Do the Japanese manufacturers use identical engine casings, drilling just smaller holes for their 400 cc models? Can owners easily upgrade their 400s to 600 cc engines, like with a Sportster 883 to 1200 cc? Just wondering... Chris

Not quite the same as new jugs on a Harley. Was looking at doing it on an FZR400 (wanted to put in the 600cc engine). Mounting bolts are the same, but engine is not.

Much much much easier to just buy a 600cc machine. If you put a 600cc in a 400cc frame you'll soon discover that the rest of the bike was never designed to handle the extra power. More headaches than it's worth IMO. Ride On! T

I've done engine swaps and it's not to hard if you stick to the one model. It's when you decide on a different engine from another bike where it gets.....interesting!

Some of the things to watch out for if your swapping parts from one to the other:

1/ Exhaust ports and exhaust system different inside diameters.

2/ Gearbox or output spocket different ratios.

3/ Carb venturi different size or jetted differently. Inlet port/valves different.

4/ Added frame reinforcing on bigger engined bike not on 250cc frame.

5/ 250cc head on 400cc engine can raise compression.

6/ Starter motor on 250cc not powerful enough for 400cc.

7/ Brakes/rims/tyres/spokes/swingarm on 250cc to light for 400cc.

You need research on every little thing!