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Discussion Starter · #1 ·
I've just put together a new bike using Shimano XT M785 cranks with 34t chainring, a 10 speed 11-36 rear cassette, X0 short cage derailleur and X0 grip shift, KNC chain. I've also put a Superstar chain guide on it as well, repalcing the very inner crank spacer with the aluminimum plate of the chain guide.

Setting it up and it shifts fine, no problem.

The issue I have is when you put it on the lowest gear (biggest cog) the chain instantly jumps off the front chainring.

Any ideas?!
 

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Discussion Starter · #3 ·
I need to check the chain line, but I thought as the bracket was the same width as the spcaer then the chainline should be unaffected. Could be though, as the chain always jumps to the inside. Having said that if I remove the spacer between the chain guide and the external bracket it would put the chain guide out I expect.
 

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The big ring position on 2x cranksets is not very close to a centered chainline on most frames, I can't remember exactly but I seem to remember it being somewhere around 5-7mm outboard.

Is the chainring non-ramped? All the drivetrain components new?
 

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Discussion Starter · #5 ·
The big ring position on 2x cranksets is not very close to a centered chainline on most frames, I can't remember exactly but I seem to remember it being somewhere around 5-7mm outboard.

Is the chainring non-ramped? All the drivetrain components new?
I actually think it might be a ramped chainring as it has steel pins, does that make a difference? All parts are new though.
 

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I actually think it might be a ramped chainring as it has steel pins, does that make a difference? All parts are new though.
You shouldn't actually need it since you have a chain guide but a non-ramped (ss) chainring is still preferable IMO. I would measure your chainline, use the search here or google it and you will find several easy methods that only take a few minutes. I have a feeling you are going to need to move the front chainring over a little.

If you get a different chainring you might want to consider getting a higher profile or narrow wide one (Race Face/ Wolftooth, etc.) and ditch the chain guide altogether.
 

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I ride a Swarf
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I would suggest a SS or thick thin ring, on my hardtail I have a thick thin (wolf tooth) with a clutch rear mech, no guide and my chain has come off once in the last 4 months or so of running this setup. Full suss may be more problematic though due to the extra movements.
 

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NedwannaB
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I actually think it might be a ramped chainring as it has steel pins, does that make a difference? All parts are new though.
Yes, that 2x crank set does not offer the optimum 1x chain line. And def do not want ramp/pinned "shift" ring on a single setup. The varying height profile of the teeth will want to carry chain off to inside, especially while you are granny "cross-chained" in the big cassette cog.
 

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Discussion Starter · #9 ·
Yes, that 2x crank set does not offer the optimum 1x chain line. And def do not want ramp/pinned "shift" ring on a single setup. The varying height profile of the teeth will want to carry chain off to inside, especially while you are granny "cross-chained" in the big cassette cog.
Thanks for the replies guys! OK - first off, it was a 780 crank, so 3 ring originally, and the chainring is currenty a 32t, not 34t! I measured the chainline at 51mm. I can adjust it over 4-5mm no problem, which would give me about 47mm.

If I do this and use a thick/thin chainring do you think thay should solve the issue?

Also. does the chainring size have any impact on chain retention? ie would a 34t retain it better than a 32t?
 

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This could be a really simple issue. Is the "Missing Link"/ Power Link pulled completely tight? I.e. pins engaged fully in the slots?

When I was putting on a new SRAM chain the other day I thought I had the link engaged completely but it wasn't fully in by ~2mm. Every time the link tried to mesh with the chainring it immediately jumped off. I used some pliers to engage the link all the way and no more issues. Effectively what happens is one link on the chain is shorter than all of the others and my narrow-wide ring didn't like it.
 
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Thanks for the replies guys! OK - first off, it was a 780 crank, so 3 ring originally, and the chainring is currently a 32t, not 34t! I measured the chainline at 51mm. I can adjust it over 4-5mm no problem, which would give me about 47mm.

If I do this and use a thick/thin chainring do you think that should solve the issue?
yes remove the ramped ring and replace with a NW along with moving it inward will solve the issue.

Also, does the chainring size have any impact on chain retention? ie would a 34t retain it better than a 32t?
Given you have converted a triple to 1x10 it may well be the chain requires 2 links removed to aid this.
 

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NedwannaB
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Thanks for the replies guys! OK - first off, it was a 780 crank, so 3 ring originally
That's good. Typically these 3x convert way better than the 2x so your set. Possibly without having to adjust your chain line.

Also. does the chainring size have any impact on chain retention? ie would a 34t retain it better than a 32t?
Shouldn't have an affect with either size using a narrow wide. As for front ring tooth count, depending on how much you used the cluster of rings before (i.e. more granny/middle-more middle/big), you may find you can run a 34t (or 36t depending on your fitness/terrain) when going to a 1x. This way you can retain some top end too lost by ditching the big ring.

As for chain length, could be only a couple lengths as mentioned. Typically wrap big-big and add 2 lengths, but may have to be adjusted for travel on some suspension designs.
 

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Discussion Starter · #13 ·
Have ordered a Race Face NW and will fit that to see how it goes. Given that I have some adjustment I may as well centralise it a little further. I expect I spend most of my time in gears 3-8.

I used an online tool for chain length as fitted a new chain, but will check that against the method suggested above. Given it's a hardtail I imagine that makes the job easier!

Thanks for your help guys!
 

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Discussion Starter · #14 ·
This could be a really simple issue. Is the "Missing Link"/ Power Link pulled completely tight? I.e. pins engaged fully in the slots?

When I was putting on a new SRAM chain the other day I thought I had the link engaged completely but it wasn't fully in by ~2mm. Every time the link tried to mesh with the chainring it immediately jumped off. I used some pliers to engage the link all the way and no more issues. Effectively what happens is one link on the chain is shorter than all of the others and my narrow-wide ring didn't like it.
Hi, I cheked this when fitting, as it was certainly tight snapping together!
 
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