Hello, this is my first post. I bought a Buyang 107cc quad with a Loncin motor from a friend of mine. He told me it would run. After I found out it had a bent valve, and complained to him, he gave me my money back and told me to keep it.

So the motor had no compression at first, I removed the motor, and quickly found out there was a valve stuck open. After removing the head I figured out something had been banging around in the pison and hiting the combustion chamber as well. I got online, and ordered a new head, piston w/rings, and gasket kit.

I googled the crap out of all this stuff, and found some Youtube videos as well. I adjusted the valves, so the rockers are just barely making contact on the cam base circle, and the cam sprocket rotates (on base circle) with easy when turned by hand. I installed the piston, and rings, making sure they were in the same order as the ones on the old piston. I even alternated the ring gap location, to avoid any blow by or compression loss there. I also adjusted the timing by making sure the motor was at TDC, and made sure the cam sprocket "dot" was pointed away from the engine before screwing the cam bolts down. (so it should be set exactly at TDC)

I put everything back together, reinstalled the motor, connected everything, and tried to fire it up. nothing. I have fuel, and spark, but after hooking up my compression tester, I find I only have about 35psi of compression while cranking. question is WHY????? I'm about ready to give up on the stupid thing. I should mention that the cylinder wall was in pretty nice shape still, lots of crosshatching visible, a little typical scuffing from use, and also one scratch, that I felt not deep enough to warrant a new cylinder purchase.

please help, or this will be posted on craigslist by the weeks end!
thanks

Help is appreciated. I called a local powersports place, and they of course wouldn't touch it, lol go figure.

 

Sounds like you adjusted the valves wrong.. Maby you adjusted on exhaust stroke instead of compression stroke. or you have the timing out..

 

Did you ever get this resolved? I have the exact same problem and have tried everything under the sun that I know of and have torn it apart 4 times. Any advice would be greatly appreciated.

 

"I adjusted the valves, so the rockers are just barely making contact on the cam base" isn't adjusting them properly, no wonder he has low compression.