DI2 9070 front shift issue??

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beanbiken
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by beanbiken

Ok, after some guidance. Sometimes [50/60%] when I go from the small chainring [36t] to the large CR [25t] the chain almost sits on top of the teeth until it is about 75% wrapped around the large CR then it drops into place. The rest of the time it engages 100% almost immediately. CR's are new Shimano OEM. Chain has been checked with a gauge and there is not noticeable wear. I don't recall this happening when the GS was fitted to my other frame, it was running a 53/39 CS. I have tried readjusting as per the manual and all I can think of, do I have a problem or that is just how it? Any thoughts or guidance much appreciated.

Thanks in advance, Steve.
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scamper996
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by scamper996

I had the same problem with 52,42 chain would just ride on top of the teath and sometimes jammed in between the rings. Ended up with bent rings. Also Shimano says diff must be 11 to 14 teeth only. Never happened on a 53/42 or 52/39.

Before I was on 7970 no problems with 52/42 but 9070 had all the problems above. Shimano Rep never gave me a good answer.

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beanbiken
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by beanbiken

scamper996 wrote:I had the same problem with 52,42 chain would just ride on top of the teath and sometimes jammed in between the rings. Ended up with bent rings. Also Shimano says diff must be 11 to 14 teeth only. Never happened on a 53/42 or 52/39.

Before I was on 7970 no problems with 52/42 but 9070 had all the problems above. Shimano Rep never gave me a good answer.

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Were you able to resolve it or are you just "living" with it?

Steve
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scamper996
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by scamper996

Never solved it, nearly damaged my frame when the chain got caught. On the bike stand everything was perfect but out riding when u dropped from 52 to 42 sometimes it would be OK sometimes float on top then engage, sometimes it jammed between. I gave up and went back to 52/39 with immediate zero issues. I didn't wan to risk it , it was so random. Sorry can't be of much help.

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beanbiken
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by beanbiken

Nah, no need to appologise, appreciate your input
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DeeHubbs
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by DeeHubbs

Shimano has 2 different 52 chair ring options, each are matched with their respective small rings. This means the 52 (for 39) and 52 (for 36) are different. The ramps and shift pins are specifically designed to shift at the right time onto the smaller chain ring. If you try to just swap out the small ring to change your gearing the original 52 will not shift well. It seems fine in the work stand, but once under load you will get the results that you experience.
Here is a GIF that shows the difference between a 52-39 and a 52-36.

Delorre
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by Delorre

DeeHubbs wrote:Shimano has 2 different 52 chair ring options, each are matched with their respective small rings. This means the 52 (for 39) and 52 (for 36) are different. The ramps and shift pins are specifically designed to shift at the right time onto the smaller chain ring. If you try to just swap out the small ring to change your gearing the original 52 will not shift well. It seems fine in the work stand, but once under load you will get the results that you experience.
Here is a GIF that shows the difference between a 52-39 and a 52-36.


Completely right! I was planning on using a 39t inner instead of 34 on my 9070, but the mechanic told me not to do it, because of the inner shape of the outer ring, that is designed specificly for a given inner ring. With 50 - 39, the chain would jam between both he told me. 50 - 36 works for 99%. BUT, is beanbiking using a stock 52 -36 or has he changed the inner from 39 to 36 and run into trouble after that?

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toiyuet
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by toiyuet

For your reference :

9000 - 複製.jpg

mattr
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by mattr

FWIW there are two issues here, internal ring profile and clocking if the two rings, they are arranged so that the chain will drop (or climb) into the right position during the shift, allowing it to be properly engaged on both rings.
If you get the wrong clock angle, it'll not engage cleanly and may skate over the teeth.

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Calnago
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by Calnago

Exactly, you always get people saying odd combinations work fine, but really they don't. At least not perfectly, all the time. That's a good as explanation as any given by Mattr above as to why the "timing" of the rings is specific to certain combinations. Mix them up and things can get funky.
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mattr
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by mattr

It's not my explanation, it's shimanos. It was a long time ago, but i think it may have coincided with the launch of the letter specification chain rings.

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Calnago
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by Calnago

Well, whosever explanation it is, it's correct. There's a reason they pair certain rings with each other and doing otherwise may be workable but not optimal. I know I've done things in the past that weren't "factory recommended" but I did so knowing full well what the limitations were and accepted the tradeoffs.
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beanbiken
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by beanbiken

Ok guys thanks for your thoughts. Yes it is a factory crank & rings and I have already checked the rings alignment as per Shimano. Thinking I may swap back to my 53/35 crank and see if the issue resolves itself. Wondering if the chain has a V/small amount of wear [likely] which is affecting the interface between the new rings and the not-that-old chain. If the change of crank sorts it I have a brand new Shimano chain in reserve which I will try. Damn frustrating
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