Piston doesn't reach top of new cylinder

[one_and_only_norton]

I just replaced my bike's cylinder, piston rings, and clutch pads and tightened everything down, but the bike doesn't work now. The compression is extremely weak, and the cylinder is probably the cause (piston rings were installed properly, clutch was re-adjusted). I think the cylinder is bad - am i right?

This is at the piston's highest point. i'm holding the cylinder down

 

[Tony01]

Sounds like an improper combination of parts as well as possibly many other problems. You give us no information on your setup. What did you start with? Did it run? Why did you start changing parts?

 

[one_and_only_norton]

Sounds like an improper combination of parts as well as possibly many other problems. You give us no information on your setup. What did you start with? Did it run? Why did you start changing parts?

It's a regular generic 80cc amazon motor. I first put it on an old mtb and it was great (30mph on stock sprocket, idles, everything is good) but i heard that aluminum frames could suddenly snap so I moved the motor to a steel cruiser.

I got a new cylinder since I stripped a carburetor screw (my fault) and new cluch pads since I read that black & white ones are stronger than the stock "eraser" pads.

 

[Venice Motor Bikes]

It's normal for the piston to be slightly below the deck height... (but yours does seem a little too low).
The only way to fix it without buying new parts is to machine the deck height down a little.

 

[one_and_only_norton]

It's normal for the piston to be slightly below the deck height... (but yours does seem a little too low).
The only way to fix it without buying new parts is to machine the deck height down a little.

ok I see. I'll get an orbital sander and start decking

 

[Venice Motor Bikes]

ok I see. I'll get an orbital sander and start decking

I wouldn't use a sander... The surface needs to be perfectly flat when you're done or you'll have constant head gasket problems.