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Proper way to torque a crank bolt on a square taper spindle?
#1
I've watched the Park Tool video on removing and installing a new crank. I've completed the removal/install and torqued to 45Nm (hoping this is correct for a cheap SR Suntour XCT since I can't find manufacturer guidance). I used a tiny bit of grease (but let's not go down that rabbit hole for this question).

Here's where I'm starting to find conflicting info.

This document on Sheldon's siteexplains that re-torquing the retaining bolt can lead to the crank splitting.

However, I've seen advice lots of times suggesting to re-torque after the first ride or the first few rides. Is this really advisable?

I've seen other advice that suggests to keep checking the torque as an ongoing maintenance thing (which really can only mean re-torquing it). So this seems to be what the document on Sheldon's site is saying not to do.

Where/when do you draw a line? What do bike shops do when installing cranks as they're probably not re-torquing it after the first few rides for someone? Or how are new bikes assembled and sold to customers who probably don't have any problems ever?

Note: cross posted from a reddit post based on a recommendation from someone from this community.
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#2
hi Whitney. I personally do not treat it (crankset torque) as an ongoing maintenance. install the crank, do not forget to follow the torque specifications, do a one-time checkup after 2-4 rides. if necessary, do a bit of re-torquing.
  Reply
#3
What Papa Dom said!
Take care,
Jesper

"I am become Death, the destroyer of bicycles." NJS
  Reply
#4
(09-20-2020, 07:07 AM)Papa Dom Wrote:  hi Whitney. I personally do not treat it (crankset torque) as an ongoing maintenance. install the crank, do not forget to follow the torque specifications, do a one-time checkup after 2-4 rides. if necessary, do a bit of re-torquing.

Thanks!
  Reply
#5
(09-20-2020, 02:13 PM)Jesper Wrote:  
(09-18-2020, 11:36 PM)Whitney Young Wrote:  I've watched the Park Tool video on removing and installing a new crank. I've completed the removal/install and torqued to 45Nm (hoping this is correct for a cheap SR Suntour XCT since I can't find manufacturer guidance). I used a tiny bit of grease (but let's not go down that rabbit hole for this question).

Here's where I'm starting to find conflicting info.

This document on Sheldon's siteexplains that re-torquing the retaining bolt can lead to the crank splitting.

However, I've seen advice lots of times suggesting to re-torque after the first ride or the first few rides. Is this really advisable?

I've seen other advice that suggests to keep checking the torque as an ongoing maintenance thing (which really can only mean re-torquing it). So this seems to be what the document on Sheldon's site is saying not to do.

Where/when do you draw a line? What do bike shops do when installing cranks as they're probably not re-torquing it after the first few rides for someone? Or how are new bikes assembled and sold to customers who probably don't have any problems ever?

Note: cross posted from a reddit post based on a recommendation from someone from this community.

Welcome Whitney,

I have to consider this quite often since I am rebuilding bikes that are 30 years old or more using originally installed and used period replacement parts. All are square taper cranks, but not all are identical or 100% interchangeable. Most older taper cranks have been removed more often than newer ones because of BB maintenance/adjustment and mating surfaces can become worn/damaged due to servicing. I'm not overly familiar with the splined cranks. Taper cranks if worn internally, or if using JIS or ISO cranks and BB spindles interchanged may cause problems if the crank gets "bottomed out" on the area where the taper meets the main shaft when tightening, or if the crank can't be tightened if the bolt contacts the end of the spindle. I have never used a torque wrench on the taper style crank bolts because I tend to use the same style (ISO) and often manufacturer for cranks and BBs. I also regularly check these and other mounts/connections on the bike after initial service/test ride, and before any serious riding. I have never had to "retighten" a crank arm, nor have I had one crack during installation or during use. Probably somewhat lucky since I rarely know the history of the part, but with new cranks properly fitting the spindle you should not be having issues with loose and/or damaged cranks after proper installation. If re-torquing to the same spec after initial torquing and use, then you should not be able to tighten any more excluding an almost imperceptible amount due to bolt "stretch"; but even then you should still be within the minimum torque tolerance and you do not need to re-torque unless it was done improperly in the first place. You should certainly not be cracking properly fitted cranks just because you are torquing them to specification, whether the first time or the twentieth. That's what the specs are there for in the first place, to avoid damaging the part during installation and when under engineered maximum use loads. Thus, in my opinion there is nothing wrong with re-torquing any part on any equipment within specs. Always follow manufacturers specs when provided; my old stuff rarely has any specs.

Thanks!
  Reply
#6
(09-18-2020, 11:36 PM)Whitney Young Wrote:  I've watched the Park Tool video on removing and installing a new crank. I've completed the removal/install and torqued to 45Nm (hoping this is correct for a cheap SR Suntour XCT since I can't find manufacturer guidance). I used a tiny bit of grease (but let's not go down that rabbit hole for this question).

Here's where I'm starting to find conflicting info.

This document on Sheldon's siteexplains that re-torquing the retaining bolt can lead to the crank splitting.

However, I've seen advice lots of times suggesting to re-torque after the first ride or the first few rides. Is this really advisable?

I've seen other advice that suggests to keep checking the torque as an ongoing maintenance thing (which really can only mean re-torquing it). So this seems to be what the document on Sheldon's site is saying not to do.

Where/when do you draw a line? What do bike shops do when installing cranks as they're probably not re-torquing it after the first few rides for someone? Or how are new bikes assembled and sold to customers who probably don't have any problems ever?

Note: cross posted from a reddit post based on a recommendation from someone from this community.

Welcome Whitney,

I have to consider this quite often since I am rebuilding bikes that are 30 years old or more using originally installed and used period replacement parts. All are square taper cranks, but not all are identical or 100% interchangeable. Most older taper cranks have been removed more often than newer ones because of BB maintenance/adjustment. I'm not overly familiar with the splined cranks. Taper cranks if worn internally, or if using JIS or ISO cranks and BB spindles interchanged may cause problems if the crank get "bottomed out" on the shoulder area where the taper meets the main shaft, or if the bolt head contacts the end of the spindle. I have never used a torque wrench on the taper style crank bolts because I tend to use the same style (ISO), and often the same manufacturer for cranks and BBs. I also regularly check (by hand/eye, no tools) these and other mounts/connections on the bike after initial service/test ride, and before any serious riding. I have never had to "retighten" a crank arm after a test ride re-tweaking, nor have I had one crack during installation or during use. Probably somewhat lucky since I rarely know the history of the part, but when using new cranks properly fitting the spindle you should not be having issues with loose and/or damaged cranks after proper installation (barring defects). If re-torquing to the same spec after initial torquing and use, then you should not be able to tighten any more excluding an almost imperceptible amount due to bolt "stretch" and the crank seating under normal load; but even then you should still be within the minimum torque tolerance and you should not need to re-torque unless it was done improperly in the first place. You should certainly not be cracking properly fitted cranks just because you are torquing them to specification, whether the first time or the twentieth. That's what the specs are there for in the first place, to avoid damaging the part during installation and when under engineered maximum use loads. Thus, in my opinion there is nothing wrong with re-torquing any part on any equipment within specs. Always follow manufacturers specs when provided; my old stuff rarely has any specs.

IMPORTANT: CALIBRATE YOUR METERING EQUIPMENT, WRENCHES, GAUGES, ETC.!
Take care,
Jesper

"I am become Death, the destroyer of bicycles." NJS
  Reply


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