Inmotion v12 Pedal Snap

[Punxatawneyjoe]

12 minutes ago, zer0dayexploit said:

I’m just proposing potential reasons for why a bolt grade that is much higher may not be a good idea.

I would agree with this, especially when its to hold a pedal hanger that takes a ton of vibration and shear force. A stronger bolt is more "brittle" to shock forces wheres a softer bolt can absorb the shock before shearing. You would think the stronger the bolt the better for holding the weight and that would be true but the harder the bolt the more susceptible to cracking with the shock force. I am no steel expert either but this is the way i have understood it over the years.

[Planemo]

16 minutes ago, zer0dayexploit said:

Another concern is if the bolt is of a much stronger steel than the thread it mounts into, that it ends up stripping the mount threads.

In this EUC case the bolt hole will always strip first whatever bolt you put into it because the bolt is steel and the hole is alloy...

...unless one is using utterly shite steel bolts that are even weaker than the aluminium they are threaded into.

[Planemo]

Just now, Punxatawneyjoe said:

I would agree with this, especially when its to hold a pedal hanger that takes a ton of vibration and shear force. A stronger bolt is more "brittle" to shock forces wheres a softer bolt can absorb the shock before shearing. You would think the stronger the bolt the better for holding the weight and that would be true but the harder the bolt the more susceptible to cracking with the shock force. I am no steel expert either but this is the way i have understood it over the years.

Yes the theory is all correct but we're talking 10.9/12.9 steel bolts. Four of them no less. On an EUC. This isn't industrial grade heavy machinery.

Find out what bolt diameter this installation uses and you can easily look up the sheer and tensile strength of the bolts. I promise you 110% that a human on an EUC will have no chance of sheering/bending either spec, even with the added brittleness of a high tensile steel.

But people can fit whatever they want, go back to chinesium 'specially formulated pasta steel with added flexibility' if you like.

It's funny because to me it seems the original ungraded bolts were too brittle...

[Rawnei]

I would definitely go with 12.9, same as I did with motor bolts on my wheels.

[zer0dayexploit]

@Planemohaha no ways will I go back to inmotion’s bolts. It appears that they are a fake grade 10.9 or 12.9. Went today to buy some from a reputable bolt manufacturer nearby, and it’s interesting how identical visually inmotion’s pedal bolts are. Inmotions factory bolts definitely aren’t up to spec but whatever company is supplying them did a good job hiding it

[Planemo]

Do the stock bolts actually have a marking on them then?!

[techyiam]

30 minutes ago, zer0dayexploit said:

Inmotions factory bolts definitely aren’t up to spec but whatever company is supplying them did a good job hiding it

Those four bolts on each side, for the adjustable pedal block are soft. I and others can confirm that. And it is not an outlier thing. Inmotion were supplied with substandard bolts. However, those are the only bolts I found below par on my V12.

[Planemo]

Inmo should be shipping out proper bolts to every affected wheel and advising riders to not use the wheel until replaced IMO. Way too dangerous. This isn't a 'minor' issue.

[zer0dayexploit]

46 minutes ago, Planemo said:

Do the stock bolts actually have a marking on them then?!

Yeah they have the 12.9 grade marking and everything.

[Planemo]

2 minutes ago, zer0dayexploit said:

Yeah they have the 12.9 grade marking and everything.

Jeez!! Thats properly naughty! No way on earth that is a genuine 12.9 bolt. Is nothing fake in China? I never would have thought you could buy fake rated bolts 

[zer0dayexploit]

I’ll try upload some helpful tips and advice and info on the bolts, extraction tools etc once I’ve got my wheel all back together for anybody else this might happen to. But yeah this sucks. Extraction was kinda tricky but the hangers and threads are left untouched.
 

Interesting thing I’ve noticed is that the bolts also seem quite short for the amount of thread space provided. The factory bolts are about 14mm but there’s definitely some space for a 16mm or even an 18mm so the loctite has some extra surface area. I’ve seen many people reporting their bolts slowly walking out on them.

[Planemo]

Yeah go as long as you can. Whilst we are on the subject I recently had to source some new Loctite, I found a really good product they make, 248. It's like the well known blue 242 but it's in a stick. Less messy, easy to use and a better shelf life too. £6.50 and worth every penny

 

[zer0dayexploit]

@Planemohaha yeah I use that one too! It smells really good for some reason  

[Frolic0415]

On 8/30/2023 at 5:20 PM, Rawnei said:

Just go with 12.9 if you are buying replacements yourself?

What size is the bolt? I'm going to get 12.9 grade but not sure the size/name of the exact bolts I need.

[Hellkitten]

4 minutes ago, Frolic0415 said:

What size is the bolt? I'm going to get 12.9 grade but not sure the size/name of the exact bolts I need.

You could always take a bolt from the opposite hanger and bring it to a hardware store or measure it. 

[Eucner]

4 hours ago, Frolic0415 said:

I'm going to get 12.9 grade

Class 12.9 is not specified for impact strength, 10.9 is.

[Rawnei]

2 hours ago, Eucner said:

Class 12.9 is not specified for impact strength, 10.9 is.

Where did you get this information? What do you mean by impact strength?

From all I can read 12.9 is stronger in every way:

https://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx

[Eucner]

3 hours ago, Rawnei said:

Where did you get this information?

ISO 898-1:2013 Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1: Bolts, screws and studs with specified property classes — Coarse thread and fine pitch thread, Table 3, Value for Kv is under investigation.

For classes 5.6, 8.8, 9.8 and 10.9 the impact strength value is 27 J. In the year 1999 version of standard impact strength values were: class 5.6 25 J, class 8.8 30 J, class 10.9 20 J and class 12.9 15 J. Many manufacturers still use these old values.

3 hours ago, Rawnei said:

What do you mean by impact strength?

ISO 148-1:2016 Metallic materials — Charpy pendulum impact test — Part 1: Test method

Values are determined at a test temperature of −20 °C. This might not be as meaningful in Australia as it is in Sweden.

[Rawnei]

2 minutes ago, Eucner said:

ISO 898-1:2013 Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1: Bolts, screws and studs with specified property classes — Coarse thread and fine pitch thread, Table 3, Value for Kv is under investigation.

For classes 5.6, 8.8, 9.8 and 10.9 the impact strength value is 27 J. In the year 1999 version of standard impact strength values were: class 5.6 25 J, class 8.8 30 J, class 10.9 20 J and class 12.9 15 J. Many manufacturers still use these old values.

ISO 148-1:2016 Metallic materials — Charpy pendulum impact test — Part 1: Test method

Values are determined at a test temperature of −20 °C. This might not be as meaningful in Australia as it is in Sweden.

Seems like you are just pasting random text? Please cite sources and your reasoning why you think any of that it makes any difference in this case.

[Eucner]

2 hours ago, Rawnei said:

Seems like you are just pasting random text?

Quite opposite. They were exact answers to your questions. Standards are commercial. I won't post them here, although many parts of them are easily found with Google search. I need to ask you to do it yourself.

Yield strength is important for bolt tightening. Fatigue strength is important for durability. Impact strength is important for, especially low temperature, impacts like pedal clipping. When also considering hydrogen embrittlement, in this case I wouldn't choose higher class than 10.9.

Edited September 5, 2023 by Eucner

[alcatraz]

Why is impact strength relevant here? Tensile or shear strength seem appropriate to maximize.

Does it have to do with vibrations? Brittle vs flexible? Movement is usually bad because it'll fatigue.

Impact strength seems like something you'd want when making armor.

Edited September 6, 2023 by alcatraz

[Punxatawneyjoe]

56 minutes ago, alcatraz said:

Why is impact strength relevant here?

From what I've seen the EUC "mechanic" community "loves" the cordless impact gun. Even the "pro's" at shops use them. And when someone says "i checked the bolts recently" That usually means a couple of quick pops with the impact gun. And usually , the harder the bolt. The less it enjoys repeated shocking blows, usually greater than it's intended torque specs. Although brief, they can accumulate hair line fractures in the bolt weakening it. Not saying that's what happened here, but it could explain such a catastrophic failure on a crucial piece. Not ruling out improperly marked bolts from China either, because they even fake eggs. But without a rockwell test, you are out of luck proving it.

[Eucner]

5 hours ago, alcatraz said:

Why is impact strength relevant here?

Impact strength is a measure of brittleness.

[alcatraz]

Ok.

Have you guys determined if the bolts snapped because of being too brittle OR from inadequate tensile strength?

Seems like an important question.

[Eucner]

13 minutes ago, alcatraz said:

Have you guys determined if the bolts snapped because of being too brittle OR from inadequate tensile strength?

My bet is on loose bolts. It will increase significantly the dynamic load on bolts and lead to growing fatigue crack as seen in the photo. Finally bolts will suddenly fail. Fake bolts may also play a part.