So I have a 2005ish Suzuki 50cc 2 stroke quad. Wasn't running right with around 80 psi of compression. Decided to do a top end. Put on new head, cylinder, piston, rings and gaskets. Get it all back together and it won't start. Plenty of spark and fuel. Checked compression and it's now 60psi!!! What did I do wrong. I've done other top ends, but never a 2 stroke. Seemed straightforward, but I obviously did something wrong. Any ideas?

 

Be sure the problem wasn't faulty oil seals on the crank in the first place. Did you get the rings with the gaps against the pegs as you slid the cylinder on? Can't remember if the 50 has a right way and wrong way up for rings, the LT80 does. Finally, aftermarket cylinders often don't have the ports chamfered and a new ring catching a sharp port edge, can break the ring.

 

I checked the crank seal previously and it was fine. I had the rings against the stops on the piston. I couldn't see any difference in size or any markings on the rings to determine what order they went in. I guess I'll have to pull it apart and check for broken rings.

 

OEM or china top end?

 

China

 

Just checked the manual and rings do have a right way up. 6.5 ftlb torque for head bolts and diagonal tightening. All bets are off regarding compression on a Chinese rebuild kit. Though, to be fair, Linmax and Necht copies of LT50s seem to be fine.

 

Just wanted to update this post. I ended up spending the extra money on a Wiseco piston and rings and it went together smooth and runs great now. I've always had good luck with Chinese parts in Chinese motors, but I guess they don't play well with Japanese motors!