400ex rebuild

[bodfper]

What I have planned for my rebuild is to go all out with a 440. I have a head port and polished by Duncan racing along with Duncans X2 cam and hardfaced rocker arms. Here is my plan

-have cylinder resleeved to 440
-either 12 or 12.5:1 piston and run 110 octane
-gtt head studs
-crf450 timing chain
-cometic MLS gasket set
-heavy duty clutch

I already have air cleaner and exhaust spiced up along with a secondary oil cooler.

I am just looking for expert advice on how I should go about this build and what other things to add to the build. I have heard of lightening the flywheel so it revs faster, how much weight should I have taken off? Also this machine is a 99 and has been ridden pretty hard would it be a good idea to go through the bottom end? Is my stock crank and rod going to accept this much HP or is a crank and rod upgrade needed? Another thing is that the combustion chamber in the head isnt in perfect shape and I was wondering if it could be trued up and polished along with the heads gasket surface being trued up? Lets hear what everyone has to say! THANKS IN ADVANCE

[bodfper]

I also failed to mention that I have bought a 450 carb but need to do MUCH research on where to start to install it.

[quadmanw]

Sounds like a solid build to me.. That should be everything you need to keep it cool and have a fast, powerful bike. There's probably 100 threads on here about how to make a 450r carb work for a 400ex. Zrpilot (I think that's his name) a forum member sells a part that you will need to make it work though, I know that

[CJM]

If you dont mind running race gas then thats a solid build. Remember tho, depending on how much you ride it might get expensive.

You should invest in the following to ensure its cool tho:
-4" spal puler fan mounted on the oil cooler
-Larger oil tank
-Additional or larger oil cooler. You can use either or but its a good idea if your worried about keeping cool.

I wouldnt even bother resleeving your cylinder. Go one bay and buy an entire kit from LA sleeve (iirc thats the name). Its done right and you will save the labor on everything else.

The 450r carb will usually take 1-2 jet sizes lower than your ex carb. You will also need to purchase the hotstart plunger and spring and boot and fill the boot with rtv to seal the hotstart. Your also going to need to buy ZR pilots adapter or make some plumbing adapters from home cheapo work. Also gonna need a 450r throttle cable, a 52 pilot as well. Choke is impossible to use with this carb on our quads.

Dont bother lightening the flywheel till later if you wish to do so. It can make it easier to stall and will rev up WAY to quick in some cases. Wanna do it later give it a shot.

Solid build imho. Better question tho: how good a suspension do you have? If you got a beast of an engine but no way to control the quad in the rough stuff its wasted power. I have my suspension somewhat upgraded and have more than enough power but cant always use it b/c the suspension limits me

[bodfper]

Good input thanks...I am still curious on the bottom end. Is there anything I need to do to it or should I tear it down to inspect it?

I do have upgraded suspension. I have works shocks in the front along with +2 a arms

[CJM]

Should be fine then with a good suspension. Might want to do a long travel rear shock setup-well worth it to get rid of that bucking feeling-IF you havent yet.

I wouldnt worry bout the bottom end unless you have problems staying in gear or shifting.

[bodfper]

Ok thanks for the info on the rear shock i always thought i was landing wrong when i felt the buck...I also did a little thinking and what had happened is that my bike would not start so I pulled the plug to check compression which it had. I looked at the plug and found that there was no gap so I gapped it and it fired right up...there is a reason the plug got smashed tho and I figure the piston hit it due to rod or crank bearings? Wouldnt this cause the stroke to stretch? I think I might have caught it before serious damage although there were particles stuck to the top of the piston along with the combustion chamber on the head being a little scarred up. Any idea where to start from here?
THANKS

[CJM]

Id check the rod and crank. Chances are one or both is bad.

[bodfper]

ok thanks