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Re: bike pedal arm keeps falling off as i pedal.
You need a new crank arm. If you ride with the nut loosened what happens is the square part of the bottom bracket shaft wears the hole out in the aluminum crank and it no longer fits snugly no matter how much you tighten it down.
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Loosen the nut that holds the back wheel and pull it back until the chain is tight and then retighten the nut. If when the chain is tight, the wheel is not on the rear frame, you need to take a link out of the chain.
Chains usually fall off because the chain is not tight enough. With the bike sitting upside down on the seat and handle bars the nuts on the rear axle should be loosened and the axle moved rearward so the chain tightens. When it is tight the nuts can be tightened. In addition to having a tight chain the rear axle nuts adjust the alignment of the wheel to the frame. You know you have it right if both the chain is tight and the tire closest to the crank is centered in the frame. The nuts should be tight enough so they don't allow the axle to move when you ride it. I hope this helps.
If you have a look underneath the seat, at the back, you'll see a silver nut and bolt. Get the seat up to the height you want, and then tighten this nut and bolt VERY tight, and your problem will be fixed. Easy?
the little balls are the bearings, ie: ball bearings, so they are the size, take them to a bike shop and get a replacement kit. Your crank is probably not bent , it takes a big crash or something to bend one. there is an adusjment nut and lock nut to set them back up. could be LH thread on the left hand side
Your pedal falling off is never a good thing, nor is the entire crank arm assembly.
For this one you are best taking it into your local bike shop and have them take a look at why both of these fell off. There are a number of reasons, from stripped thread to missing bolts and nuts to improper assembly. None of these are a good scenario with a childs bike, or any bike for that matter.
Alternative, and my personal suggestion - Take the bike back to where it was purchased and exchange for a new one. These parts should not fall off after years of riding let alone 2 days, and would constitute a warranty and safety issue.
I WOULD NOT RECOMMEND CONTINUING TO RIDE THIS BIKE, SINCE YOU DO NOT KNOW WHAT ELSE WAS IMPROPERLY ASSEMBLED.
Yes, the crank-arm could be replaced.
1.You would need to remove the flat nut holding the crank to the frame. And then take out the bearing.
2. A special open-ended wrench is required to remove this nut. Please visit your local bicycle shop for a new crank-arm, and the required tools, also.
3. Put in new crank-arm and its bearing.
4. Grease the bearing.
5. Tighten nut.
6. Give it a test ride.
Crank bolts are rarely ckecked when building a bike, they are usually tight from the factory and don't need to be looked at.
Sometimes they are not, but you can fix it at home if you have metric socket tools and a ratchet handle.
Grab a small flat blade screwdriver and pry off the grey plastic cap, you should find the nut in there, you'll need that!
Rotate the arm that is still attatched so the pedal is at the bottom,
Move to the other side of the bike and slide the other arm onto the axle with the pedal at the top and facing away from the frame. Thread the nut on by hand.
Grab the ratchet and tighten it tight (same weight as doing a push-up or lifting a 50lb bag of something), go to the other side, take the grey cap off tighten that arm as well. Then put both caps back on and ride in peace.