your experiences what would likely causes of that be, what to check first and/or replace?
My guess would be the chain.
You can check the sprockets by clamping vise grips near sprocket edge then spin read wheel, turn engine sprocket with socket giving rough estimate of being concentric.

packrat48
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Re: Rear chain large difference between tight and loose spot

#4

Post by packrat48 » Sun Apr 14, 2019 3:46 am

Thank you! Seems like a new chain and recheck...

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Re: Rear chain large difference between tight and loose spot

#5

Post by Panacea » Sun Apr 14, 2019 5:37 am

Grab the chain at the rear of the sprocket and see how much you can pull it off of the teeth, if you can see thru the teeth under the chain, it's shot. 3/4" difference between the tightest spot and loosest spot would be normal from my experience, It would be a good idea to check the sprocket when you rotate the wheel to see how concentric it is. also the condition of the teeth, are they sharp and pointy?

packrat48
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Re: Rear chain large difference between tight and loose spot

#6

Post by packrat48 » Sun Apr 14, 2019 6:01 am

Fairly pointy, yes. Grabbed the chain and can not see thru the teeth at all.

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Re: Rear chain large difference between tight and loose spot

#7

Post by nan00k » Sun Apr 14, 2019 8:18 am

out of interest what is the play/condition like on the primary chain?

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