300ex/250x super motor

[rockingon24_7]

I am new to the atv world but have been around dirtbikes for a while. I bought a 300ex that needs a motor overhaul soon and know a guy with a 250x motor cheap. Is there a way to combine the two motors for more hp. Like a bottom end from the 250 and top end from the 300 or something like that. And if so how much power gain should i expect in percents.........thanks for your help

[CDCHONDAS]

The difference in cc's would be that the 300ex has a longer stroke, so really you wouldn't get anything there by swapping anything

[zeppelin]

like he said the cc change is from the 300 haveing a longer stroke, so the bore is the same, and incase you arewondering the crank is not easily swappable, the cases are very different, try doing a search in this and the 350cc and under forum for some more detailed answers, btw i would still get the 250's motor and a bore kit for it 'cause it is suposedly fatser than the 300 when modded (im guessing because the 300 has a longer stroke and revs slower :confused: )

[bradley300]

your right, the 250 is faster because of the shorter stroke. anyways, all the parts in the top end will swap except the piston, the pin is in a slighly different spot (i think you can usea 250x piston in a 300ex, you just need to adjust the squish to compensate)

[bwamos]

If you want a motor swap.. look at a 350x motor.

Otherwise just look at boring, compression, cams, etc.. all the usual stuff. See the 300ex buildup thread for some starters.

[rockingon24_7]

I have heard the 350x motor swap before. Did the motor in the 350x only come in the 350x or is it the same as the motor in the 350 foreman. Any help would be great

[bwamos]

Completely different motor. The 350x motor looks a lot like the 400ex motor.

[bradley300]

from what i have heard, the 250x/300ex motor is much more reliable, especially when modded. something like the 350x dosent have cam bearing or something crazy?? it was something that i never would have thught a motor wouldnt have

[bwamos]

Hmm.. I haven't heard that one.. but definatley worth looking into.

[2muchquad]

something like the 350x dosent have cam bearing or something crazy

yup,its true they dont have cam bearings as the cam itself rides in the head.i wouldnt say they arent reliable though.if they are taken care of they can last a long time.i have a 86 motor that still runs to this day.its sitting in the corner of the garage but it does run:)

[prepracing]

I have heard you can put a 350x topend on a 300/250 bottom end but I have never seen it done. The 350x motor actually fits in the 300/250 frame pretty easy, only the top motor mount takes some minor modification and the other 2 bolt right up.

[2muchquad]

I have heard you can put a 350x topend on a 300/250 bottom end but I have never seen it done
yes you can,you just have to drill a oil return hole in the 350x cylinder so it matches the hole in the 300ex case.i had both motors side by side looking at them.:)