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New chain bumps chain wheel / old chain wheel replacement?

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New chain bumps chain wheel / old chain wheel replacement?

Old 02-12-15, 12:23 PM
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KnOMTB
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New chain bumps chain wheel / old chain wheel replacement?

Hi, my name's Ian, I'm new here, so please forgive my ignorance(s) and thank you in advance for any advice you can give.

A little history of my bike before I get into it:
It's a 9 speed MTB, about 10 years old, I bought it second hand about 3 years ago when it was given some new parts such as cables and chain, but the cassette, derailers and chain wheels are all original parts (Deore LX). It's a Slovakian brand (Dema) - I live in the Czech Republic. I use my bike to commute daily, and winter conditions here are tough on parts, with all the salt and grit on the roads, so I try to keep the chain clean but inevitably there are days when I'll leave it. This wear and tear caused me to get it serviced a week ago as the chain had 'stretched' in the past three years of use - also, the shifting wasn't working well so I asked for my bike shop to sort it out - when I picked it up I noted the new rear derailer cable (much better shifting now, though it seems a bit short when referring to Sheldon Brown, RIP) and crucially a new SRAM chain (the previous one was Shimano). I asked the mechanic if I needed new chain wheels/cassettes but he said it wasn't necessary this time.



The problem:
When I am on the middle chain wheel and the smallest cog, the chain (the top run, under load) bumps into the small pins on the large chain wheel, which briefly lift the chain causing a noise:



I noticed earlier when trying to figure out why this was happening that the new chain says 8SPD on it:



Could this mean that the bike mechanic fitted the wrong chain? Do I need a chain for a 9 speed system or should this chain work just as well? It does seem to be a wider chain than the Shimano I had before. It does seem odd that a professional should make this mistake.


Additional question:
The middle chain wheel is the one I use about 90% of the time, and it does look quite worn. As I mentioned, the mechanic said I didn't need a new one - do you agree?



Lastly, if I were to replace the middle chain wheel myself (I didn't check but I'm pretty sure it's 32T), what do I need to check so I get the right one? It says it is a Mega Drive Chain Hollow-Tech unit.



While it looks very similar, the following I found on eBay has different looking cranks - are they inter-changeable?

Shimano DEORE LX M571 crankset | eBay


I also found this, which looks like it might fit but I'm not sure how to know:

Shimano Chainrings 104 64 BCD PCD 22 to 48T Chainring Chain Ring Grey Deore MTB | eBay

Thanks!
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Last edited by KnOMTB; 02-12-15 at 01:14 PM. Reason: edited for clarity
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Old 02-12-15, 12:46 PM
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There are two likely possibilities, maybe both working together. You weren't clear whether the problem was in the upper loop or lower, but I suspect it was the lower.

First of all, there's a difference in width between 9s and 8s chains:

  • 08 speed - 7.1mm (all brands)
  • 09 speed - 6.6 to 6.8mm (all brands) (from wikipedia)

So it's possible that the older, narrower chain just barely cleared the ring and the newer one's added width is just enough to make it touch.

The other possibility, and possible cure relates to the RD hanger. If it's not dead vertical, the lower pulley might be outboard more than the inner, so the chain in the lower loop is coming from farther out than the one in the upper. It's even possible that in the past the RD hanger was bent in a bit, so the lower pulley was inboard, and the shop did you the courtesy of checking and correcting it. This would apply if the chain touches on the lower loop but not the upper.

Test by applying a brake with a tightened string on the lever, then rotating the crank until a pin is at the chain and tensioning the chain. Eyeball for a gap, or try passing a piece of paper between the chain and pin. Try a few pins in case the ring is slightly warped and see if there's clearance on all of them. If the chain clears on top, but touches on the bottom, then it's likely the hanger.

So, you may need only a narrower chain, or maybe can solve it by tweaking the hanger or both.
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Last edited by FBinNY; 02-12-15 at 12:52 PM.
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Old 02-12-15, 12:56 PM
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One option to consider is to switch up to the big ring and use the equivalent ratio, instead of using the middle ring and smallest cog. This could potentially help your chain last longer too.

If the new chain isn't skipping on the middle ring, I wouldn't replace it yet.
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Old 02-12-15, 01:16 PM
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Thank you for the replies, I have edited the post to indicate that it's the top run of the chain which is lifted by the large chain wheel pins. I don't think the hanger is bent because before getting it serviced I was worried it was bent and asked them to straighten it in the shop, which they seem to have done (or didn't because it wasn't necessary, I forgot to ask).
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Old 02-12-15, 01:37 PM
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OK, that simplifies it. Since the old chain cleared the pins, and the new one doesn't, than the only variable is the chain width. A narrower chain will in all likelihood solve it. Also doublecheck that the chainrings aren't warped (wobble as they turn), since that's a contributing factor.

I agree, that it makes better sense to use the outer ring with a proportionately larger rear sprocket rather than the middle and outermost. But that doesn't mean you shouldn't have that option, especially for short term situational use. I'd go back to the dealer and ask why they fitted an 8s chain on your 9s bike.
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Old 02-12-15, 01:44 PM
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Perhaps : place some shim washers around the 4 bolts , between the chain rings ,, and the crank arm ..

that will spread out the distance between the 2 neighboring chainrings, depending on How thick the shim washers are..
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Old 02-12-15, 01:57 PM
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To answer another one of your questions, there are two types of cranksets. One has a JIS square tapered spindle that the arms mount on, and the other is called "octalink". They are totally different and will not interchange. Also measure your BCD, Bolt Circle Diameter to make sure you get a like chainring if you only change one chainring. Mountain bike chainrings are "usually" different than road bike chainrings and have different BCD and different number of mounting points on the spider, 4 verses 5. Yours are 4.
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Old 02-12-15, 02:47 PM
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I'm in the get the right chain consensus on this. Take the chain-width numbers with you to the shop.

I'm curious about the chainring warpage thing though. How do you cause that? Crash? Torching on a bottom bracket? It seems like a warped chainring, (or for that matter if the whole works were somehow out of "true" which would show the same symptom), should have audible differences in the sound heard as the crank rotates and the chain touches the big ring; chain contacts outer ring, then doesn't, then does again, as you pedal. Or maybe the noise is always present but alternates louder-softer-louder.
My $.02 from a non-tech.
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Old 02-12-15, 10:56 PM
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Originally Posted by tattman23 View Post
....

I'm curious about the chainring warpage thing though. How do you cause that?.....
They warp like old vinyl records if you leave them in the sun too long.

Seriously, they bend from abuse, like crashes or rough handling when you load the bike in a car. I use the word warped to describe gentle slight bends, and save bent for when they are beyond usable.
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Old 02-13-15, 05:35 AM
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On top of everything already mentioned, it appears the new chain may be a bit short. The rear derailleur is in a very forward position and the chain isn't on the big front ring yet.

As to your question about the rear derailleur cable loop. it appears to be on the short side also.
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Old 02-16-15, 12:38 PM
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Originally Posted by 02Giant View Post
On top of everything already mentioned, it appears the new chain may be a bit short. The rear derailleur is in a very forward position and the chain isn't on the big front ring yet.

As to your question about the rear derailleur cable loop. it appears to be on the short side also.
I thought it might have been. And I really find it annoying that they don't give the loop enough length, that's the second time out of three. The second time I got it serviced I specifically told them to make it longer than the current one, but this time I forgot.

So anyway I took it back and they admitted the mistake and put a 9SPD on instead - the noise seemed to have disappeared so I took it home. Because I don't have a bike stand, I do most work on the bike inverted (except washing and so on). When I got the bike home to have a proper look at it, I inverted it and the noise seemed to have returned, but it wasn't so bad, however when riding it it seems absolutely fine. Maybe it has something to do with the tension in the chain, but despite what everyone has been telling me about the middle chain wheel lasting another year or two, I do feel that it might need replacing already. The rings aren't warped though.

Thanks for the advice kwcahart.

As an aside, I've been reading lots of opinions on chain-tenance, and man is that topic controversial! I have no idea whether using solvents for cleaning is good or bad, whether using a chain bath (on-the-bike cleaning) is good or pointless, I don't know if I should be using teflon lube (it's pretty wet here in winter, but apparently 'everybody uses teflon these days'). So much to consider. I've settled on: get a chain bath for cleaning in winter (I use the bike a lot and constant grit and salt is a severe but unavoidable problem), use the thick silicon lube I bought in the bike shop for winter, and teflon in the summer when it's pretty dry here.
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Old 02-16-15, 12:48 PM
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IMO there's no real controversy about chain care. Just about everybody agrees that keeping a chain clean and well lubricated helps prolong it's life. There's disagreement about the "best" method of doing so, but the truth is that there is more than one way to skin this cat, and any of a variety of methods is effective if done properly.

Try various methods and settle on the one that work best for you, then do it well and you'll be fine.
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