Rebuild Questions

[legacy400ex]

My question is how hard is it to rebuild a 400ex. I am wanting to do a 426 piston and stage 2 hot cam. I know i will have to take the cylinder to get it bored and honed but other than that it should just be assembly right. I mess with 4 cylinder cars alot, but this will be my first atv engine to rebuild. How hard is it, or would i be better off taking it to a shop?

[northwest Texas]

You can do it. Just buy a service manual. It's not difficult at all.

[zrpilot]

Originally posted by legacy400ex
My question is how hard is it to rebuild a 400ex. I am wanting to do a 426 piston and stage 2 hot cam. I know i will have to take the cylinder to get it bored and honed but other than that it should just be assembly right. I mess with 4 cylinder cars alot, but this will be my first atv engine to rebuild. How hard is it, or would i be better off taking it to a shop?

I'd use Colby at C&D and over bore to a 416. You are probably going to want heavy duty head studs for reliability. Next you will want a cam. The Hot Cams stage 2 would be a nice cam to run. I'd think about a heavy duty cam chain ($30 from servicehonda.com). You will need a slip-on muffler, HMF is a good choice. Lastly, you will want to open up your airbox.


Building a motor is like making a cake, all the RIGHT ingredients come together to produce a great tasting cake. $$$ spent on big valves, porting / polishing, milled heads, ETC without a bigger carb and a full exhaust system will not yield desired results. These types of mods may actually hurt performance unless they are all done together!

For a reasonable amount of money you can build a 400EX to make HP numbers in the mid-low 30s. For a whole lot of money, you can make a 400EX make HP numbers in the low 40s... is it worth it???? Your call...

Read some more about others experience/builds on the exriders boards. Ask questions. Keep in mind your riding style and needs. Start saving some $$$. Tear your 400EX apart to see what your working with. And lastly make a build sheet that outlines the build. You'll know what to do....

good luck

[legacy400ex]

My manual should be here tomorrow so i can get started. I also forgot to mention that i have a white bros full exhaust, edelbrock card, and tc rev box. Thanks for the help

[jordan_m6]

Its pretty easy, once you get it apart you will wonder why you were so worried, well I was atleast. After the second time it will be like changing your oil.