Differences between XS250 and XS400 engine.

[Ollie]

Hi, I have a spare XS250 engine (IU5-109227) and I'm wondering what parts are interchangeable between the XS250 and the XS400? I think I read somewhere that the bottom end is completely the same but the barrel, head and carbs are different? Are there any other changes between these engines?

Cheers, Ollie.

 

[drewpy]

the crank is slightly smaller so may get a bit more vibration. apart from what you've mentioned, the pistons and rings are bigger and the valves are larger too.

 

[N8Bishop]

I've read in another thread that the 250/360 crankshaft is over 2lbs lighter than the 400. If one were to swap out the 400 stock crank, the vibration would obviously increase (as stated by drewpy) but would it harm the engine at all? Decrease longevity or cause other issues that haven't been brought up? If not it seems like a cheap and easy way to get better throttle response and drop a little weight... just seems too good to be without more drawbacks...

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[drewpy]

you can get the crank rebalanced with the pistons on, but that will cost £100.

it all depends where the secondary vibes kick in.

 

[Ollie]

Cheers, I was just trying to list some stuff on eBay and didn't want to mislead anyone

 

[N8Bishop]

Drewpy, would the rebalancing reduce overall vibration and move the 2ndary vibe point? Anyone actually tried this mod?

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[domains]

whats better, lighter crank?

for theses motors

 

[drewpy]

lighter cranks are for racing, so if your planning on riding a bit longer than a race, I think it is better to stick with the standard crank and enjoy the ride.

there will always be vibration, its a matter of where it is along the rev range and where you constantly ride it.