I have just bought a new 125cc lifan engine from eBay and I enjoyed it so than a month later a bought a 146cc bbk. 2 weeks later,I was riding not a high rpm and quad engine just locked up so I put it in neutral and walked all the way home and took off the head to find out my piston was flipped the opposite way and there was chunks of the bore everywhere. I took the engine apart and cleaned all the chunks of piston and bore out the bottom end. Went to my computer on eBay and found a cylinder and piston brand new 30$ and free shipping .it arrived a couple days later and a slapped it on and now quad won't start. I adjusted the valve clearance and still won't start and I looked at both valves and their not even closing all the way. So I guess that's why no compression. What do I do?? I did proper valve clearance 3 on intake 4 on exhaust.

 

it may be you didn't put the timing gears and chain in correctly