I need your opinion!

CRANK ARM PROBLEMS!

I have a problem chaps, my** left crank arm (165) **has come loose and I want to know if it is necessary to buy another one to replace it.
Is it worth cashing out on a good quality crankset or just replacing the arm?
Please note that this is the second time this has happened to my bike.

Links to the pictures are below:

• Picture of how worn out the material is
  
• Picture of the left crank arm
  
• Picture of the bottom bracket (left drive side)
  
  

Thanks! :)

*PROWHEEL FORGED 2N 165 - That's the name/make of my crank arm

Looks like you've been riding with it loose for a while. You shouldn't round-off the taper like that if it was tight when you were riding it.

Can't really see how worn the bottom bracket spindle is from that photo. If it isn't too badly worn you could try putting the crank arm back on and making sure it's properly tight and ride it to see if it comes loose again. i.e. tap the crank arm on with a rubber mallet so it sits on without wobbling, then tighten it with a socket set and LONG extension to get it well tight

Does the crank arm go onto the bottom bracket spindle all the way now? All the way until the flats on the spindle finish, or have you still got some room to play with?

If you can afford it replace both the crank and the bb. If you cant, go buy some thread lock and tighten the bolt up good and proper with plenty of thread lock.

Ah!
Just checked the bolt/screw, and it appears that the threading is coming off. Hmm.
I will try what you said to do Stu F and I will post back with results!

Thanks :)

difficult to see the real extent of wear on the square taper on a photo. Do you think there's a chance you didn't tighten the crank bolt enough so that it came loose? Park-Tools recommend 305-391 lbs/in torque. If you think this may be the case, try it again, the worst that can happen (appart from falling off 100miles from home) is splitting the casting in which case you'll have to replace it. I replaced a L/H crank arm on my road bike with a non-branded one and noone has ever noticed it! Also, it cost me under £10 so I was happy.

NB. if you don't have/can't borrow a torque wrench, it might be worth taking it to your LBS

I will post back later after I have a little ride around the block (after Stu F's method).
*and take a more clearer picture(s) of my bb! ;)

dude, if something like that happens second time [assuming the BB is the same]
are they both JIS?
happened to me once, when someone sold me a BB saying it was JIS when it wasnt. you know the difference between ISO and JIS, right?
http://sheldonbrown.com/bbtaper.html

The crank is made of soft alloy and the bottom bracket spindle is hard steel. When the bolt comes loose the crank rocks on the taper and by the time it has come loose it is distorted. The axle meantime is undamaged.
Get a new l/h crank and a new bolt and tighten the bolt properly. And check that the bolt is still tight from time to time. The bolt will inevitably work loose after a while.

RESULTS:

**[Before ride] **Applied Stu F's method, by hammering my crank arm into the bb as far as I could, then tightening the bolt/screw. This proved my crank arm to be as it should be during normal (casual riding).

[After ride] Crank arm has come loose, and was wobbling after a good 30 seconds of riding (I noticed). For some reason, the screw/bolt is in tact but could be obvious that the threading is f**ked.

*Note that my left crank arm is the one I push down on when I want to skid. (I am riding Fixed).

^^ I assumed he meant with the same crank. You will never get the old crank to work once it has come loose.

I'm sorry, I haven't a clue as to which BB I have.
This is my first proper bike from my old bmx (which was for children)!

well thats my guess anyway. do some reading and find out what you got, certainly wont hurt even if thats not the case.

http://www.youtube.com/watch?v=6h9JTz0kOD0

you need new cranks

as you don't know what king of BB you have, it's most likely going to be JIS taper. Most cheap cranks use JIS taper.

^^ this

Get a new crankset. Get a new BB. Make sure you check the crank bolts and tighten them regularly. Especially when they are new. And tighten the chainring bolts at the same time. They like to come loose too.

If you do them up properly the first time you shouldn't need to retighten any of them.

Bolts stretch.

Chains get dirty.

shims get inverted