Premature jockey wheel wear
Discussion
I fitted a rear mech to my mates bike just after Xmas and already his rear jockey wheel looks like this.
What could have caused this wear? I had to size the chain as the mech I fitted had a longer cage that the one it replaced. Could the chain be too tight or too loose?
Thanks in advance!
Edited to add that I know it could do with a clean!
What could have caused this wear? I had to size the chain as the mech I fitted had a longer cage that the one it replaced. Could the chain be too tight or too loose?
Thanks in advance!
Edited to add that I know it could do with a clean!
CubanPete said:
Looking at where the chain enters at the top it doesn't look very well aligned.
Assuming we hasn't dropped it, it was a brand new mech fitted to a brand new hanger (the previous unit snapped off the hanger) so everything should be straight. Do you think I should take a link out the chain to increase the tension?
Chain stretch and chain length are not the same thing. Chain stretch occurs when each link and each roller in the link wears a tiny bit and makes each individual link a tiny weeny bit longer, over the length of the chain this adds up to a longer chain, but importantly each link has a pitch which is now longer than the tooth it's designed to engage into thus causing improper engagement and wear on the tooth. Over the length of the chain it will add up to a measurably longer chain but just taking a link off the end to make it the "correct" length doesn't fix the problem of each link not fitting the tooth. To measure chain stretch you really need a chain wear gauge which will tell you when its exceeded 0.7% or 0.5% which are the limits for replacement depending on the speed of the cassette. (anything 10sp and up being 0.5%, 9sp or below being 0.7%) you can do it with a ruler over a decent length of chain but not ideal as you have to remove the chain and then get an accurate measurement with the chain under some tension but google is you friend on how to do it.
As for jockey wheels, they don't have the full tooth profile of a cassette or chain ring, but are half tooth's, Yours don't look too far from the norm but its hard to tell if the spots that look odd are because of the gunge or wear. You really need to clean it up properly and get all the gunk lip off that forms at the perimeter of chain engagement at the bottom of the tooth to see if its wear or gunk.
You also need to figure out why the chain is not engaged at the top of the picture, it might be the chain is too long and not under tension so when the bike is on its side it just falls off or it might be just cross chaining and laying the bike down, but the things i think you need to do are.
1) clean it and determine if it really is worn.
2) measure chain stretch and if ok
3) measure the correct chain length
4) is it working properly or is there some other engagement issue causing the incorrect engagement in the picture. (are the jockey wheel bushings worn etc)
When you fitted it how did you measure chain length for the new cage. Cliff notes, big cog to big chain ring bypassing the derailleur, pulled tight and engaged, line up the plates that can be joined and add two rivets to find the cut point, but read and follow this https://www.parktool.com/blog/repair-help/chain-le... Just don't do it to shorten a worn chain.
As for jockey wheels, they don't have the full tooth profile of a cassette or chain ring, but are half tooth's, Yours don't look too far from the norm but its hard to tell if the spots that look odd are because of the gunge or wear. You really need to clean it up properly and get all the gunk lip off that forms at the perimeter of chain engagement at the bottom of the tooth to see if its wear or gunk.
You also need to figure out why the chain is not engaged at the top of the picture, it might be the chain is too long and not under tension so when the bike is on its side it just falls off or it might be just cross chaining and laying the bike down, but the things i think you need to do are.
1) clean it and determine if it really is worn.
2) measure chain stretch and if ok
3) measure the correct chain length
4) is it working properly or is there some other engagement issue causing the incorrect engagement in the picture. (are the jockey wheel bushings worn etc)
When you fitted it how did you measure chain length for the new cage. Cliff notes, big cog to big chain ring bypassing the derailleur, pulled tight and engaged, line up the plates that can be joined and add two rivets to find the cut point, but read and follow this https://www.parktool.com/blog/repair-help/chain-le... Just don't do it to shorten a worn chain.
As I understand it the overall chain length doesn't change as stated above, that is impossible and the metal links would have to elongate for this to happen.
As also stated above, Chain 'stretch' is the name given to the wearing of the small 'rollers', which are the contact point on the cassette, chain rings and jockey wheels. As these wear and get minutely smaller it alters how they contact each tooth on the rings etc in slightly the wrong place, which causes them to wear and in most cases become sharp. So the chain doesn't get longer, but the point between each roller does get bigger.
As also stated above, Chain 'stretch' is the name given to the wearing of the small 'rollers', which are the contact point on the cassette, chain rings and jockey wheels. As these wear and get minutely smaller it alters how they contact each tooth on the rings etc in slightly the wrong place, which causes them to wear and in most cases become sharp. So the chain doesn't get longer, but the point between each roller does get bigger.
Edited by SouthHamsGaz on Saturday 21st March 20:16
Thanks to everyone’s answers. Hiwever, understand chain stretch. I have a chain tool to measure the wear on a chain.
My comment on taking a link out of the chai wasn’t to correct chain stretch, it was in case The chain I fitted was too long and so wasn’t correctly tensioned, meaning that it was slipping on the bottom jockey wheel, wearing out the teeth.
Spare wheels ordered and I’ll clean and check the chain. And ask my friend (whose bike it is), to stop cross shifting!
My comment on taking a link out of the chai wasn’t to correct chain stretch, it was in case The chain I fitted was too long and so wasn’t correctly tensioned, meaning that it was slipping on the bottom jockey wheel, wearing out the teeth.
Spare wheels ordered and I’ll clean and check the chain. And ask my friend (whose bike it is), to stop cross shifting!
Mtb or road? Distance?
Possibly just a poor set.
My first set on my 105 wore out fairly quick just like that, 2k km max before the chain was slipping off the side of the bottom pulley. Next set lasted 7k km before one snapped in half from standing start just as I was collecting a new groupset.
Same setup (105) on my mates bike lasted 18k km! before he changed including running a chain well overdue to the point of snapping it!
Possibly just a poor set.
My first set on my 105 wore out fairly quick just like that, 2k km max before the chain was slipping off the side of the bottom pulley. Next set lasted 7k km before one snapped in half from standing start just as I was collecting a new groupset.
Same setup (105) on my mates bike lasted 18k km! before he changed including running a chain well overdue to the point of snapping it!
I don't cross chain, summer bike since '18 so doesn't see a dirty chain really. I changed them as a matter of good practice on my winter bike for under a tenner after 8k km of absolute filth riding through farms and stuff, they looked the same as the new pair but dirty!
Could always get some blinging hope ones!
Could always get some blinging hope ones!
My guess is that the chain is too short, and when in big ring to big ring, there is a side load on the lower jockey wheel.
If the mechanism is at the limit of its travel, then the chain is too tight and is applying a force to the jockey wheel and the more it wears, the further across the chain is running.
Should take a few seconds to check if the chain is too short by shifting to the biggest rings and checking if the mech is at the end of its travel.
Some jockey wheels are directional, upper and lower are reversed SRAM so be aware when you fit the new ones
If the mechanism is at the limit of its travel, then the chain is too tight and is applying a force to the jockey wheel and the more it wears, the further across the chain is running.
Should take a few seconds to check if the chain is too short by shifting to the biggest rings and checking if the mech is at the end of its travel.
Some jockey wheels are directional, upper and lower are reversed SRAM so be aware when you fit the new ones
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