I need to get engine work done on my 400EX because it won't start. I took it to a local dealer and they tore it apart. They said that to get it back to stock will cost $175 for the parts plus labor, etc. for a total of around $800 for everything. They suggest boring it .020 over. I want to go with a 440cc (11:1), but I have some questions that hopefully will be answered.

1. Will boring it out 0.020 over make it a 440cc?

2. Will a 440cc be more durable than stock?

3. Will a 440cc be able to hold the extra revs from a White Brothers rev box? (I put one on my stock 400 and it caused the problem with the engine because there was almost no oil in the reservoir.)

4. Should I get rid of the rev box?

5. Is a stage II hotcam a good idea?

6. Should I buy a jet kit?

7. What are some important things that I need to know before going with the 440 kit?

 

i dun't know much but here is what i know
your def gunna have to jet it.. don't buy a jet kit big waste of money go to a store and buy jets accoreding to what you do
2nd ur gunna need a exhaust and intake for this thing to breath and exhaust good... 3rd you probly should looken into buying a aftermarket oil cooler.3rd find a well known machine shop that does good work.. i have had trouble finding one but i got one up here in jersey... find one with a good feedback so they don't screw it up.... you might wanna look at getting a cam but i dunno about stage 2 because you will not have that much bottom end.. I put a stage 1 in mine it runs good but has trouble starting because the pressure relief ring not used anymore. its up 2 u.. alot of work ill tell u that much and make sure u put everything back where u found it.. one thing will cost you alot.. Good luck and anything elsei can help u with hit me up on AIM at Eitner8.. I just got done putting my 440 kit i couple days ago..

 

a .02 over bore, i belive is either a 406, or 416
A built to the hilt will not be durable as stock, And an average built 440 wont be quite as reliable, but chances are, if you build it right, you wont notice any difference in longevitiy from the stock motor.
a stock bore motor, with a stock cam will be able to rev better than a 440 with a stock cam. But building any motor without a hi compresion piston, and a good aftermarket camshaft wont yeild very much power. Yes, hotcam's build a good cam. Stg 2 is best for a 440. keep the hi-rev cdi, but ALWAYS CHECK YOUR OIL!!! Im still on the rocks as to how your rev box cause the said damage, a stock 400ex motor cant easily pull much above the stock 9300rpm rev limit, so unless you were trying to rev it out in first or second, It was a wasted investment for a stock machine. A jet kit is not needed, but you will need to rejet. Your local dealer will have everything you need for an assortment of jets, at a much cheaper price than a kit. When building a 440 with a very hi-comp piston(above 12:1) consider aftermarket head studs. Also, look into some aftermarket oil coolers, making something costom is fairly easy, but i believe, fst makes a real good setup for the 400ex.

 

Where can I find the fst kit?

By the way this is how my 400 got messed up....

I put the rev box on my stock 400. I didn't even think to check the oil, a big mistake. I had checked it the week before and it was fine. Anyway I went for a 3-4 mile ride and was pretty much pushing the 400 all of the way. I was riding the roads and I was going up a not so steep hill that was pretty long. It must have been just enough of an inlcline so that little oil was not getting to the oil pump. I believe that this is what caused the engine to fail but I believe that the rev box's extra 1000 rpm's added a little to the problem by making the engine work harder with no oil resulting in a very hot engine. So hot in fact that the exhaust was popping.

The 440 must be .120 over then right?
Does a stage II provide good low-end power?
How much horsepower am I looking at with the 440 kit? I believe that they are 28-30hp stock.

 

a stg2 on a 440 gives good power all around. If you feel as though you need some more low end punch, increase your compression.
Its hard to say what you will be making for power. It really depends on your compression, port work, carb set up. But, the basic 440(stock port, stock carb) are usually good for mid 30's for power.

 

.020 isn't anything. that would be like a 402 or so. a true 440 would be around .160 over. a 406 is .040 over. a 416 is .080 over. stage 2 is a high revver. stage 1 is more of a all around cam. the stage 1 cam does make the valves tick louder than stock though. it really depends on the type of riding you do. by the way, i have a stage 1 forsale if your interested.

 

My friend has the 440 big bore kit, stage 2 cam, bigger valves.... ported head...... 11:1 piston. all the goodies you are talkin about here. he hasnt had any reliability issues with it, and it is his race quad... and it holds its own against the yfz and 450r. If you are lookin for performance go with all the things you have listed.... for reliability.... it really wouldnt matter too much... sure, in the long run u may rebuilt it 2 or 3 more times, but if it is only for trail riding and stuf.... then u wont have too much trouble with it... get a Big Gun rev limiter. he tried the white brothers... and his got screwed up also, he went with the big gun, and no problems yet. If you are wonderin what type of power you will get out of that whole settup, his 4wheeler kept up with my raptor that had alot of performance stuff done to it, and it hung in there all thru the gears, he also had a 16 toth sprocket to make up for all that bottom end. either way u will be payin out the wazoo.... why not make it worth more... and more powerfull