It sounds like your stroke is fine, I have used a 2K160 Airpot cylinder set with about that stroke and about that much displacement chamber size. I used skateboard bearings for the crank but I removed the cage inside and removed all but three balls from each ot the bearings (I used two)I run them with light oil and no seals. I also used bearings for the connecting rods where they connect to the crank. For them I used 4X8MM R/C car wheel bearings (about 3.50 at the hobby shop) I took out the seals with a pin and washed the grease out with brake clean, used light oil on them too. Your flywheel could be a bit too light for the size engine you have. Mine used a 6 inch aluminum 1/8 plate and I added four golf club stick on weights to it's outter rim (that did help) I'm thinking CD discs are too light and not enough mass at the outter rim. Disc flywheels work but it's best to have more mass at the outter rim than a plain disc. The weight is more effective there. Reduce your friction and I think you will have it.