Mods for 300ex/350X !

[Rusty91o]

I am looking into buying a 350X top end for my 300EX. But Im a little skeptical if this will work, but most people say it does, so I have a bunch of questions that I hope somebody can help me with. Do I need the whole top end to do it? or will just the cylinder and the piston be ok. Will a 300ex head fit onto it? It looks like it actually will. Also, will a 350X swingarm fit on my 300EX? And, Is any type modification required for this to work? Any help is greatly appreciated.

[Rusty91o]

I also noticed that on the 350X head, it has 2 header pipes. I don't now if his would clear one of the frame support that the 300EX has right near the motor, by the header pipe.

[2muchquad]

Yes the 350x head can be made to work but i think you would need a big bore kit so the valves would clear the cylinder.Mine is 86mm so theres room for the valves to open.You'll need to use a timing chain from a 85 atc 250 "big red" as its the same length as the 300ex chain but its wider to fit the 350x cam.The 350x chain is too long.You'll have to make a custom pipe to clear your frame,i used a extended 400ex one.Yes there is a lot of "hear say" online about what works and what doesnt but i have personally did this in the past. Since the stock 350x is 81mm bore,i would think you would need a 330 kit(80mm) or bigger to have room for the valves.