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Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 5:53pm
by jamesofyorkshire
Hello.
I thought the Shimao crank arm fixing bolts for Hollowtech 2 would be all the same size but apparently not.
My plastic 'bolt' has just split in half so I need to buy another.
My RH crank(set) is 5800. My LH crank arm is 7900. Do I order the crank arm fixing bolt for the 5800 or the 7900? They are different lengths and I don't know if it's the crankset part that's the one that counts or the crank arm.
Any advice much appreciated.
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 5:57pm
by Jdsk
Is that part 5 in this diagram?
Thanks
Jonathan
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 6:20pm
by jamesofyorkshire
Yes.
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 6:24pm
by mattsccm
Cheap alloy ones from Aliexpress work nicely.
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 6:28pm
by Paulatic
The threads are in the rhs you’d think you need the 5800.
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 6:38pm
by Eyebrox
Paulatic wrote: ↑24 Oct 2022, 6:28pm
The threads are in the rhs you’d think you need the 5800.
Agree. It's screwing into the internal of the 5800 crank arm.
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 7:22pm
by keyboardmonkey
If answering ‘Yes’ to the question “Is that part 5 in this diagram?”, you want a ‘Crank Arm Fixing
Screw’ rather than bolt, which is a different kettle of ball games.
According to this Tech Doc the 5800 part number is Y1P417000:
https://dassets.shimano.com/content/dam ... -3714C.pdf
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 7:51pm
by Paulatic
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 8:37pm
by jamesofyorkshire
Thanks to all respondents.
I know the plastic bolt/screw goes into the 5800 but maybe the 7900 arm is a bit thinner where it attaches?
Hence my question which is the primary constituent to consider. If all the plastic bolts/screw were the same it wouldn't be an issue.....but that would make it too easy wouldn't it.
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 8:55pm
by keyboardmonkey
Ha ha. They don’t make it easy for mere mortals do they?
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 8:57pm
by keyboardmonkey
jamesofyorkshire wrote: ↑24 Oct 2022, 8:37pm
Thanks to all respondents.
I know the plastic bolt/screw goes into the 5800 but maybe the 7900 arm is a bit thinner where it attaches?
Hence my question which is the primary constituent to consider. If all the plastic bolts/screw were the same it wouldn't be an issue.....but that would make it too easy wouldn't it.
Buy one of each and let us know how you get on?
P&P is probably greater than the parts if you buy online. Hope you get sorted anyway.
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 9:29pm
by jamesofyorkshire
Yeah, that's what I plan to do. I was hoping one of the experienced tech wizards on here would know the answer and save me a few quid.
I've just started a 3 week cycling holiday in The Borders and second ride in.....my left crank came loose. Made it back to base where I have all the tools, tried to tighten the plastic bolt/screw to realise it had sheared so wouldn't tighten. I have enough parts to build another bike given another frame, but do I have that cheapo plastic bolt/screw.....obviously not.
Re: Shimano crank arm fixing bolt size?
Posted: 24 Oct 2022, 9:58pm
by keyboardmonkey
jamesofyorkshire wrote: ↑24 Oct 2022, 9:29pm
Yeah, that's what I plan to do. I was hoping one of the experienced tech wizards on here would know the answer and save me a few quid.
I've just started a 3 week cycling holiday in The Borders and second ride in.....my left crank came loose. Made it back to base where I have all the tools, tried to tighten the plastic bolt/screw to realise it had sheared so wouldn't tighten. I have enough parts to build another bike given another frame, but do I have that cheapo plastic bolt/screw.....obviously not.
The part is effectively a preload cap which is fastened finger tight, isn’t it? Then the two bolts are tightened at quite a high torque. In theory the ‘Crank Arm Fixing Screw’ could be removed once the two bolts are snugged down. I wonder if, given the mismatch of parts you mention, there is something else going on.
Re: Shimano crank arm fixing bolt size?
Posted: 25 Oct 2022, 7:13am
by jamesofyorkshire
Mismatch? They are both Hollowtech 2 so fit together, and work together just fine. This post isn't to ask if the components work together as, after 20,000 miles, they obviously do. The post is to ask which length of the plastic 'preload cap' is required, as the original one has just failed, probably due to age.
Re: Shimano crank arm fixing bolt size?
Posted: 25 Oct 2022, 8:30am
by keyboardmonkey
jamesofyorkshire wrote: ↑25 Oct 2022, 7:13am
Mismatch? They are both Hollowtech 2 so fit together, and work together just fine. This post isn't to ask if the components work together as, after 20,000 miles, they obviously do. The post is to ask which length of the plastic 'preload cap' is required, as the original one has just failed, probably due to age.
Well okay then. It’s just that under normal fitting/use the plastic part shouldn’t be under so much pressure that it fails and if properly torqued those two bolts holding the crank arm on shouldn’t be coming loose:
jamesofyorkshire wrote: ↑24 Oct 2022, 9:29pm
… I've just started a 3 week cycling holiday in The Borders and second ride in.....my left crank came loose…
Anyway, as I say I hope you get sorted.
