Fresh compression test data CY 36cc

[Polar_Bus]

So I've run about 1 tank of fuel heat cycling my new engine (dam this takes FOREVER ! ). I thought I would do a compression test on my engine and post the data for others to reference. When you do a compression test it's a good idea to set the throttle to wide open to allow max air to enter the cylinder. It took me 4 pulls and my engine reached maximum psi at about 100-105 PSI. Now I have a baseline for top end maintenance moving forward. Most of the 2 stroke motocross engines recommend you change the piston ring after 10 hours. These engines only use a single ring design, and i'm sure the quality is crap so once I see a drop in compression or I seem to have trouble tuning / poor top end performance I can just do a compression test and it will tell me the condition of the top end. My compression may come up a little bit as the rings take a set but i'm guessing not much. Lastly if you do observe low numbers, say 85 psi , try adding some oil into the cylinder and re test. If your compression numbers jump up then you now know you have top end issues.

 

[1Coopgt]

Your Compression is actually a little higher than what you are seeing . Depending on your fuel mix ratio it will raise your compression ratio . The 2s oil helps to seal the ring to the wall when running.

 

[Polar_Bus]

For my engine break-in i'm running a 25:1 ratio. I actually have some "wiggle room" to play with dome squish. I tested my squish and it was .035". That's a pretty generous number. The target squish is .010-.020". I used a Rovan fiber base gasket which measured .040" . I ordered several different size copper gaskets from DDM. Think i'll experiment with thinner base gaskets and see how they work, and how that affects my compression psi.