I am a proud owner of a 2001 400ex ,but i want to bore it out to 440 are there other things that you have to do as in keeping the motor cool etc. ? I am going to buy the kit and am not sure if i need to buy anything else.can you just trow a 440 kit on a stock or almost stock 400ex?

 

If I were you I wouldn't go 440.... I have heard a lot of bad stories about those blowing up.... I would go 418 or 426 and put a good cam in it, open up the intake and exhaust , jet it etc.... Cooling on a 400ex is hard because it is mostly air cooled not much you can do there maybe an aftermarket oil cooler.... But again I have heard a lot of bad stories about the 440, bigger isn't always better when you go to big it just destroys the reliability....

426 with good cam and high compression you'll be very happy...

 

thanks that helps a bit .i never really looked in to the 426 i will do that thanks again.