Another one bites the dust

all i can say is pull her down and look at her insides it sounds like a bad one but you can always do a rebuld new bearings and whatever other parts you need they are cheap and its not hard to break a engine down if you can get the jug off and its not scored it probibly isnt to bad if it is a jug for the motor isnt alot of money pulling the jug will tell you alot about how bad it is then you can check the bearings to see if one let go

I have a BGF 80cc and I've had 3 of the 4 6202 bearings (two around the clutch rod, and two on the crank wheels) fall apart of break.

With BGF, I recommend on arrival, replacing those bearings, and giving a good greasing before running it.

Are you looking to sell any of the busted engines? I always like picking up spare parts from them.

I would pull the head first and take a look at the piston and cylinder walls. I'm guessing you will see scoring on the walls as a result of whatever was bouncing around in there. From there you're gonna want to pull the cylinder, at this point you probably will realize you need at least a new cylinder and rings and most likely piston. (I would replace the cylinder, piston and rings all at the same time, they're cheap enough) The piston may be jammed in the cylinder, you're gonna have to do whatever it takes to knock it loose. By this point hopefully you will have identified whatever part that failed. With the cylinder removed check if your bottom end moves freely (hopefully it will), if so, then I would buy a new top end and give it a try. The biggest worry is that some debris made it down into the bottom end, and could recirculate back up and take out your new top end, so you might try anything you can think of to clear out any debris from the bottom end. Splitting the bottom end is a LOT more work than just pulling the jug, would be BEST to split the bottom end and be SURE there isn't any loose metal down there, but a top end is cheap enough, you might just want to do your best to clean her out and cross your fingers and hope there isn't anything down there.
If you get the top end off and the bottom end is seized or funky then you have no choice but the split the bottom end and figure out what is going on down there. At that point you would have to decide do you want to go down that road or maybe just try another motor. I think you said this is your second BGF motor that failed? Perhaps you can rip them both apart and make one out of two, or at least choose the best bottom end to run with your new top end.
Bottom line, DIG IN, the fun is about to begin! LOL

sounds like what just happened to my brand new bgf that only had 15 mins on it

The puller tool will get most things apart. For the top end you really don't need any special tools other than a torque wrench if/when you put it back together. (might be a good idea to use a click style torque wrench when assembling just to make sure you don't over torque and strip the threads on stuff, and definitely need to torque the head bolts)

The bottom end is more tricky to get apart and put back together, so I would start out with the top end and tackle see where that takes you. On the bottom end you may need something to pull/press bearings...

when pulling the rotor off, you'll sometimes see the woodruff key jump up out of the slot and stick to the magnet - this can jamb it against the laminations there & make it hard to get off - reach into the slot with a sewing needle to hold the key down while pulling

Follow norms instructions. They are awesome. I've split these engines 3 times in the last week. Now it's super easy! These engines are super simple. Take your time!

The best way to remove bearings from any small engine aluminum housing is to stick it in the oven at 350 degrees for about 15-20 minutes with carb and all seals removed. Sometimes they will fall right out or can be picked out easy enough with a small pry bar. Of course don't put anything in the oven that will burn or anything that has fuel. If you don't get too carried away you can use a propane torch if you are careful. Anytime steel bearings are pressed into an aluminum housing.....heat is your best tool to get them out if they are froze in there.

Not sure exactly what size the bearings are in these china girls, but might want to check with someone like Bocca Bearings to see if they have a high speed steel or ceramic bearing in that size.
http://www.bocabearings.com/