Well I did this conversion to a buddy of mine. There was definitely a very noticeable Hp gain. We have another of this scoters here and we tested before and after the 57mm BBK.. The compression with the 52mm cylinder was 150+ psi and with the 57mm BBK the compression is 170 psi now. I'm going to build mine now but as I said I milled 0.7mm of the top of the cylinder. The cylinder, not the head. I'm looking to achieve a little more compression. I really don't care about efficiency as the 95 octane gas here costs something like 50 cents a gallon.
Thx for the warm welcome guys. I'm from Venezuela. I do my own upgrades on my bikes. Actually I'm just installing a 57mm BBK on my 125cc scooter. I took the cylinder to the shop and milled 0.7mm of the top of the cylinder. I'm going to install that on Monday. I did that to the cylinder, not the cylinder head. I checked the clearance between the piston and the valves and I seem to have enough clearance there. Not a lot of valve adjustments here. I like to add a dab of loctite to the threads of the valve adjusting bolts. And in fact I am going to start motovlogging. Ill share here a couple of vids of mi scooters once I get my action cam in the mail... I bought a Mobius FOV camera.
The pic on mi avatar is my favorite scooter. That's a skyhawk made by Haojue. It is not a Chinese scooter but a Japanese one. and Haouje is owned by Suzuki. It is a very good scooter and it is very well built. So far I hit 60 miles an hour (measured with my Garmin gps) and I am installing a 57mm BBK on this skyhawk. Ill let you know how it went