Loose crank bosch ebike

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toerag69

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hi,

My left crank keeps coming loose. I tighten with 8mm Allen key and crank feels fine but after a few miles it goes loose.

Unsure if my spline, crank arms are OK or not in pictures.

Also does anyone now if there is a correct torque spec for crank arm bolts, just incase I'm not using correct amount torque.

Bike is cube stereo 160 bosch motor.

Thanks

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toerag69 said:
hi,

My left crank keeps coming loose. I tighten with 8mm Allen key and crank feels fine but after a few miles it goes loose.

Unsure if my spline, crank arms are OK or not in pictures.

Also does anyone now if there is a correct torque spec for crank arm bolts, just incase I'm not using correct amount torque.

Bike is cube stereo 160 bosch motor.

Thanks

View attachment 185117View attachment 185118View attachment 185119
Click to expand...
High Rock Ruti

My E13's had to be replaced with another brand. They stripped out, E13 on my brand new Orbea Wild Team Ltd. E13 refused to honor warranty, after buying 3 times, I gave up! I used Race Face, I think and the reason I not sure is, I've never had any cranks loosen ever, since the E13 POS.

Warm Regards Ruti
 
irie said:
Use Loctite 243

But use for example Loctite 243 so you can later undo the the bolt if necessary. Some stud lockers are very difficult to undo (they are designed to be so).
Click to expand...
Yeah the blue one
 
I know someone personally who has this same issue with Ethirteen cranks. They warranteed a new arm. Not sure if he’s had the issue since then. Previous to the replacement, it didn’t matter what he did, he could never get the arm to stay tight.
 
I am not saying that @Funkeydunk is wrong, but 50-60Nm is a seriously high amount of torque for an mtb! For reference 40Nm is typical for clamping the cassette. (About 35 lbs on a 10" long spanner).
Before going that high on torque, I would try the Loctite Blue route first.
If it doesn't work you can always try a higher torque (+Loctite Blue) later.
 
steve_sordy said:
I am not saying that @Funkeydunk is wrong, but 50-60Nm is a seriously high amount of torque for an mtb! For reference 40Nm is typical for clamping the cassette. (About 35 lbs on a 10" long spanner).
Before going that high on torque, I would try the Loctite Blue route first.
If it doesn't work you can always try a higher torque (+Loctite Blue) later.
Click to expand...
This was directed to us by Bosch, during the crank bolt recall.
 
toerag69 said:
hi,

My left crank keeps coming loose. I tighten with 8mm Allen key and crank feels fine but after a few miles it goes loose.

Unsure if my spline, crank arms are OK or not in pictures.

Also does anyone now if there is a correct torque spec for crank arm bolts, just incase I'm not using correct amount torque.

Bike is cube stereo 160 bosch motor.

Thanks

View attachment 185117View attachment 185118View attachment 185119
Click to expand...
I could be wrong, but I don’t see a crank bolt and washer in the pic you provided. Only a crank arm and dust cover.

The main crank bolt, with a washer, is torqued to 50nm (I know that seems high), and the dust cover is only 10-20nm. (Depending on the material used)

That’s been my experience with Bosch CX motors.
 
The problem is the cheap-ass aluminum crank bolts. If you ever drive a set of cranks off your bike that has ISIS cranks just be prepare to secure new crank bolts when you put them back on. One look at the threads of the cheap aluminum crank bolt and you’ll see that are now razor thin. The motor spline is made of hardened steel so no need to worry about that.
 
I’ve just changed the cranks on a Bosch SX system and the recommended torque is 52Nm. It sounds “a lot”, but when you use a torque wrench is quite manageable, but also feels “a lot”. Shouldn’t need any sort of thread lock if it’s torqued up correctly.
 
The issue is almost always the crank interface as crank is alloy, the motor spindle is rarely an issue as its steel

Adding loctite to the bolt is a good idea on a new crank but wont help on the old one if crank is damaged
 
steve_sordy said:
I am not saying that @Funkeydunk is wrong, but 50-60Nm is a seriously high amount of torque for an mtb! For reference 40Nm is typical for clamping the cassette. (About 35 lbs on a 10" long spanner).
Before going that high on torque, I would try the Loctite Blue route first.
If it doesn't work you can always try a higher torque (+Loctite Blue) later.
Click to expand...
SRAM’s XO Bosch cranks say torque to 54nm right on them.
 
Last edited:
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jbrown15 said:
SRAM’s XO Bosch cranks say torque to 54nm right now them.
Click to expand...
Need to make sure to tighten once then back bolt off to relieve tension on the spindle interface and retorque

Will almost always get 1/8-1/4 turn more on the bolt
 
50nm feels toppy to me but knowing the motors, there's no way the spline can't take it. I can't remember the torque value for the chainring nut but they're soft alloy & strip easily whereas the crank spline is steel & threaded internally I.e. the crank itself is a torx shaped affair & the bolt threads on the inside.

Personally, I am a lazy bastard & have never torqued or used Loctite & even though my grease fetish sees mine removed way more than average, it's never worked loose yet, so I guess there is some luck of the draw with them or possibly the tolerances found in different cranks.
 
RustyMTB said:
50nm feels toppy to me but knowing the motors, there's no way the spline can't take it. I can't remember the torque value for the chainring nut but they're soft alloy & strip easily whereas the crank spline is steel & threaded internally I.e. the crank itself is a torx shaped affair & the bolt threads on the inside.

Personally, I am a lazy bastard & have never torqued or used Loctite & even though my grease fetish sees mine removed way more than average, it's never worked loose yet, so I guess there is some luck of the draw with them or possibly the tolerances found in different cranks.
Click to expand...
Torque marked on the chainring nut is 35Nm so that's what I use.
 
Without reading all the replies on this thread.
My way of refitting crank arms is. A little bit of grease on the splines, fit arm and tighten up with a large Allen key. Then get a block of wood on the arm and give it a good smack with a hammer. It's the Neanderthal way of using an impact wrench 🤔
Then tighten up as tight as you dare go with the big Allen key.
They don't come loose, but do come off without any drama with the extractor tool.
That's my mechanics way of tightening up a biggish bolt that causes trouble 👍
I'm going to pull a chair up and wait for all the replies telling me I should use a torque wrench from people who have never used a 6foot one 😁
 
I would totally buy a 6ft torque wrench if I could think of a use for it other than battering anyone who hits my bike with a block of wood.
 
Bear-uk said:
Without reading all the replies on this thread.
My way of refitting crank arms is. A little bit of grease on the splines, fit arm and tighten up with a large Allen key. Then get a block of wood on the arm and give it a good smack with a hammer. It's the Neanderthal way of using an impact wrench 🤔
Then tighten up as tight as you dare go with the big Allen key.
They don't come loose, but do come off without any drama with the extractor tool.
That's my mechanics way of tightening up a biggish bolt that causes trouble 👍
I'm going to pull a chair up and wait for all the replies telling me I should use a torque wrench from people who have never used a 6foot one 😁
Click to expand...
A 6foot torque wrench? I’m definitely not worthy. 😉

The new specs for torque are stamped on the spider/castle nut. 35nm.

The crank bolt torque on a gen5 Bosch (I’ve only done 2 so far) was 50nm.

@Bear-uk, what species of wood do you use …and are you a monster?😉
 
Stihldog said:
A 6foot torque wrench? I’m definitely not worthy. 😉

The new specs for torque are stamped on the spider/castle nut. 35nm.

The crank bolt torque on a gen5 Bosch (I’ve only done 2 so far) was 50nm.

@Bear-uk, what species of wood do you use …and are you a monster?😉
Click to expand...
Only a bit of two x two 🤣
Also apologies for being an arse, but I was in a bad mood as I'd just got back from being dragged out to the supermarket ☹️
I'm sure that says it all 🤔
 
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