nut size

[billyboya]

If you can tighten it 'very tight' there is nothing wrong with the threads. The problem is usually that the taper on the (usually) aluminium crank arm gets distorted when there is any movement. This means the tapers aren't the same so won't lock.

I dont really know what you mean by tapers can you do a picture, also is it possible then to buy seperate pedal arms

 

[sjpt]

also is it possible then to buy seperate pedal arms

By pedal arms do you mean cranks arms? The chunk between the bottom bracket axle and the pedals?

Yes. On cheaper ones the right hand one will have the front chainwheel(s) rivetted on.
On more expensive ones the right hand one will have a spider for fitting the front chainwheels.

You'd probably buy a crankset consisting of two arms and the right hand chainwheel. A very basic set is under a tenner, or you can pay hundreds of pounds.

 

[billyboya]

By pedal arms do you mean cranks arms? The chunk between the bottom bracket axle and the pedals?

Yes. On cheaper ones the right hand one will have the front chainwheel(s) rivetted on.
On more expensive ones the right hand one will have a spider for fitting the front chainwheels.

You'd probably buy a crankset consisting of two arms and the right hand chainwheel. A very basic set is under a tenner, or you can pay hundreds of pounds.

Well at present I only need the left pedal crank arm, as it seems to keep loosening as I pedal, even though the nut is all way in to BB spindle. I thought i had tightened it ok but obviously its not enough. I had thought about putting some thread lock glue on nut, but will i ever be able to undo nut in future if i need to remove BB

 

[sjpt]

Yes, you can buy a left crank arm separately too.
If the crank arm is the correct fit for the BB axle, and you haven't stripped the thread to take the crake remover thread, it's unlikely to be much wrong with the arm.

You may need a washer under the bolt maybe the bolt's too long and hitting the end before it's fully tightened the crank arm.

 

[thelarkbox]

Perhaps the machine screw/bolt used is too long and bottoming out in the spindle/axle before clamping tight, or perhaps some rubbish is blocking the hole or thread?

 

[billyboya]

Yes, you can buy a left crank arm separately too.
If the crank arm is the correct fit for the BB axle, and you haven't stripped the thread to take the crake remover thread, it's unlikely to be much wrong with the arm.

You may need a washer under the bolt maybe the bolt's too long and hitting the end before it's fully tightened the crank arm.

Well Iwill try a washer but the end of bolt seems to be flush with end of crank arm opening

 

[guerney]

After installing my BBS01B, one of the crank arms worked a bit loose so I tightened it tighter the second time, hasn't loosened since. It's easier to apply more force by hand, if the Allen key isn't short. The set I had was short and crap, used these instead. Nice and springy, they don't acquire a permanent bend like the first set.

https://www.amazon.co.uk/gp/product/B079V335CR/

 

[soundwave]

 

[saneagle]

Well Iwill try a washer but the end of bolt seems to be flush with end of crank arm opening

You don't need and shouldn't use a washer.

When you ride a bike with a loose crank, the tapered square becomes no longer straight. Aluminium has a property called "work hardening", which means than when you sqquash it, it goes hard. That makes it more difficult to take the shape of the square taper on the spindle. In that case, you have to heat it up to red hot so that it goes soft again, and it will take the correct shape and go hard again when you tighten the bolt. You only need to do that if it keeps coming loose, so nothing to panic about yet.

In the first instance you should just tighten the bolt very tight and see how you get on. Don't try to solve problems until they actually happen. The most important thing is that there must be no grease or oil on the spindle or else it will come loose again. It needs friction to stay tight. You should clean with petrol or spirit before assembling.

 

[billyboya]

After installing my BBS01B, one of the crank arms worked a bit loose so I tightened it tighter the second time, hasn't loosened since. It's easier to apply more force by hand, if the Allen key isn't short. The set I had was short and crap, used these instead. Nice and springy, they don't acquire a permanent bend like the first set.

https://www.amazon.co.uk/gp/product/B079V335CR/

Yes those allen keys are same as I have, maybe i could add a pipe bit to end of the allen key , to give it more leverage. I will try that today.

View attachment 60418

Yeah that defo will tighten the nut PMSL

You don't need and shouldn't use a washer.

When you ride a bike with a loose crank, the tapered square becomes no longer straight. Aluminium has a property called "work hardening", which means than when you sqquash it, it goes hard. That makes it more difficult to take the shape of the square taper on the spindle. In that case, you have to heat it up to red hot so that it goes soft again, and it will take the correct shape and go hard again when you tighten the bolt. You only need to do that if it keeps coming loose, so nothing to panic about yet.

In the first instance you should just tighten the bolt very tight and see how you get on. Don't try to solve problems until they actually happen. The most important thing is that there must be no grease or oil on the spindle or else it will come loose again. It needs friction to stay tight. You should clean with petrol or spirit before assembling.

Ok I wont use a washer, and like i said above will try tightening the bolt more with the allen key plus a pipe in end of key. But i was a bit worried if it was too tight, but it needs to be alot more than it is now.

would thread lock glue help the bolt to not unscrew or is that not a good idea

thanks all for your suggestions

 

[guerney]

Yes those allen keys are same as I have, maybe i could add a pipe bit to end of the allen key , to give it more leverage. I will try that today.

A pipe might overdo things quite easily I use my cold bare hands and bulging veiny muscles...

would thread lock glue help the bolt to not unscrew or is that not a good idea

That stuff is supposed to be really difficult to remove, especially red threadlock - can be a blow torch job to red hot, apparently. Or so someone mentioned on the forum, I can't remember who.

 

[billyboya]

A pipe might overdo things quite easily I use my cold bare hands and bulging veiny muscles...




That stuff is supposed to be really difficult to remove, especially red threadlock - can be a blow torch job to red hot, apparently. Or so someone mentioned on the forum, I can't remember who.

Ok best to eat tons of spinach then lol, and dont use a pipe on end of key


Ok wont use thread lock glue.

 

[chris_n]

Don't use threadlock, if the arm is coming loose it either is damaged or not tight enough (or both). The torque I mentioned before is approx 30ft lbs so is the equivalent of hanging 30 pounds (weight) on a key that is a foot long. If it helps you visualise what you are doing then us a pipe that is one foot long and turn it with the amount of force required to lift a 30lb weight.

 

[Waspy]

Don't use threadlock, if the arm is coming loose it either is damaged or not tight enough (or both). The torque I mentioned before is approx 30ft lbs so is the equivalent of hanging 30 pounds (weight) on a key that is a foot long. If it helps you visualise what you are doing then us a pipe that is one foot long and turn it with the amount of force required to lift a 30lb weight.

Well, I'm no expert but how come so many of these bolts come with threadlock pre-applied?

 

[guerney]

Bafang bolts had dried on threadlock pre-applied - useless. Wet threadlock can be a different beast entirely, especially the red.

 

[Waspy]

Bafang bolts had dried on threadlock pre-applied - useless. Wet threadlock can be a different beast entirely, especially the red.

I believe there are many different strengths of threadlock, I understand some people use blue Loctite 243

 

[guerney]

Bit tricky when it comes to removal from inside the axle thread, acetone dissolves paint too:

 

[billyboya]

There is no thread lock glue on my bolts. But I am now working on the bike, But I think my problem is, I need to buy a smaller PA disc, as the sensor cannot be placed anywhere else I have tried. I just measured the space on BB spindle for crank arm to fit onto. I marked a line when PA disc is on spindle with a caliper and it said 12.47mm yet the end of pedal arm to fit on BB spindle measures 22.59mm

so I will see if i can find a much smaller PA disc which dont need a seperate sensor attached to bike

 

[guerney]

There is no thread lock glue on my bolts. But I am now working on the bike, But I think my problem is, I need to buy a smaller PA disc, as the sensor cannot be placed anywhere else I have tried. I just measured the space on BB spindle for crank arm to fit onto. I marked a line when PA disc is on spindle with a caliper and it said 12.47mm yet the end of pedal arm to fit on BB spindle measures 22.59mm

so I will see if i can find a much smaller PA disc which dont need a seperate sensor attached to bike

This is why I thought your eventual goal might have been replacement of the BB:

https://www.pedelecs.co.uk/forum/threads/pedal-help.47902/

... but I wasn't sure... then the problem you were trying to solve turned out to be something else on this thread.

 

[chris_n]

Well, I'm no expert but how come so many of these bolts come with threadlock pre-applied?

That type of patch lock doesn't actually harden so is relatively easy to undo unlike a lot of the liquid threadlocks which can be impossible to release.