400ex rebuild

[fastyz85]

hey guys i need a rebuild on my 2000 400ex and i want to know what bore kit is the best for trail riding and some mx here and there where i won't have to run race gas, and still be reliable. If i do get the bore kit how much, estimated ofcourse, do you think it will cost me to get it done at the local speed shop. thanks

[Pappy]

do up a 406, it shouldnt run more then $400 complete....less if you do the work yourself

[krt400ex]

Originally posted by Pappy
do up a 406, it shouldnt run more then $400 complete....less if you do the work yourself

ya but a 406 won't give him enough power for mx.

i would do like a 426. they r still not that expensive, prolly more like $600, if u get a new sleeve, which is a good idea otherwise ur bike will get real hot real fast. u don't need to run race gas if u keep the comp. at around 10.5:1. hope this helps

[exrider008]

Originally posted by krt400ex
ya but a 406 won't give him enough power for mx.

i would do like a 426. they r still not that expensive, prolly more like $600, if u get a new sleeve, which is a good idea otherwise ur bike will get real hot real fast. u don't need to run race gas if u keep the comp. at around 10.5:1. hope this helps

a 406 will give him plenty of power:rolleyes:

i would do a 406. i just did a 406 using wiseco piston, new valves, vavle seals, and new gaskets and it was $400 and i could deff see a diffrence in power.

[DieselBoy]

how much is it for 4 valves for A 400ex?

[fastyz85]

thanks guys and ex rider how much of a diff did you feel in power
, anymore opinions?

[fastyz85]

also ex rider do you run race gas or no?

[Pappy]

Originally posted by krt400ex
ya but a 406 won't give him enough power for mx.

i would do like a 426. they r still not that expensive, prolly more like $600, if u get a new sleeve, which is a good idea otherwise ur bike will get real hot real fast. u don't need to run race gas if u keep the comp. at around 10.5:1. hope this helps

The bore size alone will do ZERO to add power from a 406 to a 416. Compression will, but not bore size.

A good cam and a 11-1 piston will run just fine on pump gas

[exrider008]

Originally posted by DieselBoy
how much is it for 4 valves for A 400ex?
i dont know i had a little head work done at the same time but the bill came out to 160 so i would gess 80-100.


Originally posted by fastyz85
thanks guys and ex rider how much of a diff did you feel in power
, anymore opinions?

i felt a big power diffrence from my stock piston/rings that were destroyed after i sucked sand in and my wiseco. but i would get a cam like pappy said and also a full exhaust so u can really got the full power out of it.

and i yes u can run pump gas. (run supper)

[krt400ex]

Originally posted by Pappy
The bore size alone will do ZERO to add power from a 406 to a 416. Compression will, but not bore size.

A good cam and a 11-1 piston will run just fine on pump gas


well then how will the bore size make a diff in power between the 400 and 406???

i don't seem to understand that

[maxamillion]

krt400ex, I believe the reason he wants a bore kit is because the motor needs rebuilt, therefore the cylinder walls are probably worn or scratched and need to bored/honed. The bore size from 397cc to 406cc is equal to 1mm over, which will not gain any noticable power. The reason people gain power from using a 406 piston (like myself), is because they also have higher compression than stock. Im still using my stock cam with a JE 406 10.6:1 piston with flexsteel gaskets and my motor feels like it has quite a bit more torque throughout the gears. Hope that helps. -Max

[EXevan91]

a 406 or a 416 with a good cam i used this guys the bore my 416 the first kit on the page is a good one u can also get a cam from him and hes in PA. http://www.advmachining.com/400EX.html

[Old Head]

I'm not getting this no extra power outta bore size. Sounds like if you get a stock 11:1 with cam it will be the same as a 416 with cam.:confused: just doesn't add up

[krt400ex]

Originally posted by maxamillion
krt400ex, I believe the reason he wants a bore kit is because the motor needs rebuilt, therefore the cylinder walls are probably worn or scratched and need to bored/honed. The bore size from 397cc to 406cc is equal to 1mm over, which will not gain any noticable power. The reason people gain power from using a 406 piston (like myself), is because they also have higher compression than stock. Im still using my stock cam with a JE 406 10.6:1 piston with flexsteel gaskets and my motor feels like it has quite a bit more torque throughout the gears. Hope that helps. -Max


i understand that. there is hardly a diff. in size and power. but a 426, stock compression, will give u more power than stock. if it didn't, then why bore it that big?? u see what i'm saying??? i know copression makes a big diff. in power, but we're talking about bore here. he said that he wants power for occasional mx and he wants good power for trails. a 426 would give him enough for mx, not a 406. that is all i was simply stating in my first post in this thread.

[Pappy]

You will see no noticable power increase from a 400cc 406cc416cc426cc as long as the compression remains equal.

It is not the bore size, it is the compression that garners an increase in power.

This is related only to bore size and keeping the compression the same along with the cam.

krt...you need to start understanding before you make claims. If and when someone steps up to a 416 or a 426 they almost always go up in compression. this is where the power increases are found. even a mild step in compression will benefit the HP numbers. people bore to 416,426,440 either by choice or because the end result of thier engine package dictates them using a certain bore size. a built 416 will be right with a similairly built 440, the same as a built 406 will hang with a equally built 416. to many people fall into the bigger is better theory and in most cases they get no gain from going much past a needed clean up bore.

[Pappy]

Originally posted by krt400ex
a 426 would give him enough for mx, not a 406. that is all i was simply stating in my first post in this thread.

incorrect. a 426 with the stock 400ex compression will make no noticable gain in power over a 406.

[wilkin250r]

There are many factors to building power. Yes, size is one of them.

Power is made by burning fuel. The more you burn, the more power you make. So, burning 426cc of fuel/air will make more power than 406cc of fuel/air.

But the real question is, does it make significantly and noticably more power? This is where Pappy is correct, it's just not going to be significant. Jumping from 406 to 426 doesn't have NEARLY the impact of jumping from 9.4:1 to 11:1.

Now, there are also other factors that come into play. When you start increasing piston size, you also increase piston mass. This can have a dramatic effect on how the engine behaves in the upper RPM range. Heavier pistons cause more vibration, inbalance, and thus do not rev out very well. However, the increased inertia helps low-end torque.

However, larger displacements do pull in more air, and increase air velocity. This will change the efficiency of your camshaft. This is why it is important to choose a camshaft that compliments the rest of your engine package and desired power characteristics.

There are definitely beneficial reasons for larger bores. If everything else is equal, a 426 will make more power than a 406. You will never see a pro rider running 400cc in a class that allows up to 450cc. But size isn't everything. A properly built 406 will run circles around a basic home-built 440, even if they are the same compression.

[fastyz85]

ok guys i think i've come to a conclusion i think im going to run a 406 with 11:1 wiseco piston, a new cam, new valves, valve seals,and maybe a full exhaust system to complete the package

[fastyz85]

thanks everyone for your help, god i love this site.

[dabensmiller]

I just got a new sleeve,440 piston and a stage 2 hot cam. It cost about 550 canadian. The guy at Wiseco said it would be just as bulletproof as a stock set-up. My EX pulls almost as hard as a 450R and i don't have it piped yet. You are best to just go big or go home.

[exrider008]

Originally posted by fastyz85
ok guys i think i've come to a conclusion i think im going to run a 406 with 11:1 wiseco piston, a new cam, new valves, valve seals,and maybe a full exhaust system to complete the package

u will love it i just did the same exact mods to my 406 about 3 months ago.
BTW: with a wiseco piston make sure u let it warm up cuz its a forged piston and it needs to expand.

[exrider008]

Originally posted by dabensmiller
You are best to just go big or go home.

bigger isnt always better... atleast thats what ur mom said:chinese:

[dabensmiller]

There is no replacement for displacment. If a 406 was so great don't you think that Doug Eishner would have won the 4-stroke nationals on that rather than his 465cc machine. It is plain logic, the more fuel burnt the fast you'll get from point A to point B.

[Pappy]

Originally posted by dabensmiller
There is no replacement for displacment. If a 406 was so great don't you think that Doug Eishner would have won the 4-stroke nationals on that rather than his 465cc machine. It is plain logic, the more fuel burnt the fast you'll get from point A to point B.

It mechanical science not logic that gets an engine running. And there is more to making power then displacement.

[Pappy]

Originally posted by dabensmiller
I just got a new sleeve,440 piston and a stage 2 hot cam. It cost about 550 canadian. The guy at Wiseco said it would be just as bulletproof as a stock set-up. My EX pulls almost as hard as a 450R and i don't have it piped yet. You are best to just go big or go home.

This is usually the end of a good thread.

[dabensmiller]

Well of course there is more to it, you want it to inhale and exhale as effiecent as possible. But a properly euipped 440 would crush an equally eqipped 406.

[buster024]

This is usually the end of a good thread.


Agreed.:grr:

Great stuff earlier though. Bookmarked this one.

[Pappy]

Originally posted by dabensmiller
Well of course there is more to it, you want it to inhale and exhale as effiecent as possible. But a properly euipped 440 would crush an equally eqipped 406.

I can agree that it could, but the thread isnt about anything you have replied to. The man doesnt want a stump pulling 440, he doesnt want a full on 426 with a cam so big it would make Linda Lovelace choke. Ofcourse noone really gives a ratts *** about what information a person wants, they just want thier 2 cents added even if it has ZERO to do with the thread.

[dabensmiller]

I am not trying to get everyone all exicted. I just wanted him to know that a 440 produces nice power and it isn't much more that a 406. If your gonna rip your engine apart you might as well get r done. but that is my opinion, i am 210lbs. so the 440 power was welcomed with open arms.

[fastyz85]

Originally posted by exrider008
bigger isnt always better... atleast thats what ur mom said:chinese:

thats hilarious exrider. i would get the 440 but i don't have enough money and i still want some low end for trails and stuff, and thanks for the info on warming it up before riding off(not like i don't do that anyway but im just saying). I think the 406 is good for now, well at least til i get my 450.:devil:

[dabensmiller]

The 440 piston was like 20 bone more than a stock piston. and it will give you more low end trail riding power than you can shake a stick at.

[exrider008]

Originally posted by dabensmiller
The 440 piston was like 20 bone more than a stock piston. and it will give you more low end trail riding power than you can shake a stick at.

just give up, he said he doing a 406 so just end the thred.

[wilkin250r]

Originally posted by dabensmiller
The 440 piston was like 20 bone more than a stock piston. and it will give you more low end trail riding power than you can shake a stick at.

Yeah, the piston is about the same price. But a 440 requires a $250 resleeve, rather than a simple $60 bore and hone.

If money is tight, a 406 or a 416 is ideal. That extra $200 is much better spent on a camshaft rather than a new sleeve. Sure, all things being equal, the bigger displacement will have more power. But a 406 with a good cam will run circles around a 440 with a stock cam.

A 406 will rev out very well. If you go with a mid-range or all-around camshaft, you're good, but if you go with a high-rev camshaft, you may also want to think about adding a new CDI with a higher rev limit.

[fastyz85]

thanks wilkin i'll put it into consideration, what stage do you think i should get stage 1 or 2. i was thinkin one. will i need the cdi with a stage 1.

[wilkin250r]

Originally posted by fastyz85
thanks wilkin i'll put it into consideration, what stage do you think i should get stage 1 or 2. i was thinkin one. will i need the cdi with a stage 1.

I'm not going to reccomend one or the other. YOU are going to be riding it, YOU are the one with a certain riding style and riding terrain.

However, I will tell you the difference, so that you can make up your own mind. As a general rule, Stage 2 runs at a higher RPM. It has better peak HP, but you lose low-end grunt. This is fine in the sand and in wide-open areas, but it can be difficult to handle if you're running through rocks, woods, and creekbeds. A stage 1 is more of an all-around camshaft, and is much more friendly in tight terrain. And, because it peaks at a lower RPM, the stage 1 typically doesn't need a high-rev CDI.

[fastyz85]

thanks wilkin thats what i thought i just wanted a second opinion.

[fastyz85]

bump