Crank arm thin walled socket to access

[Hornby]

Hi, is there a tool available to remove the nut which holds the crank arm on? I want some sort of socket which is thin walled to get onto the nut and be able to be tightened with a torque wrench. Thanks, Paul J

 

[Ajax Bay]

Assuming you are talking about crank bolts holding a crank onto a square taper spindle, I (unhelpfully) find that a normal 14mm socket (from a normal socket set) fits a bolt which has a hexagonal head. The diameter of the space to get the socket in is >18mm.
If the spindle is of the type (likely 30+ years old) that has a protruding threaded boss then the nut will normally be a 14mm nut (and unscrewed the same way).
Sheldon worth a quick scan: https://sheldonbrown.com/tooltips/cotterless.html https://sheldonbrown.com/bbtaper.html
Most crank bolts 'nowadays' are undone with a ?6mm allen key.
Why do you feel the need to use a torque wrench? The spindle is steel; the cranks are robust Al alloy. The bolt just needs to be 'tight' (so tighten it, hit the crank with a rubber mallet and tighten it again: job done.
In use, because the interface has that taper, the crank will squirm up the taper till it can't. You should not regularly tighten the bolt: zero need. If you do there's a risk of damaging the crank.

 

[Hornby]

Assuming you are talking about crank bolts holding a crank onto a square taper spindle, I (unhelpfully) find that a normal 14mm socket (from a normal socket set) fits a bolt which has a hexagonal head. The diameter of the space to get the socket in is >18mm.
If the spindle is of the type (likely 30+ years old) that has a protruding threaded boss then the nut will normally be a 14mm nut (and unscrewed the same way).
Sheldon worth a quick scan: https://sheldonbrown.com/tooltips/cotterless.html https://sheldonbrown.com/bbtaper.html
Most crank bolts 'nowadays' are undone with a ?6mm allen key.
Why do you feel the need to use a torque wrench? The spindle is steel; the cranks are robust Al alloy. The bolt just needs to be 'tight' (so tighten it, hit the crank with a rubber mallet and tighten it again: job done.
In use, because the interface has that taper, the crank will squirm up the taper till it can't. You should not regularly tighten the bolt: zero need. If you do there's a risk of damaging the crank.

Thanks Ajax, I think the bike will be over 30 years old or near. I have just changed the cranks due to them continually coming loose on the spindle. I had to use a box spanner on the old cranks because my socket wouldn't fit in the crank hole to loosen the nuts. I will try with the new cranks on. I was wanting to torque the nuts just to make sure that they were tight enough and so not damage the new cranks if they weren't. Do you know what the torque setting is for this type of bike spindle? I have seen varied psi settings for different bikes

 

[andrew_s]

A shimano crank puller has a 14 mm socket in the end that's intended to fit and remove the crank bolts (if they are 14 mm hex rather than allen key). As you and Ajax Bay have between you demonstrated, the 14 mm socket from a socket set may or may not fit down the hole.

As @Ajax Bay notes, a torque wrench isn't usually used - it goes on as tight as you can reasonably get it by hand with a 10" adjustable, and should then be left alone.

 

[Low Gear Guy]

Standard socket heads are too wide to fit inside the crank. You will need the thin-walled version that comes with the crank puller.

 

[Mike Ayling]

A shimano crank puller has a 14 mm socket in the end that's intended to fit and remove the crank bolts (if they are 14 mm hex rather than allen key). As you and Ajax Bay have between you demonstrated, the 14 mm socket from a socket set may or may not fit down the hole.

As @Ajax Bay notes, a torque wrench isn't usually used - it goes on as tight as you can reasonably get it by hand with a 10" adjustable, and should then be left alone.

Just nip it up and and check once a month or so.

 

[rogerzilla]

Tighten to the recommended torque with a greased bolt. Ride for 100 miles. Re-torque, remove bolts, clean all threads and refit with threadlock. Don't touch again until the BB wears out.

 

[Yellow Saddle]

Just nip it up and and check once a month or so.

No, this is a recipe for failure. Although "nip it up" is subjective and can be read in many ways, a typical "nip" is not good enough. A square taper crank has to be torqued to 40NM for good reason. At 40NM it will not come loose by itself and instead, tighten itself by creeping even further up the crank to a point where the nut is superflous and often just falls out if there isn't a captive cap on the crank.

An analogy to try and understand the mechanism behind the phenomena is to imagine the four sides of the square taper on the crank to be lined with stiff brush bristles. If you now force the crank onto a male square taper, you'll see that the bristles bend backwards as the crank is pushed in. If you now pedal, one of the square faces, at each quadrant of rotation gets a bit of relief from the friction holding the bristles back, deforms and the bristles just pack to horizontal. In the process, the crank creeps up the taper. This is of course only possible if the bolt prevents it from going backwards.

This analogy is similar to what happens in the crank in real life. The square hole squirms when pedalling, relieving axial friction and the crank creeps.

Therefore, torque it once, properly, go ride and leave it alone. It will not come off.

Note that this mechanism is only relevant to square taper, not Octalink and ISIS drive.