Welcome nucuda,
You can learn a lot about motorized bikes from here.
Hello - I am thinking of purchasing 2 motorized bikes... 2 running bikes for $100.
Seems good price and a nice winter project to fix up.
If they both run for $50 each, might be worth it, if just for running examples and spare parts.
Whether or not there is enough there to make a
good MB for less than just building an all new one remains to be seen.
Depending on how it was built and operated you might just be buying used sandpaper.
In short, worn out.
Those bikes have had engines on them and not well taken care of by the look in the pic, but it certainly could be a great winter project stripping out the engines and rebuilding the bikes.
The engines are a different story.
It is usually better and cheaper to just buy a new engine than parts to completely rebuild a really wore out one, but if you want to know how a typical 2-stroke goes together this is a pretty good video animation.
[video]https://youtu.be/sYcbPD5r-0o[/video]
As a beginner with time to kill I'd say it worth it to get your MB your feet wet.
Should you decide to go with the new bike to build on, I urge you not go with a Huffy Cranbrook despite where you live ;-}
Good luck!