How can I choose the right crank bolts for my Bosch Activeline motor?

halfer

Esteemed Pedelecer
I am need of new crank bolts, as I have had a number of bolts work their way loose, and am trying to work out what bolt I need. The plethora of options online is not making it easy, and I am not aware of any local shops that carry what I need (Halfords and Evans don't stock them, and aren't all that knowledgeable about e-bikes anyway).

My main commuter bike is a KTM Macina Action (2014) with the Bosch Activeline drive. My other bike is a Scott eGenius 730 (2017) with the Performance CX drive (and I mention that because I am able to swap crank bolts between the two).

I use Miranda crank arms and a mix of Miranda and non-Miranda bolts. These M15 bolts look correct:


However, there do not seem to be any size markings on the bolt I have left (just a Miranda part code, which is mostly unreadable). Some bolts seem to put the size in the key well, but this one does not.

I know that the bolt is not an M12, as I have that for my old Bosch Classic drive bike, and that one is definitely too small.

I have seen some M14 bolts online, as that is a size slightly bigger than the M12 that might plausibly fit. However this Miranda site does not list a M14, which leads me to think that the M15 is what I need:


I would happily measure my last bolt, but I am not sure what dimension the "M" refers to - anyone know?

These M15s also look suitable, and are sold in pairs. There is no mention of e-bikes or Bosch though:


They are also available in M14, which makes me cautious, in case that is what is required.

How can I narrow down what I need? (What would be great is technical model specification documentation from bike manufacturers, available even for historical models, but I don't think I have ever seen such material go into the level of detail that would be necessary in this case).

If any UK suppliers here carry what I need, feel free to link to your product page, or otherwise supply details. Thanks!
 

soundwave

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May 23, 2015
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why are they coming loose is the thread damaged and a loose fit so just come undone no matter how tight you do them up ?
 
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Deleted member 25121

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I would happily measure my last bolt, but I am not sure what dimension the "M" refers to - anyone know?
"M15" indicates that the bolt has a metric standard thread (the M) and has an outside diameter of 15mm (the 15). The other 2 variable are the length of the bolt and the type and size of the head.
 
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soundwave

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May 23, 2015
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this is what i have on my Miranda carbon cranks as did not come with any bolts even tho they cost £100 each.


they are self extracting so no need for a crank puller but you need a pin spanner or circlip plyres to install the black lock ring over the bolt in the crank arm and a bit of lock tight on that will make it never move again ;)

 

halfer

Esteemed Pedelecer
why are they coming loose is the thread damaged and a loose fit so just come undone no matter how tight you do them up ?
Good question. I seem to have lost at least two bolts recently (though I am down to one from two bikes, not sure how that happened :rolleyes:). Anyway, of the two I can account for, yes, the first did have a damaged thread. The second one seemed to be working its way loose, and since it was not reverse threaded (on the left hand side) pedaling had the effect of undoing it. Unfortunately I did not get my hands on some Loctite fast enough, and yesterday I arrived at a destination with that bolt missing.

So yes, when I get replacements, I will absolutely check the threads.
 

halfer

Esteemed Pedelecer
the bolt has a metric standard thread (the M) and has an outside diameter of 15mm (the 15)
Ooh, nice one - I think I have a tape measure, I will see whether I think my last bolt is a 14 or a 15.
 

halfer

Esteemed Pedelecer

soundwave

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May 23, 2015
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m15 is 15mm wide i checked it with my caliper on my spare crank bolts ;)
 
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soundwave

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May 23, 2015
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DSC_0162_01.JPG
;)
 

halfer

Esteemed Pedelecer
Thanks @ebiker99, @soundwave and @Wicky. I ordered the M15 bolts from Wiggle, they fitted both bikes perfectly. Nice to discover it's not an e-bike specific part.
 
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