Chain skipping. Could sprocket be worn before chain?

Letterman

10 mW
Joined
Mar 2, 2020
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22
I've replaced the chain and cassette (8 speed) about 250 or so kilometres ago.

There's no measurable wear on the chain (tried 2 different wear checkers, and measured with a ruler), however the chain has just started skipping on the 13T sprocket under heavy load.

I spend probably 85% of the time in this gear and sprocket, as it is my "cruising gear".

The cassette is a Shimano CS-HG51-8 and supposed to be made from steel, the chain is a KMC X8.

Is it possible that the sprocket is worn enough for the chain to skip, prior to the chain wearing?
I always thought that you should be able to go through 3-4 chain replacement prior to having to replace the cassette or sprockets.

Anything I should check on the derailleur or anywhere else to get rid of the skipping, before I try to replace the cassette again?

Thank you for your help.
 
Is the chain sized correctly for length? If it's too long it's possible it doesn't have proper tension.
 
try adjusting the cable tension 1/2 turn at the adjuster; might be slightly off and only notice under load
 
Without seeing it, it's just a guess, but you may not have enough chain wrap on the small cog. Make sure your derailleur is not stuck in a rearward position or frame mount pivot is not frozen, which will keep the top pulley wheel from a closer- more forward position, thereby grabbing an extra tooth or so and greatly reduce the ability of the chain to lift. Also make sure your not trying to wrap more "teeth" than your derailleurs capacity. Next thing to check is that it is not trying to shift gears. Pulley wheel should visually line up directly with the cog and cable slop minimal when in the smallest cog.
 
speedmd said:
Make sure your derailleur is not stuck in a rearward position or frame mount pivot is not frozen, which will keep the top pulley wheel from a closer- more forward position, thereby grabbing an extra tooth or so and greatly reduce the ability of the chain to lift.

Thank you. The top pulley isn’t as close to the smallest cog as it could be and certainly not touching the largest cog either but the B screw is already all the way out. I read somewhere there should be a 5-6mm gap and it’s definitely more like double that.

Any tips on how to adjust that?
 
nevermind, i may have misread it...did you say its not close enough or two close? either way chain length

Depending on the train and the set up, I have found that certain chains are not long enough to work with full size 26/36/48t cranks. For example, and a lot of hybrids I have to use KMC chains rather than sram as 116 links are required and sram is only 114

If it is too close, shorten it. If it is too far consider a longer chain if you can't make up for it with the b screw
 
Thanks.

I’m using parktool’s chain plus 2 links method to determine the correct length of the chain, which seems to be a common method.
And yes, I have to add links to a standard KMC X8 as it’s not long enough for my 48T/32T combination and my 28” wheels.

Is there a chance that the chain length method I’m using results in too long a chain?

size_014.jpg
 
Is the rear derailleur a long cage or a medium cage (distance between pulley wheels)? The mediums in my experience always run better with a shorter chain. First photo on the park tool page you reference, the old rule was to get the cage no flatter than a 45 degree angle. With a medium cage and set that way, the chain will be sloppy most times when shifting to the small cog.

You may be over the capacity of the rear derailleur. Common when running triple crank with a double rear setup. No issue as long as you don't completely cross chain it.
 
Thanks

I’m running a single 48T chain wheel at the front and an 8 speed 11-32T cassette at the back.

The derailleur is a Shimano Altus, M310 I believe, which should have a total capacity of 43T.
 
Running a single chain ring, just shorten the chain to get more wrap of the small cog. Make sure your adjusting the b screw to move the derailleur forward. Measuring cog wear is not easy but the 13T may be a bit too worn out to hold a brand new chain with lots of load on it. Some cassettes -cogs are very low hardness which wear out very quickly in some conditions.
 
I didnt notice what this is used with ... just pedal power ?, mid drive ?, hub motor ?...what max power ?
Whilst i admire you attention to detail, i doubt a link or two on chain length is the cause of your problem.
Do you have another chain to try ?.. or another cassett ?
Rather than assuming the problem is xxxx,...Use the “process of elimination” to focus in on the source issue,
 
another thing you could try is using a 9 speed chain to tighten things up. A lot of times this will solve problems that seem to have no other remedy
 
Slowly turn the crank with the bike in a stand or the rear wheel off the ground. If it’s a chain issue you should be able to pin point it because it will skip in the same place every time. If you have a master link check to make sure it’s completely locked. If it’s not it’ll skip on that link.
 
the aft gets around 1-2k km on a chain i no longer oil the chain on the cassette. I need to change cassette ,chain and long cage derailleur to have it reliable .slip seem much greater with lube .
i know when the chain replacement is due because the chain jumps between gears .
for me replacing only one of the three components wont stop the chain slip or jumping
https://www.cyclingdeal.com.au/buy/venzo-mtb-bicycle-c-guide-alloy-cnc-chain-guide/VZ-F22-003 .
this chain guide also on our other bikes is worth the money.
 
Letterman said:
There's no measurable wear on the chain (tried 2 different wear checkers, and measured with a ruler), however the chain has just started skipping on the 13T sprocket under heavy load.
Not sure if you knew this but you have to measure the chain while stretching it to get a valid measurement. IOW, crank on the pedal with the wheel on the ground to stretch the chain along the top, where you will measure. But hard to believe you have worn the chain very much in only 250km.

Also closely inspect the sprocket for any bent or damaged teeth.
 
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