My bike pedal has just fallen off - the whole arm, and there is no obvious way to fix it! The bike is a Viking Downtown Shopping 16'' Ladies bike. Help!

This can happen if you do not make the pedals tight enough when you first install then. Contact the manufacturer or seller. They should carry the crank arm. Note that it takes a special tool to replace a crank arm. Most bike shops have crank arm pullers for sale. You can contact the manufacturer to see which crank arm puller is required. When you install the new pedal, make it very tight.

If it is the pedals it is a seized bearing and a new set of pedals will resolve. There are only two diameters is pedal threads, see a local bike shop if they are 9/16” or 1/2”.

If it is your crank arms you will need to open the machine up for further inspection

To remove the crank (the arm the pedal is attached to), you'll need a special tool. I got mine at a bike shop. (Bike shops are our friends.) I use the Park Tools CWP-7. It's pretty much a big bolt with a smaller bolt going through it. You'll remove the cap covering the spindle bolt (if it hasn't fallen out already), remove the bolt that holds the crank are onto the spindle, then thread the "big bolt" part of the tool into the threads for the cap on the crank. You'll then screw the inside bolt into the big bolt, which will push the crank arm off of the spindle.

I would just stop by a welding shop and have them weld the pedal arm on. You can buy another whole bike for what it costs to get a helicoil like that done. If it's the left hand thread, impossible.

There's a special tool called a "crank puller" that has to be threaded in to the crank arms that are on your bike in order to remove them. An inexpensive version of the tool will cost around $10- which is about the same price as a shop would charge you for the work.
If you *do* want to remove them yourself, please be sure to thread the crank puller in perfectly straight and very, very carefully (backing in all the way out and starting over if you encounter resistance). Once you have threaded it almost all of the way in to the crank arm by hand, grab an adjustable wrench and tighten it down before you spin the handle to push the arm off of the bike. (If you fudge it and damage the threads inside the crank arm, you will have to pay a shop to bash them off instead- another special tool is used for that.)

It's not the dissimilar metals.

http://www.parktool.com/blog/repair-help/pedal-installation-and-removal-pw-3-pw-4-pw-5-hcw-16

For the ladies model you need an adapter bar to make it like a mans model. , mens, you just set arms on the bike's top bar and bungee it or if it has straps use them. Make sure that your pedals do not scratch your trunk by either buying foam pedal blocks or wrap and tape them. Put the womans bike on first.

All depends on if you stripped the crank arm, you may have to replace your crank arm if you rode with a loose pedal. Pedals are sold in pairs, and there are 2 sizes, a one piece crank is 1/2" and 3 piece crank is 9/16", take your bike to the bike shop and they will tell you if you need a new crank arm or not. It will do no good to just replace your pedal if there is a bad crank arm thread, it will not hold.

Bike pedals can be a little tricky, but most likely for that bike you will need a 9/16's wrench. There should be some flat surfaces inboard of the pedals between the crank arm (the long arm that you screw the pedals into). Now, here's the hard part - the R pedal is normally threaded, but the L pedal is reversed. The easiest way to remember which way to turn the wrench is to stand behind the rear wheel and you will always pull the wrench towards you to loosen. Depending on how long the pedals have been on, they might be pretty tough to get off. You could use some penetrating spray (like Liquid Wrench) and let that sit for awhile. Also, once you get the pedals off, remember to put a little grease on the threads so that next time they won't be so tough!.