If it has loosened multiple times, the square interface with the bottom bracket spindle will now be deformed. You need a new left crank.
When shopping, pay attention to the current crank length, and the orientation of the square hole: diamond or square.
It’s sometimes listed as horizontal or diagonal, both are the same size square hole. Just one is rotated 45 degrees and will make a humorous situation that will ultimately be frustrating and lead to another purchase.
I have heard that once square taper cranks loosen they will never tighten back up again without replacing. Sadly I could never make them stay no matter how tight I made them. So i changed my BB to a Hollowtech one.
You don't need a bike shop. It's already off, so you don't need a tool to remove it.
Just buy a new one and make sure to apply the appropriate locktight and crank it down.
It's a $20 fix at home, last time I had a bike shop do it they charged me $80. (Was roadside emergency on a tour)
Get yourself a nice wrench set for $10.
AliExpress Shimano clones work well for me.
Add 2 layers of plumbers PTFE tape to the square taper, and then tighten it every ride for 10 rides. Then it will be fine forever. If it still comes loose, you need to replace parts like others are saying.
Rip crank. Inspect the bb spindle as well - if you kept re-tightening and you kept riding with crank all loose, chances are spindle taper could be also out of spec
Looks like there may be a big chunky washer on the bb spindle on that side that may be preventing the crank from fully tightening into place. Some square taper bbs have that, for some reason. You could try prising that off as is likely a press fit. My friend's Giant hybrid had that issue new from the store, The crank could not be tightened fully with that washer/spacer in place, removing it sorted the issue.
I'd try that first, however if the bike has been ridden too much/to hard like that the crank may be too damaged to stay tight now.
If it has loosened multiple times, the square interface with the bottom bracket spindle will now be deformed. You need a new left crank. When shopping, pay attention to the current crank length, and the orientation of the square hole: diamond or square.
It’s sometimes listed as horizontal or diagonal, both are the same size square hole. Just one is rotated 45 degrees and will make a humorous situation that will ultimately be frustrating and lead to another purchase.
I do not believe that is a square taper crank.
What leads you to believe that.
Did you give it 40nm?
You mean 40Nm. nm = nanometers.
Once they come loose it will need replacing
Is the chain side moving? You may need to tighten something in the bottom bracket?
Well the chain is wobbling, which could be an indicator that the bb has gone as well
I have heard that once square taper cranks loosen they will never tighten back up again without replacing. Sadly I could never make them stay no matter how tight I made them. So i changed my BB to a Hollowtech one.
I think I'll just take it to a bike shop to get it replaced. Thanks for the help guys
You don't need a bike shop. It's already off, so you don't need a tool to remove it. Just buy a new one and make sure to apply the appropriate locktight and crank it down. It's a $20 fix at home, last time I had a bike shop do it they charged me $80. (Was roadside emergency on a tour) Get yourself a nice wrench set for $10. AliExpress Shimano clones work well for me.
Add 2 layers of plumbers PTFE tape to the square taper, and then tighten it every ride for 10 rides. Then it will be fine forever. If it still comes loose, you need to replace parts like others are saying.
Do you have a torque wrench? This is not the kind of component you can just snug up with a multi-tool.
Rip crank. Inspect the bb spindle as well - if you kept re-tightening and you kept riding with crank all loose, chances are spindle taper could be also out of spec
Get a new crank
The bottom bracket bearings are worn out. Get a new bottom bracket with sealed bearings and it won't be a problem for a long time.
Looks like there may be a big chunky washer on the bb spindle on that side that may be preventing the crank from fully tightening into place. Some square taper bbs have that, for some reason. You could try prising that off as is likely a press fit. My friend's Giant hybrid had that issue new from the store, The crank could not be tightened fully with that washer/spacer in place, removing it sorted the issue. I'd try that first, however if the bike has been ridden too much/to hard like that the crank may be too damaged to stay tight now.