OK so this gets complicated.

Here are some things I have discovered recently while tearing apart the 125, 150 and 250 twin engines and making engines for my bike.

The engines I've been using are 244FMI (Jinlun 125), DD247E (Regal Raptor), and 253FMM (Quadzilla quadbike engine).

I've already made an interesting engine by putting a shortened 253 top end on a 244 bottom end and it ran very well.

The 244FMI crank can be taken apart at a machine shop and turned around to make a 360 degree crank, which I prefer as it means I can use a single carb for simplicity. The head is also interchangeable between the engines, but the 244 has 18mm inlets and the 253 has 22mm inlets. This may or may not make much difference in real terms. The 253 cam fits any of these heads.

The 247 (150cc) head I have also has 22mm inlets, so you can put a 150 head on a 250 engine and that raises the compression but keeps the bigger inlet size.

I've discovered that CG200 six spring, widened clutch insides will fit in both the 244 and the 253 engines, giving a nice strong six plate clutch.

I have made an adapter to use both the 244 and the 253 clutch baskets which are exactly the same size but only differ in the center bit, but my adapter means I can use any of these now.

I discovered that the valves and valve springs are identical in both engines. However, the 244 (125cc) uses a shorter cam chain than the 253 (250cc) because it's altogether about 15mm shorter. You need to use the correct rocker cover on whichever head you use because the 253 has a bigger head even though the bolt pattern is the same.

I discovered the engine cases themselves are also identical between the two engines so in effect you can put any internals into any engine cases between the 244 and the 253 as long as you remember to use the short barrels with the short crank.

Now I've been taking gearboxes apart because I was attempting to make a different gearing by using parts from the 244 and the 253 gearboxes mixed together. So far I have discovered some slight differences but some parts do interchange so now I am looking for information about the gear ratios of the individual gears so I can decide what to use.

Other than certain bearings and clutch differences there's not that much difference between them so I should be able to make a hybrid gearbox, but I can't find any information about the actual gear ratios of each gear for the 244 and 253 engines.

Any information?