400ex 440 kit or not.

[YamondaEX]

I have a '99 400ex with a stock bore and it's time to rebuild it. I've heard that some guys have had problems with the 440 kits so I don't know if I should bore it out .020 or .040 or just go full out with the 440 kit. I know one problem is overheating and I already have the air scoops so how much would that help with the overheating? What are some other pro's and con's on this decision? Also, how hard is it to change the cylinder sleeve?

[TwentyBelow131]

Go with a 426 with stage two cam and a higher compression piston. It will rev better than the 440. And you wont have to worry about any over heating.

[YamondaEX]

Do you have to change the sleeve to do the 426 kit or can you just bore it .120 over?

[mills_racing]

go 440 i love mine....i mean come on u have ta go big bore now adays since the 450's is out and the over heating problem i have never had and i dont have scoops jus wats in my sig.

[YamondaEX]

its obvious the 440 has the most power, but i need something thats dependable and i can ride anytime without needing to worry about something. some people say it has heat problems, some say it doesnt. im thinkin either the 426 or 440.

[JukeU25]

well i had mine tore down and was debating what to do and i just put a 10:1 wiseco piston in and called it quits... but im no expert and im not trying to tell you whats what but all i heard when i asked people is go 416.. i dont know why they just said it runs so much smoother and stronger...but good luck

[thrasher_ex]

id go with the 440......THERES NO REPLACEMENT FOR DISPLACEMENT

[nowukno]

I think the 416 puts out great power and is more reliable.

[vinson581]

^^^ im seconding the 416 reliable an with good porting a stage 1 or 2 hotcam, and the 11:1 piston with the C&D gasket the bike will rip

[RidrKFX]

go with the 440 kit cause ex's are slow and need help bad :devil:

[vinson581]

but your kfx isnt any quicker and nothing to brag about.....a built 400 will run from a kfx....

exriders.com

hence the name ex or trx400ex

now i see you have KFX, that doesnt equal EX so why are you hear to bash 400ex owners.

just remember a 400 can own a yfz on the track, because its like 30% bike 70% rider, and thats a fact.

[trx416m]

Go with the 440 i love it and i race harescrambles and have never overheated. Same with a friend of mine. the last race was in 90+ degree weather. never had any problems or heard of anyone having any. 11:1 compression by the way on 93 octane gas.

[Bigun55]

Go with the 440.. thats the next thing im gonna do 2 mine

[underpowered]

i say go 426. you can buy a big boar sleeve, start out at a 426 and always go up to the 440 if you want. i love my 426, get power, quicker revs than a 440, but not that much less power. I have had very few problems mine, mainly headgaskets.

[rippin2]

416..never had a problem and i hang around with my buddies 450r

[400exrider707]

Would someone care to indulge how a 416 or 426 is going to rev faster than a 440? Is it just because the piston itself is acutally heavier? There are way to many variables to say that a 416 or 426 is going to be faster than a 440. If they each were modded right out and one was a 426 and the other a 440, how could a 426 possibly be better?

[F-16Guy]

440 kits have a bad reputation because of the crappy kits that people buy on e-Bay, and then install themselves. If you want to get a 440 kit, do it, but do some homework, too. You will need a good machinist to bore the cylinder squarely for the new sleeve. He'll also need to machine the head gasket surface, and you should also have him deck the cylinder (make it shorter, so that when the piston is at TDC, it will be closer to the top of the cylinder). This is so you have the proper compression ratio and squish area, which is the space around the outside of the piston which, if set up properly, will force all of the fuel/air mixture towards the center of the combustion chamber for more efficient burning as the piston reaches the top of the compression stroke. Read through this thread; there is a hugh amount of good information:
http://www.exriders.com/vbb/showthread.php?s=&threadid=8316&highlight=deck+the+cylinder
Everyone that is thinking about doing a 440 kit should read this first. Good luck!!

[4everhonda]

I have a 406ex, If you take a stock piston out and get a 440 with the same compression as stock, you wont really notice the difference just slower revs. You get all your power from the compression and how it get air/fuel mixture into the motor. valvejob and port job with good carb will make more of a difference than 40 cc's. The best is to get atleast 11:1 compression

[ZSK]

Originally posted by YamondaEX
but i need something thats dependable and i can ride anytime without needing to worry about something. some people say it has heat problems, some say it doesnt. im thinkin either the 426 or 440.

If you need the most reliability then stick with a .01 or .02 overbore. The problems with these "kits" are that they are not either installed properly or they wear out every other component in your engine.

My 440 was built to be a woods motor and it was a great one. A simply modded yfz (pipe, filter) was dead even in a short drag race and pulled the same out of the hole. I could get the 450r by just a bit. You won't get the 450r or yfz450 type power with a cheap simple little kit. It'll take a lot of effort and money to get the reliability and power from the 400ex.

My engine cost just over $2000 to build and I did it over 2 years. It started all stock with simply one of the kits and a slip on pipe. About $500 in machine work and the cost of the kit yieled a Ross 89mm bore, resleaved, machined cases and high compression piston. After about 40 hours it started eating headgasket. FDO HD headstuds were installed at just under $100 with machine work. It ran fine for another 40 hours until it started smoking and ticking/knocking loudly. A rebuild was in order. HD cam chain, cam chain tensioner, new hotcam, valve springs, valves, rings and rockers, and good full exhaust system came out to about. About $900 in machining and parts. Ran fine for roughly 12 hours before destroying the clutch and 3 gears. Add another $600 in parts, Basket, pressure plate, center clutch, stiffer springs, fibers, and steals. After this final build it dropped the intake valves and took out the piston, crank, cracked the rod, valves and springs. It cost me $6500 this time. I finally said **** this and bought a YFZ and love it. I sold many of the parts and returning it to stock displacement for reliabilty. It has cost about $600 this time, buying a complete bottom end, top end etc.

You have to also take in account the time it took for all of the engine work to be done. Each tear down meant a new gasket kit which are in the $40 range. It's not cheap or easy to maintain a built motor like that.

[ranger400ex1994]

a 440 kit really wont add that much power unless you get it done right with all the good stuff like ZSK said. the 40 extra cc's don't add the power the extra compression adds the power. i would go with either a stock bore 11:1 compression piston or a 406,416,426, 11:1 compression piston. with a good cam. also head work is the key to power. a good port job is well worth the money. personaly the only 440kit i would do would be from a motor builder like TC or sparks. or a stroker 440 is really a awsome motor.