What does a crank arm fixing bolt do?

Crank bolts, as the name suggests, are used to secure the crank to the axle (spindle) of the bottom bracket(BB). Signs of this may include a tell-tale creaking noise from the BB area, or ‘play’ in the crank arms when moved from side to side by hand.

Why does my left crank arm keep coming loose?

If you’ve been repeatedly riding with a loose crank arm it could be that it’s now damaged. You could try tightening with lots of torque, grease on the square taper and threadlocker (e.g. blue Loctite, but in a pinch any kind of glue works) on the threads.

Why does my crank arm keep falling off?

What’s most likely happening when a bolt will not keep a crank arm tight on the spindle, despite being tightened to torque, is that the crank arm interface is damaged in some way. The splines on the crank arm can be ovalized or otherwise damaged if ridden when loose.

Can you over tighten crank arm?

Yes, it is possible The bigger problem with over tightening a square taper is that crank arm can be deformed to the point where it will not stay tight. I always use a torque wrench when tigtening crank bolts to avoid over tightening.

What size is an M8 bolt?

Dimensions for DIN931 Hex Head Bolt

Diameter (d) Pitch Across Flats (s)
M5 0.8mm 8mm
M6 1.0mm 10mm
M7 1.0mm 11mm
M8 1.25mm 13mm

Are crank bolts universal?

The female-threaded “outer” part has a standard external diameter of 10mm, so any crank bolt will fit into any chainset. That does not, however, mean that any set of crank bolts will work for every chainset.

Why does my pedal keeps falling off?

If a pedal is loosening itself, it’s not because of screw loosening forces, it’s because the crank threads are bad, and threadlock will not help. However, if the threads are still good then threadlock can cause the pedal to bind terribly such that the pedal won’t ever come off.

How tight should crank arm bolts be?

Registered. Most square taper crank arms should be 29 ft-lbs. That is pretty darn tight. As has been mentioned, if it came loose, the crank arm is likely damaged beyond repair already and needs to be replaced.

How do you keep a bolt from loose?

The best way to prevent nuts and bolts from working loose, due to vibrations, is to use a locking device. Some examples of locking devices include flat washers, spring washers, and mechanical screw locking flange nuts.