Harmonic Balancer
 

So i got a tool to install the harmonic balancer and when i was tightening the nut and the bolt and the bolt broke. the bolt was still moving but i have a piece in a spark plug that stops the crank from spinning...so now i dont know what to do

I don't quite get the picture. Did the bolt actually snap or did the threads strip? Where you using a piece of a spark plug to jam one of the pistons from moving?
If the bolt actually broke and you can't somehow grab it and back it out, it will have to be drilled out. This could be a big problem if the bolt was hardened, requiring reverse rotation carbide drill, and a way to center the drill on the bolt. Jamming a piece of metal in piston to keep the crank from turning is a bad idea, as it could damage both the piston and the head.

i got a part from autozone that goes into the spark plug and stops the piston. Its a top dead center stop bolt. i have that in the sparkplug hole and i got the broken bolt out but i cant find the 3/4 -24" bolt that goes into the 7/16th-20 adapter that installs the harmonic balancer