Cylinder head cracked

[Leebossman84]

So I was riding the other day on my chopper bike with a 80cc motor and all of a sudden the head cracked. Took it off and bought another one. New gasket and head, but now it wont start up when I pedal. I definitely felt less compression still but I tightened her some more and it was trying to start. I played with the choke over and over but I cant quite to get her to run on her own. HELP PLEASE, I need my bike running again

 

[Tony72373]

Assuming the piston and rings are the correct size were your rings correctly offset? If ring gaps are too close together compression can be lost through the gap between the top and bottom ring. Some pistons do not have index pins in the ring groove.

 

[crassius]

did you check spark and check that plug gap is still good?

 

[Steve Best]

So, what changed? The head cracked. Why? Overheat or over pressure?
If it was overheat, the piston ring seal could be damaged (ring or cylinder). What is the compression pressure?

Otherwise, it could be an installation error of some sort.

Again, what is the compression pressure?