melted piston

[mikeric]

I just took apart my 400ex that my brother blew up. The piston is junk. The cylinder walls are also deeply scored. I was thinking the best thing to do would just be rebuild and get a 440 kit. I was wondering who makes good quality stuff, what i would need to be done by a profession, and what i can do myself. Pretty much just some help guiding my get started on the process. I have rebuilt my old suzuki quadracer 250, my old lt80, and a few ford 302s. So i have some mechanical experience, just not on 400ex motors.

[416exduner]

Most of your big shops make some pretty quality kits, just depends on how much you want to spend. Duncan and CT racing make good kits but they cost a good amount too. Curtis Sparks makes a good kit that is at a relatively low cost.

If you've rebuilt a couple of motors than you could probably handle rebuilding the top end of a 400. The only thing that you would need a shop to do is to take the old sleeve out of the cylinder and put the new sleeve in.

Hope this helps you get started...just ask if you have anymore questions.

[mikeric]

I think i might go with one of the curtis sparks kits. I want to improve performance, but still want the bike to be reliable. What would you recommend for bore size and compression ratio? Also what supporting parts will i need? A friend told me a bigger oil cooler was a must. Anything else?