Looks like you have a good project quad for a great price! If your piston broke at all, or even the piston ring **** off, more than likely there are chunks in the crank bearings. If you have the motor out, like Dutch said its worth it to replace the crank bearings and seals and check the condition of the crank. Trust me there is nothing more frustrating than strong your engine all together just to have to take it back out and completly apart. I know getting it back up and "running" sounds great but taking it slow and doing it right might have the best outcome.

Even with a flushing of the crank area you most likely will not get everything out, I'm just trying to help you in the long run. These motors are extremely easy to take apart and reassemble. There are also lots of guys on the site here that have already or will answer any questions along the way. If you have any further questions or want to chat pm me I like talking quadracers.