Here's the motor I made using 244 and 253 parts.
https://s1.postimg.org/25zhlaz33j/image.jpg
The head is from an AJS Regal Raptor 125 engine (DD125E) because it has bigger inlet ports than most 244 engines. I guess it's something particular to AJS because all the other 125 heads I've seen have smaller inlets. I think the 125 head on the 250 pistons makes it slightly higher compression.
The barrel is from a 253FMM that has been shortened by around 15mm to work with the shorter con rods of the 244 crank, and the pistons are YX140. I had to grind out the engine cases a little bit so the 253 barrel would fit into the Jinlun 125 bottom end. I changed the crank from a 180 to a 360 so I could use the 253FMM cam and a single PZ27 carb.
I was unable to fit a front cam chain guide so I just left it out but everything works fine.
What I end up with is somewhere around 200cc. I am currently using 428 chain with an 18t front sprocket and 28t rear sprocket on an 18" rear wheel. This seems to be about right for the gearing on this bike. I have only been using this engine for a few days but it seems to run very well.
https://s1.postimg.org/98ulmqxky7/image.jpg
