I bought a 167FMM CG250 (233cc) Chinese copy engine. I’d like to use it in my recently completed silver CG125 but as the old CG125 is 6v with points ignition and the CG250 is 12v with electronic ignition I don’t much fancy changing the wiring harness and all the light bulbs. So I have been investigating swapping the crankshaft and cylinder, piston etc to some spare CG125 crankcases I have. The first issue is the crankcase cylinder opening size isn’t big enough to accept the larger cylinder liner, so today I set about boring the crankcases to accept the bigger liner.
All posts by andrew
CG250 to CG125 internal swap investigation
I had a look to see if the 167FMM CG250 crankshaft and cylinder will fit into Honda CG125. Cylinder opening in the crankcase will need machining and I think the main bearings will need changing.
Shakedown Run Completed
Fixed small oil leak from the rocker cover, tightened steering head bearings, adjusted front brake, dialled in the idle mixture on the carb. All sorted.
The CG125 is street legal
I had the day off work today. Got my CeeGee through compliance and then decided to further investigate swapping the Chinese CG250 internals into Honda CG125 cases. Got quite a long way in when I discovered the main bearings are different sizes. Gave up and put it back together. I’m so chuffed I bought a small Makita impact wrench. Made the process so much faster and easier, although I did have to get my air one out a couple of times on really tight things. I didn’t know but square number plates are now a thing ?
Another CG125 Finished
All ready for compliance and new number plate next week.
The CG250 Engine Lives!
And it lives 
I was beginning to despair. Turns out the wires from the stator were in really bad shape where they went through the grommet on the engine case. I cut them, soldered them back together and shrink wrapped them.
Looking good
Almost done :-)
Got the crappy Chinese carb sorted, was full of swarf and had a pinched bowl gasket. Strip, ultrasonic cleaner bath and reassembled and it’s running good now 🙂
Decals on
Got myself some nice vintage style decals for my new CG fuel tank. No bubbles ??
Engine installed
Engine painted
The engine came up pretty well in the photos, not quite as nice in real life. I used a wire brush on electric drill along with a small brass wire brush, then degrease, pressure wash then 400 grit wet and dry. Pressure wash, dry with compressed air, heat gun and paint. Lockdown achievement accomplished 🙂
And it’s a roller
Starting to make some decent progress.
