Alternate Crank set and pedals

[larry-new]

Agree totally.
My note was in response to his original note, wondering if he needed to keep an extra pair on hand.

Ahhh...no. That this even happened once is weird, doncha think?

 

[larry-new]

Well, we're certainly pedalling this one to the finish, myself more than anyone.

Just did some follow-up research, and one of my long held assumptions has been punctured....woosh! Pedals do not self tighten, they self loosen. The original setup with the different threads was so if the pedal bearings siezed on a fixed gear, as in the original years of the Tour de France, the rider would not break their ankles. Go figure.

So, back to the OP. What you experienced is rare. Get a new crank and pedals, grease the threads, and tighten to spec. You should be fine. Also grease the square bottom bracket, and go back to tighten those two bolts several times, as they will set in, as they tighten on a taper.

 

[AHicks]

Ahhh...no. That this even happened once is weird, doncha think?

My point exactly Larry. Therefor no need to keep an extra set of anything in stock.

 

[rich c]

My point exactly Larry. Therefor no need to keep an extra set of anything in stock.

Crank threads stripping out is a very common post on the Sondors owners Facebook page. Over 8,000 members showing the results of heavy fat tire EBikes, with cheap alloy cranks, and DIY assembly and poor maintenance.

 

[AHicks]

Thanks Rich. I had no idea that could be that big a deal, even at the hands of raw first timers/amateurs.

 

[Alaskan]

I have first hand experience destroying the threads in an alloy crank because I installed new pedals and over tightened them. One of the dangers of being your own bike mechanic is proceeding without asking around first.

In speaking with a professional cyclist/friend, he recommended greasing the threads and tightening the pedals just slightly beyond hand tight, no more than 1/8 turn. My experience has proven that the pedals are tightened further during your first ride, especially if you climb a decent hill. You will need at least an eight inch long wrench to get the pedals off the next day as the leverage of your feet on the pedals tightens the pedals enough.

Given the thread pattern, your pedaling with naturally tighten the pedals just right. The only way they will ever come loose is if you damage the threads in the alloy of the crank by overtightening the pedals.

 

[AHicks]

I would have agreed that the threads have a natural tightening action to them until a few minutes ago. I was mulling this over after Larry's note above, and thinking he's on to something. If the pedal bearing were to seize up, our natural pedaling motion is going to UNscrew that pedal, no?

 

[Alaskan]

I would have agreed that the threads have a natural tightening action to them until a few minutes ago. I was mulling this over after Larry's note above, and thinking he's on to something. If the pedal bearing were to seize up, our natural pedaling motion is going to UNscrew that pedal, no?

Not true, The natural pedaling rotation will still only want to tighten the pedals on to the crank arms. If the pedal bearings seize you just will not be able to rotate the cranks with the pedals but you will still be trying to tighten them. You will only be able to theoretically unscrew the pedal if you pedal backwards and the free wheel is seized.

 

[larry-new]

Not true, The natural pedaling rotation will still only want to tighten the pedals on to the crank arms. If the pedal bearings seize you just will not be able to rotate the cranks with the pedals but you will still be trying to tighten them. You will only be able to theoretically unscrew the pedal if you pedal backwards and the free wheel is seized.

So said I, until I was asked to visualize it, then the walls fell.

Here proof in a more concrete form: Put your bike on its stand. Loosen either pedal with a wrench, and keep the wrench on the pedal.
Now rotate the crank in reverse, pedalling backwards, letting the pedal and crank rotate, but not the spindle and your wrench.

Voila! The pedal tightens! (The opposite is so ingrained in my head that I had to stop and actually do this while typing.)

 

[AHicks]

Yup, and if you pedal forward with that wrench still in place, the pedal will soon be on the floor....

That's pretty much exactly opposite of the way it should be to my way of thinking as well...

 

[redhotlava]

One side is right thread, one side is left thread, is that the problem? Pedals are made for a certain side.

No, R on right side, L on left

 

[redhotlava]

What kind of wrench are you using to secure the pedals to the crank arm? Even though pedals are threaded in such a way as to promote them staying on, pedals need to be tightened properly from the get-go. Shimano recommends a minimum of 35 Nm of torque. If you use a small wrench, like a 6" adjustable "Crescent" wrench, you need to tighten down hard to get to that amount of torque.

I actually purchased a pedal wrench and a torque wrench for the crankset and pedal install. I don't know, it's possible it came loose on the very last ride, but I constantly checked it, it wasn't loose from what I could tell, but hey, maybe just tight enough after riding and slowly loosening to point it came off pretty quick. On that trail there are a lot of winds, up and down and I lean into it on the turns and when pedaling.

 

[redhotlava]

Just wanted to say thanks for the feed back and the questions, appreciated gents. I'll keep you posted as to my next move, should these be replaced under warranty or if I have to make a purchase. I'll be sure not to over-tighten the pedals and give them more attention checking them after the install again.

 

[Alex M]

Here proof in a more concrete form: Put your bike on its stand. Loosen either pedal with a wrench, and keep the wrench on the pedal.
Now rotate the crank in reverse, pedalling backwards, letting the pedal and crank rotate, but not the spindle and your wrench.

Voila! The pedal tightens!

It tightens because you've simulated the scenario of the failed bearing.
When bearing works, pedaling backwards loosens pedals and pedaling forward - tightens.

 

[Alaskan]

@larry-new you are right. I get it. However in order to actually loosen the pedal spindle off of the crank arm it would have to be broken free in order to keep the pedal in a constant flat attitude. I think as a practical matter, something has to give, either the bearing or the spindle thread connection to the crank. The more likely scenario if the pedal bearing is seized, you would just stop cranking.

 

[larry-new]

It tightens because you've simulated the scenario of the failed bearing.
When bearing works, pedaling backwards loosens pedals and pedaling forward - tightens.

It can't tighten if the bearing is working. It can't tighten because it's the wrong direction.

 

[Alex M]

It can't tighten if the bearing is working. It can't tighten because it's the wrong direction.

If everything works, it will tighten when you pedal forward.
Ex, clockwise rotation of the right crank transfers the effort to the spindle in the same clockwise direction - i.e. tightening.

You may repeat the same experiment as above, only without holding the spindle immobile relatively to the pedal, and watch the relative movement of the parts.

BUT, if pedal bearings seize, pedal loosens when pedaling forward. (I agree with Alaskan that you most likely would stop pedaling in this case). Gotta love this throttle

Edit-PS: when spindle is not sitting properly, i.e. already loose or cross-threaded, then in addition to "pure rotation" you're getting lateral movements and lateral forces trying to break the pedal off, and then anything can happen. Don't know how likely it is to loosen then, more likely it will destroy the threads and seize even more - or just break.

 

[MadManMark]

...much softer so it is also a good idea to put a little grease on the threads before threading them in.

This was the most head-scratching thing* for me about the pair of bikes I bought a couple months ago: why didn't they include a small tube of grease? I mean, they literally supply you with everything else you need to assemble the bike -- right down to the tools! I even sent a message to Radpwoer suggesting it.

* with the possible exception that I don't understand why the clamps to attach the fenders to the fork are soft plastic instead of rubber-coated metal; two of mine cracked before I realized the problem I had with not getting them tight enough was that they needed shims on the inside because they were slightly oversized, not tightening them more. I didn't take much force with the wrench to crack them.

 

[Alex M]

Mark - I guess they forgot that they ship the bike only partially assembled ... Grease is cheap, no big deal. With the long journey in cargo ship from China the boxes get smashed (yes, they do). Grease would leak and make a mess.
Plastic clamps I don't understand, they could've made it of cheap metal, it would last forever.

 

[larry-new]

If everything works, it will tighten when you pedal forward.
Ex, clockwise rotation of the right crank transfers the effort to the spindle in the same clockwise direction - i.e. tightening.

You may repeat the same experiment as above, only without holding the spindle immobile relatively to the pedal, and watch the relative movement of the parts.

BUT, if pedal bearings seize, pedal loosens when pedaling forward. (I agree with Alaskan that you most likely would stop pedaling in this case). Gotta love this throttle

Edit-PS: when spindle is not sitting properly, i.e. already loose or cross-threaded, then in addition to "pure rotation" you're getting lateral movements and lateral forces trying to break the pedal off, and then anything can happen. Don't know how likely it is to loosen then, more likely it will destroy the threads and seize even more - or just break.

Ok, take a loose pedal, hold it against the crank arm, and simulate pedalling forward...let me know when it tightens. I will not hold my breath awaiting your sucess.