Mountain Bike Reviews Forum banner

1 - 20 of 39 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1
It's fallen off 3 times now while riding. I have cleaned, regreased, and reinstalled it each time, but what is the problem? Nothing is stripped. It's the non drive size side. I bought the crank earlier in the summer and put about 500 miles on the crank so far.

I have sent a letter to Shimano 3 weeks ago, with no response so far. Any help/input is appreciated, thank you.
I have the same exact problem, My brand new shimano deore 12s crank keeps falling off, but the day before it was installed and double checked by Acme Bicycles, and then it fell right off again. So i put it back on, and i was riding dirt jumps that day, and the crank fell off up the lip of the gap jump, and it flung me over the bars face first into the landing.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #2
I have the same exact problem, My brand new shimano deore 12s crank keeps falling off, but the day before it was installed and double checked by Acme Bicycles, and then it fell right off again. So i put it back on, and i was riding dirt jumps that day, and the crank fell off up the lip of the gap jump, and it flung me over the bars face first into the landing.
I have decided to get a whole new crank set that is not shimano
 

·
Registered
Joined
·
1,022 Posts
I have the same exact problem, My brand new shimano deore 12s crank keeps falling off, but the day before it was installed and double checked by Acme Bicycles, and then it fell right off again. So i put it back on, and i was riding dirt jumps that day, and the crank fell off up the lip of the gap jump, and it flung me over the bars face first into the landing.
Do you have the little plastic shim installed in between the two halfs? That prevents the NDS crank to fall off even though it is lose. Do you torque it to spec? You can see that little spacer here

 

·
Registered
Ibis Ripley V4
Joined
·
281 Posts
I’m not trying to be argumentative, but this is something I would have to see to believe.

I have seen the Shimano crank interface hold with basically only the preload bolt and plastic shim holding the thing together.
 

·
Registered
Joined
·
3,230 Posts
I’m not trying to be argumentative, but this is something I would have to see to believe.

I have seen the Shimano crank interface hold with basically only the preload bolt and plastic shim holding the thing together.
I've seen it happen. I was riding down a flow/jump line behind a buddy and saw him riding with one foot off then saw his crank arm laying on the ground. He had prior issues with it coming loose though.
 

·
Registered
Joined
·
523 Posts
I have the same exact problem, My brand new shimano deore 12s crank keeps falling off, but the day before it was installed and double checked by Acme Bicycles, and then it fell right off again. So i put it back on, and i was riding dirt jumps that day, and the crank fell off up the lip of the gap jump, and it flung me over the bars face first into the landing.

Ummm......
 

·
Registered
Joined
·
3,564 Posts
My XT had that the plastic safety shim and torque plus loctitle, fell off 3 times. Last time I sustained injury. But it was my fault the initial install was not tight enough so the inside might have been a bit stripped.
 

·
Registered
Joined
·
241 Posts
My XT had that the plastic safety shim and torque plus loctitle, fell off 3 times. Last time I sustained injury. But it was my fault the initial install was not tight enough so the inside might have been a bit stripped.
Is it an XT M8120? Mine has always been torqued to spec, checked before every single ride, and nothing ever moved, but the NDS crank arm splines show some wear. I thought this was pretty weird considering the way I treated it, but maybe they have some issues with the alloy used in those 12 spd cranks.
 

·
Registered
Joined
·
3,564 Posts
Is it an XT M8120? Mine has always been torqued to spec, checked before every single ride, and nothing ever moved, but the NDS crank arm splines show some wear. I thought this was pretty weird considering the way I treated it, but maybe they have some issues with the alloy used in those 12 spd cranks.
M8000 series xt crank. 1x
 

·
Registered
Joined
·
7 Posts
Discussion Starter #10
I’m not trying to be argumentative, but this is something I would have to see to believe.

I have seen the Shimano crank interface hold with basically only the preload bolt and plastic shim holding the thing together.
Do you have the little plastic shim installed in between the two halfs? That prevents the NDS crank to fall off even though it is lose. Do you torque it to spec? You can see that little spacer here

i did have a shim/ crank lock on it, but it snapped it right off.
 

·
Registered
Joined
·
15 Posts
i did have a shim/ crank lock on it, but it snapped it right off.
i did have a shim/ crank lock on it, but it snapped it right off.
Just had the same thing happen to me with the new Deore 6100 crankset. Brand new bike and during the 6th ride the arm fell off with no warning. It can no longer be used due to spline damage. The preload nut nor the pin keeper were enough to keep the arm on. What concerns me most is that the interface only engages 8mm of lateral surface area on the spline. My older 11speed XT on my other bike had a much bigger engagement area. I now question the design.
 

·
Registered
Ibis Ripley V4
Joined
·
281 Posts
I'm going to have to pull my XT 8120 crank and check it out soon. I don't recall there being any less spline interface than the m8000 cranks I have installed many times.

I spent about a season on 175mm 8120 cranks (on my Niner Jet 9 RDO and Ibis Ripley V4) and then pulled them for 170mm 8120 cranks when I wanted more ground clearance with the Ripley. Both have been flawless for me.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #13
Just had the same thing happen to me with the new Deore 6100 crankset. Brand new bike and during the 6th ride the arm fell off with no warning. It can no longer be used due to spline damage. The preload nut nor the pin keeper were enough to keep the arm on. What concerns me most is that the interface only engages 8mm of lateral surface area on the spline. My older 11speed XT on my other bike had a much bigger engagement area. I now question the design.
I also agree and have noticed that.
 

·
Registered
Joined
·
15 Posts
How are the BB's and cranks spaced? What crank is it (6100,6120,6130)?
BB is 73mm BSA with one 2.5mm spacer on drive side. My understanding is the 6100, 6120 use the same spindle length - 115mm. Boost has different spacing on the chainring to get the proper chain line 52mm. Here is a pic of the interface.
1914273

The bike shop and Shimano are working on it and will take care of the issue. I have other Shimano cranks (11 speed XT) with the same design (non-boost) and have never had a problem but the difference is that they engage a bit more of the spline. The failure could also be a difference in material or annealing process. Hard to tell without subjecting the arm to lab testing. Nonetheless I never had a crank arm come off on me before. As stated earlier, the minimal engagement makes me nervous.
 

·
Registered
Ibis Ripley V4
Joined
·
281 Posts
That should be a boost crank on your Ibis (assuming based on your pictures).

For the crank there should be one 3mm spacer on the non-drive side crank arm, one 3mm spacer on the drive side. IF it’s actually a boost crank (xx20 series). ALL of the cranks require different spacers depending on the crank spacing. Non-boost, no crank spacers, boost is one 3mm left and right spacer, super boost is one 4.5mm left and right spacer.

Since your bike is a boost bike, you should have a Deore 6120 crank.



1914294
 

·
Registered
Joined
·
15 Posts
Thanks for the information, I had not seen the installation guide before as the bike came assembled. Yes correct, Ibis v4 Ripley. The right crank arm says FC6100 so it appears to be standard not boost. The left arm says FC6100/FC6120/FC6130 which fits all three. No spacer on the spindle either. Just one spacer on the bottom bracket side. That explains the lack of engagement mystery.

1914297
 

·
Registered
Ibis Ripley V4
Joined
·
281 Posts
Thanks for the information, I had not seen the installation guide before as the bike came assembled. Yes correct, Ibis v4 Ripley. The right crank arm says FC6100 so it appears to be standard not boost. The left arm says FC6100/FC6120/FC6130 which fits all three. No spacer on the spindle either. Just one spacer on the bottom bracket side. That explains the lack of engagement mystery.
The drive side BB spacer should be there. But are you sure there are NO spacers on the crankset spindle?

Drive side and non-drive side should NOT have a spacer for that crankset.

For Shimano to make the different cranks (standard, boost, super boost) they simply attach a longer spindle and use spacers to produce wider chainlines and Q factors. If ANY spacer is on your non-boost, standard spindle it will not allow enough purchase on the splines, creating your spacing issue. It almost looks like there is at least one spacer on that spindle.
 

·
Registered
Joined
·
40 Posts
BB is 73mm BSA with one 2.5mm spacer on drive side. My understanding is the 6100, 6120 use the same spindle length - 115mm. Boost has different spacing on the chainring to get the proper chain line 52mm. Here is a pic of the interface.
...
This thread caught my attention as I installed SLX M7100 crankset + MT800 BB couple months ago. It's been fine for the 10 or so rides so far. Mine's 73mm BB (19 stumpy). I have one 2.5mm spacer between the frame and drive side BB just as specified in Shimano's manual, and no other spacers for the cranks. Got curious and removed the crank screws and preload cap to see how the spline engagement looks on NDS (pic below).I'm thinking both 6100 and 7100 have the same spindle length. Also with the crank screws tightened the preload cap wouldn't budge; makes me think that would hold the cranks in place instead of the crank abruptly coming off without warning, but your experience is concerning.
Keep us updated; interested in knowing the outcome especially if they replace cranks. Hope yours gets sorted out soon 🤞

PXL_20210202_174638892.jpg
 

·
Registered
Joined
·
15 Posts
The drive side BB spacer should be there. But are you sure there are NO spacers on the crankset spindle?

Drive side and non-drive side should NOT have a spacer for that crankset.

For Shimano to make the different cranks (standard, boost, super boost) they simply attach a longer spindle and use spacers to produce wider chainlines and Q factors. If ANY spacer is on your non-boost, standard spindle it will not allow enough purchase on the splines, creating your spacing issue. It almost looks like there is at least one spacer on that spindle.
I am absolutely sure there is no spacer on either side of the crank spindle. The right arm butts up to bottom bracket bearing against the locking ring holding the chainring spider in place. The left side arm mounts directly to the spindle over the spline and also backs up to the bottom bracket bearing.
 
1 - 20 of 39 Posts
Top