300ex topend on 250x

[ZSNOW]

can i put a 300ex topend/crank on a 250x? i want to keep the kickstart and i already have a 250x motor. so can i just buy a 300ex topend and crank and put it on my 250x bottom end or were the trannys differents?

[Kickstarts-suck]

The top ends are interchangeable (same bore) but the bottom ends are not.

I think the bearings are different or something with the crank. ( Been a while)

Only big difference between the motors is the 300ex has a longer stroke. They have the same bore. So you should just run a 250x motor if you want the kickstart.

I have an extra cylinder if you need one.

[ZSNOW]

is the 250x motor as fast? or will the short stroke hold me back?

[bwamos]

In my experience, the stock 250x motor is faster than the stock 300ex motor.

The 300ex motor has a bit more torque down low, but the 250x has a better all around power curve.

[ZSNOW]

but is the 250x motor gonna be faster when its built?

[bwamos]

It depends on what you are looking for.

What's your class requirements.

In the 300cc Sport class 250x 300cc big bore is gonna smoke a 300cc 300ex. In the 350cc limit, you are dead even because they are both stroked and bored. Except the 250x will be about 20lbs lighter and the 300ex will have an e-start that is barely strong enough to crank the motor at a full charge.

IMHO, the 250x is a much better platform.

[ZSNOW]

300cc limit. so 250x it is. :D