Time To Build

[Ridetrikes250R]

so i just bought a 400ex for 500 dollars, the guy was going to powdercoat the frame, go long travel, yah know... the whole gig, well he started to rip the bike down, till..... he couldnt get the swing arm bolt... with fury and frustration, he quickly did wat any perosn would do.... gave up on the project and bought a 450.... lol, 5 years later, he needs room in the garage for his rhino, and sold the 99' ex to me lol.... so its time to do this thing right, i know iam getting suspension, and i know i can afford this project, but heres my dilemma, i can get a 440 kit with stage II cam , gaskets and 12:1 piston for 379 or a 426 with stage II cam and piston for 279.... its going to cost me 125 to sleeve the cylinder or bore it, so ..... iam leanin towards 440, i am a dune rider, and the bike will be made for high speed dune travel and jumping, my quesiton is ..... the 440 worth it or is the 426 just as good.... and iam hearing alot about overheating, so what oil cooler do you gusy recommend

[TWISTED DINLI]

sounds to me like the 440 kit would be better. since it is only like $100 more IMO you should go with the 440 kit.

[GPracer2500]

Either way, don't forget heavy duty head studs.

[400exrider707]

Those "complete" kits are a joke... at 12:1 I would definitely do a heavy duty rod as well as the heavy duty head studs. The gaskets I wouldn't trust at all, so I would at least get a cometic head gasket, a new cam chain (heavy duty), and bottom end bearings. No sense in building a motor thats going to blow apart every time you ride it, build it correctly and only build it once.:cool:

I dont want to discourage you from this build, but its always good to do it right the first time and understand that there will be other things that you dont account for...

[Ruby Soho]

Originally posted by GPracer2500
Either way, don't forget heavy duty head studs.

You beat me to it:)

[Ridetrikes250R]

do i have to have a machine shop put the studs in or can i ?
Adam

[zrpilot]

Best if a machine shop does them, because they need to be straight, inline with the bore.

[Ridetrikes250R]

so you have to drill them out and tap them, or do they just go in the same place?

[GPracer2500]

Originally posted by Ridetrikes250R
so you have to drill them out and tap them, or do they just go in the same place?

They go in the same place but new threads must be created. A roll form tap is the tool for that job--NOT a cutting tap (which is the kind most of us have in our garage). Rolled threads are significantly stronger than cut threads and that's where much of the additional strength comes from. The extra strength of the HD studs themselves is only secondary to the extra strength of the new threads in the cylinder. That's the primary stud issue with built 400EX engines--the studs pulling out because the aluminum threads in cylinder can't hold up.

Unless you've got the right tools and experience, I'd have a machine shop do it. Make sure to tell them to use a roll form tap.

[Ridetrikes250R]

how much does that cost

[zrpilot]

should cost no more then $125 professionally installed.