Yamah Blaster

[Ryoushi]

Hey all, wondering if anyone out there knows anything about compression testing a 200 c.c. 2 stroke engine. The manual says to block off the intake and exhaust with some sort of a plate and to pump air in through the spark plug hole to check for leaks. Can you not use compression testers on these engines?

[Macgyver55]

You can still do a standard compression test and get reliable results, but only concerning the cylinder. The way you describe is commonly called a "leak down test". It basically determines the percentage of air lost to bypassing the rings. When done correctly by an experienced mechanic, more can be learned from the results than just compression, such as if crankcase seals are ok. On 4 stroke motors, its typically done to determine if compression is being lost through intake or exhaust valves or through the rings.