FAILURE Shimano Cranksets

Discuss light weight issues concerning road bikes & parts.

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robertbb
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by robertbb

Perhaps the spider is forged, and the only bonded bit is the arm.... still though, bonded.

The seam is there, it's just on the underside, not the inside. Do you have that seam on your crank?

by Weenie


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pdlpsher1
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by pdlpsher1

Interesting. Since R7000 has a higher weight target perhaps Shimano used casting to make the crank as opposed to forging the crank in two separate pieces and then gluing the pieces together. I believe casting can be done to make a hollow structutre but it requires thicker walls to compensate for the lack of strength compared to forging. It would be interesting to see what Shimano will do on the new Dura Ace 9200.

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Stefano
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by Stefano

They absolutely would not cast a crank- too much porosity.

Hollow forging is when they use a steel mandrel in a set of progressive dies- keeping the inside hollow as they form the arms around it; and in the last step they remove the steel mandrel and smush the open end (pedal spindle) together.

The trend toward bonded is likely because you can get better control of the wall thickness by forming the clamshells separately- letting them drop the overall thickness and therefore weight. However it likely involves post machining + surface treatment ($) on the bonding surfaces, hence why the 105 cranks are designed for less total bonded area.

Thanks,
Stefano

robertbb
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by robertbb

I reckon Stefano is bang on the money here. That R7000 crank has less bonded area, not zero bonded area.

Whether that has resulted in a more robust crank, I guess time alone can tell because R7000 hasn't been around as long as the other lines. I'm not filled with confidence because there have been failures of the other cranks towards the pedal opening - not just at the spider. The R7000 looks as though it's still prone to similar.

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pdlpsher1
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by pdlpsher1

Shimano could also develop a robotic laser welding technique to join the two pieces together. Then use machining to smooth the welded area. With the right process the crank can be made very light, strong, and reliable.

With that being said I'm currently riding a Shimano group but with a Quarq PM. When the new 9200 comes out I still plan to stick with Quarq because I don't trust Shimano PMs.

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pdlpsher1
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by pdlpsher1

Here's a look at Shimano's latest 12-speed XTR crank. You can see the glue line just like on the Dura Ace. But interstingly Shimano also has a cheaper version of the XTR 12-speed crank and that one looks like the R7000 cranks with no visible glue lines. So it appears that Shimano is not abandoning the gluing process anytime soon.

Image

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robertbb
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by robertbb

Check if the glue lines are on the under side of the cranks... not the inside.

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pdlpsher1
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by pdlpsher1

No lines that I can see. But interestingly if Shimano is going to direct mount chainrings it does appear to eliminate a source of possible failure. In many failed Shimano cranks the outer piece of the crank comes apart at the spider.

Image

2lo8
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by 2lo8

I don't have any R7000 except the RD I purchased to see if it was plastic. Ever since the UK vendors no longer sell to the US, I haven't bought any Shimano groups, so I can't confirm anything about the R7000 cranks. I also loathe the fact that Shimano wants to use incompatible chainrings every new generation and tier, even if BCD is the same. I got rid of my 4 arm cranks since Shimano won't make it a "real" standard.

First, cranks can absolutely be cast, and absolutely are and were cast. You had many many decades of vintage cast and "melt forged" cranks which were actually cast. Don't ask me how they could legally advertise cast as "melt forged" but they could. Cast cranks are still being made today. Off the top of my head, FSA Tempo and Omega cranks are cast. Some(most?) Shimano Hollowtech were cast hollow, then had the pedal eye forged shut, so technically forged. Maybe some other methods, there's multiple patents, but casting comes up a lot. It's in a Shimano patent somewhere that I dug up once. Maybe some were fully forged, or maybe the castings were forged, I'm not priviy to Shimano trade secrets.

Second, I am pretty sure Shimano has no intention of making welded hollowtech cranks in the forseeable future. The first round of hollowtech was this way, and it was quickly changed and the old part phased out. Expensive, unreliable, reject rate, difficult QC, all of the above, your guess is as good as mine, but I doubt Shimano wants to seriously pursue it, they tried it once before and abandoned it as soon as they found an alternative method.

Third, I am skeptical that hollow forged is cheaper than bonded unless it's because they have lots of legacy tooling and machinery. Shimano has mixed cost cutting with design changes for recent components to increase margins. They improve performance with new designs, but cheap out on manufacture. If they made the same old designs with the new materials and methods of manufacture, it would come across as cheaper and worse (it's still good stuff, I'm just grouchy that the gradual material trickle-down over time have reversed). The outer shell of bonded cranks is just a stamping/pressing made from aluminum sheet even on DA. Cold(warm) forging is highly dimentionally accurate. That being said, it is likely that Shimano still owns expensive forging machines and maybe the marginal cost is cheaper than setting up new production lines (robots) for bonding.

If Shimano is still making non-bonded cranks, I think that's a good thing.
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ooo
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by ooo

Hollow cranks with glueline produced in Japan only (Dura-Ace,Ultegra;XTR):
2017-06 IFCR8000CX26
2013-06 IFC6800CX26

Hollow cranks without glueline produced in Japan (RX810,105;Saint,XT,SLX) and since 2017 also produced Malaysia (Deore M6000,T6010):
2019-05 IFCRX8102CX81
2018-04 IFCR7000CX26L
2014-06 IFC5800CX26L

2019-08 IFCM71002CX66
2016-03 IFCM7000CX66
2015-06 IFCMT700CX66

2017-06 EFCT6010CX866CL
2017-05 EFCM6000CX66X

Previously, Shimano Malaysia also produced Octalink/Square Deore hollow cranks without glueline:
2007-08 FC-M521 - Malaysia
2005-10 FC-M530 - Malaysia
2004-07 FC-M460 - Malaysia
2004-07 FC-M470 - Malaysia
2004-07 FC-M540 - Malaysia
2000-12 FC-M480 - Japan
1999-10 FC-M510 - Japan
'

schlafen
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by schlafen

https://www.youtube.com/watch?v=Vmp2G7zIby4&t=29s

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2lo8
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by 2lo8

Yeah no, Shimano uses some special epoxy that isn't just JB weld, connects a vaccuum pump to the crank to pull the epoxy through, then sticks them in an oven to cure. If Shimano can't get it right, I wouldn't count on getting it right by just slathering some JB weld on it. Better to not waste time or risk injury and just cough up the $150 for a 105 replacement crank and move the PM over.
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schlafen
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by schlafen

People used to drill the sh1t out of their bikes for the past 50 years, I'm sure it will be just fine. It's a bicycle.

There are bonding agents, available on the market, used in automotive manufacturing, yes, some cars use panel bonding besides welding in structral areas.
The metal surrounding the bonded area usually breaks first before the bond gives up.
Shimano should probably look into that.

However, in his case it split at the seam, the rest I've seen broken in this thread were not so lucky.

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2lo8
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by 2lo8

Drillium is taking an overbuilt part, lightening it, not riding it much or at least not on the training bike, and not being surprised it breaks if it does. If done right, it's material removed in low stress areas, rather than removing material in high stress areas already prone to failure. This is taking a part that has failed, and attempting a fix that is worse than the factory method which already failed, and expecting the inferior fix to work better.

There is no way in which these two things are comparable, even if Shimano screwed up big time. It being a bicycle has nothing to do with whether or not failures happen, as evidenced by the fact that these cranks are on bicycles, and also fail, meaning it being a bicycle didn't prevent them from failing the first time.

Neither is a logical argument for JB welding cranks back together.
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by Weenie


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pdlpsher1
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by pdlpsher1

This video popped up on my YouTube recommended video list, lol. Poor guy. Two broken cranks in two years. Hopefully Shimano is watching this and will take notice.

https://www.youtube.com/watch?v=KhXuEcJfEkI

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