Bicycle Mechanics - Help! new kid!

hi,
i have a problem with my bike. every so often when riding the cranks seem to slip and jolt forward. They also make a cracking sound when this happens. The cracking sound varies from a barely audible click to a full blown crack depending on how much pressure is on the pedals. How can i stop this?

please help and sorry if its a silly question.

steve

There are no silly questions. If the bike's not working right, it's not working right.
Here's my advise:

Walk; do not run,do not ride the bike, but walk the bike to the bike shop where you made the purchase. If you have a loose crank arm, you do not want to strip it, so don't ride until it is fixed.

(I am assuming the bike is relatively new.). We are no longer in the prime biking season, so chances are they are not that busy. Ask if you can watch (oooo, kinky) and learn the cause and how to make the repair yourself next time. (don't be afraid to ask questions. There are no dumb questions. Either you know or you don't. No one teaches this stuff in school, so how else are you going to learn if you don't ask.)

There are several things that could be happening here. It could be a loose crank arm, but it could also be the chain slipping off the gears.

Is this a bike with derailers (shifters front and/or rear)? If so, is the chain on the biggest front gear and the biggest back gear, or vice versa?

Is the chain lubed? Is it rusty? You might want to lube the chain. Don't use WD-40.

Also, you might have a bent or broken tooth on one of the gears. Check them out.

Good luck finding the solution fast.

Jim

My guess (and it is a guess based on very little details) is that the freewheel/freehub is slipping or the pawls aren't engaging reliably due to dirt, water and lack of lube.

To me it sounds like there's some chainline issue here, which may make the chain occasionally partially derail (at the LOWER half of the chainring) and then snap back into line. hard to say.