Need help with 440 big bore

[Wasmer]

So here's the story.

I got a 2007 400ex off a friend, when he got it he was told it had cams (no specifics), had an HMF slip on, 40 idle and 165 main jets, and it has a crappy GYTR filter on it which I plan on replacing with a new K&N, other than that, stock.

He ended up losing an oil line or something, didn't notice, and blew it up. He then bought a stock head honed out to a 440 with 11:1 Wiseco piston and rings and installed it. This is when I aquired it... NOT knowing all the details until now.

After riding it the first time I realized it was no more, or not even as powerful as my 400 I previously had. I started researching and saw on RMATV the stage 1 cam says "not reccomended for big bore" stage 2 doesn't mention it, I don't know what kind is in it. Then I saw, while googling the internet and coming across a lot of 440 nightmares, with the big bore there are other things that need done, like a larger oil tank, oil cooler, cam chain tensioner, main bolts, jets, etc. I found out he did none of this.

I want to get this done right before I ride it anymore. I've never done, or owned a big bore before. What do I need to do/add/modify to make this 440 run right with no worrys? Also will 93 octane do? I don't have race fuel near me, may just use octane booster anyways. If it makes a difference, I only ride woods.

So far these are the suggestions I've gotten, I'd appreciate it if you tell me what you think and or what other suggestions you have...

1. Head studs from GT Thunder (I don't wanna do all that if I don't have to)
2. CFM Oil tank with cooling tubes, found on ebay for $159, looks pretty nice, supposed to lower 50 degrees.
3. Add an electric fan like from a 450R.
4. Change jetting to 42 slow 180 main (keihin) 2 turns out from lightly seated on the fuel screw.

Sorry for the long post, didn't wanna leave out any details, thanks in advance!

[CJM]

First thing you need to do before any of this is to perform a compression test to make sure everything is ok in the engine. Should be minimum 100 psi, you have lower than that its time to take it apart and inspect stuff for wear or damage.

These motors dont like heat, if your friend never jetted it and its been ridden chances are it cooked itself. In the very least your jetting of 42 pilot and 180 main (or more) is needed. The GT thunder head studs are well worth it, motor gets to hot the exhaust studs pull out. Oil tanks worth it, but not 100% needed, fan is in the same boat as the tank-needed but not a dire situation (you want a spal puller fan 4" if I recall).

93 octane will be fine.

You can find out what kinda cam it is by removing the rocker cover and looking at the numbers printed on the cam.

[2001400exrida]

11:1 440ex does not run on 93 octane very well. My 11:1 is a must have 100 octane minumum, it was pinging like mad with pump fuel. I'm not sure if some get away with 11:1 on pump gas or not, but i wouldn't test it.

Personally if you want a good build that will last. get a new cylinder with a 416 or a 426 bore, this will require a new piston as well, but that's going to give you good power, without the thin 440 cylinder walls and with less heat.

on the 400ex a good rule of thumb is anything 11:1 or more needs to have a better fuel than pump gas.

[JOHNDOE83]

Deffinetly need a 180 or bigger main jet, theres is no such thing as thin cylinder walls on a 440 the sleeve is installed so that the cylinder wall is irrelevant.

440's dont create heat either, bad jetting creates heat.

You dont need heavy duty stud's, they are a good idea for any build but you only need HD studs if you have high compression.

All the jetting info you will ever need is right here www.jetsrus.com NO ONE! no one can ever give you a estimate on jetting, you have to follow the main jet tunning method in the link.

Theres stock bore 400ex's on this site running 200 main jets.

Good luck with your motor.

[tayyo789]

The first 440 setup I had was an 11:1, and after about a year, I noticed that it had gradually lost power since I had installed it. It was about as powerful as the old 400 was, even though I had a big bore, cam, and tuned properly. My problem was a head gasket, and foolishly I didn't upgrade the head studs, and ended up blowing a few more gaskets before just moving back down to a 416.
Test the compression, check out that cam, and the rest of the top end at least. It could even be as simple as jetting, but it's better to be safe than sorry. CJM knows his stuff, all the things he said are right in line with the general consensus on here. Read through the sticky at the top of the section page also, there's a ton of information in those threads that might help you out. There's definitely some gurus that have been through here.
Do you know any more about when he blew it up? It might be a good idea to check out the bottom end just to be safe

[jpresslor]

With 11:1 u can run pump gas its when u got to the 12:1 or bigger compression u need to run race gas it keeps the motor cooler but u dont have to i just rebuilt my 2000 400ex i got a 12.5:1 compression and a stage 2 hotcam my buddies dad is a pro with these motors and he uses a crf450 dirtbike cam chain they are stronger then the 400ex chain and i got a bigger oil tank from ebay for 100 buck but mine was new u can find used on there for 50 sometime and i would get a second oil cooler from fourstroketech and install that definently sence u ride woods ur motor going to get hotter sence ur not flying around all the time and u should never have to worry about blowing a motor unless u neglect regular maintnence and if u have extra cash after those to upgrades get a 04-05 450r carb with a cable then u will feel a diference hope this helps

[tayyo789]

That was the longest sentence I've ever read

[Wasmer]

Never done a compression test myself before but doesn't seem like anything I can't handle. It's only had 4 hours on the motor since he rebuilt it, ran perfectly smooth, just not feeling any faster than stock. Starts first touch of the button every tim,e no problem, I can sit on it at idle no hands and it'll crawl across a field forever and never stall. The machining/drilling/tapping whatever you wanna call it for the new head studs is what scarse me off. I'm not comfortable doing it myself, and I don't have the money to pay someone, honestly I'm still trying to find the money just for the parts. I actually have the quad posted up for sale so I could just get a new quad that hasn't been messed with. I just hate to start over, I've already put a lot into this one (combined with all the goodies I stole off my last 400ex before selling it). If I'm keeping I know the filter and jetting need to happen and I'll want to do the tank and fan also, if I'm gonna keep it I want to take all precautions, so I guess it's time I find out how I can get the studs done... Thanks a lot for the help, much appreciated, this forum has given me far more than the others I've been on!

[JOHNDOE83]

Ive had a 440ex for over 7 years now with no heat issues.

I dont have a bigger oil cooler, I dont have hd studs and never needed them.

The jetting is the most important to the 440ex, I run a 220 main jet.

You will never feel your motors true power until youve tuned your main jet properly, if the 440 doesnt seem to have any power then youve done something wrong, havent jetted it, or just dont notice it.

Buy jets that are from 220-180 in incriments of 5, start with 220 and try to go wide open throttle. If it doesnt fully rev out and stutters like a rev limiter then its to rich and you drop down to 215. keep doing this till it fully revs out, thats how you tune for a main jet.

Your 440 will run hot, too lean, wont rev out like it should, feel slow and more then likely blow itself up if you dont start using bigger jets asap.

My 440 gets raced at the drag strip against high mod 450s and bolt on banshees and will win all day long.

[Stickman400]

That was the longest sentence I've ever read

Technically it's not a sentence. He never put a period on the end!

[2001400exrida]

Deffinetly need a 180 or bigger main jet, theres is no such thing as thin cylinder walls on a 440 the sleeve is installed so that the cylinder wall is irrelevant.

Some 440's are bored to a 440, not everybody purchases an aftermarket jug, in the case of the aftermarket cylinders, the walls are thicker yes.


440's dont create heat either, bad jetting creates heat.
On the 400 air cooled motor, compression creates heat. An 11:1 440 creates more heat than a stock 400, which is why most guys find alternative cooling methods.


You dont need heavy duty stud's, they are a good idea for any build but you only need HD studs if you have high compression. if you go 11:1 with a 440, HD studs are a good idea.


All the jetting info you will ever need is right here www.jetsrus.com NO ONE! no one can ever give you a estimate on jetting, you have to follow the main jet tunning method in the link.
Actually many of us can give a good estimate on jetting, but nobody will be able to give a perfect jet size just by reading the mods, certainly we can get him close enough with an estimate though.


With 11:1 u can run pump gas its when u got to the 12:1 or bigger compression u need to run race gas it keeps the motor cooler but u dont have to i just rebuilt my 2000 400ex i got a 12.5:1 compression and a stage 2 hotcam my buddies dad is a pro with these motors and he uses a crf450 dirtbike cam chain they are stronger then the 400ex chain and i got a bigger oil tank from ebay for 100 buck but mine was new u can find used on there for 50 sometime and i would get a second oil cooler from fourstroketech and install that definently sence u ride woods ur motor going to get hotter sence ur not flying around all the time
before somebody takes your advice i'm going to correct a couple things. Sure people might be able to get away with pump fuel on 11:1. I am not able too, my motor was pinging and i'm not going to flirt with disaster. Telling somebody that you don't have to run pump based on your assumptions is not good advice. Also, higher octane is not in order to help the motor run cooler, it's needed with higher compression ratios in order to prevent detonation and to maximize power output. 12.5:1 with pump gas is plain and simple stupid.


and u should never have to worry about blowing a motor unless u neglect regular maintnence and if u have extra cash after those to upgrades get a 04-05 450r carb with a cable then u will feel a diference hope this helps
you will have to worry about blowing a motor if you're running pump gas on a 12.5:1 piston on the air cooled 400ex. Now on the liquid cooled machines the line is drawn around 13:1 for pump gas vs race gas, but on the 400ex, you try to run pump gas on 12.5:1 and you're gonna have some trouble i'm sure of it.

[Wasmer]

Looks like you guys have answered all my questions, awesome response, thank you all, hopefully I'll find a little cash soon, order the parts, and see how it all goes, love my quad, but don't wont this big bore to be a worry, determined :devious: to make it work, that is unless someone buys it first lol but so far no good offer I've got has came through, so fixed it will be!

[Blodg]

Wasmer, don't forget that there is a 3rd option here. So far you have talked about 1) selling the 440 and 2) adding HD studs/fan/oil cooler/jetting but since it sounds like you are not dead set on the 440 you could also keep the current quad and buy a used cylinder or have a new sleeve put into the current cylinder and go back to a more stock piston for probably near the same money that you would spend adding the HD studs and increasing the cooling of the 440. Just throwing it out there.

[JOHNDOE83]

Some 440's are bored to a 440, not everybody purchases an aftermarket jug, in the case of the aftermarket cylinders, the walls are thicker yes.


On the 400 air cooled motor, compression creates heat. An 11:1 440 creates more heat than a stock 400, which is why most guys find alternative cooling methods.

if you go 11:1 with a 440, HD studs are a good idea.


Actually many of us can give a good estimate on jetting, but nobody will be able to give a perfect jet size just by reading the mods, certainly we can get him close enough with an estimate though.


before somebody takes your advice i'm going to correct a couple things. Sure people might be able to get away with pump fuel on 11:1. I am not able too, my motor was pinging and i'm not going to flirt with disaster. Telling somebody that you don't have to run pump based on your assumptions is not good advice. Also, higher octane is not in order to help the motor run cooler, it's needed with higher compression ratios in order to prevent detonation and to maximize power output. 12.5:1 with pump gas is plain and simple stupid.


you will have to worry about blowing a motor if you're running pump gas on a 12.5:1 piston on the air cooled 400ex. Now on the liquid cooled machines the line is drawn around 13:1 for pump gas vs race gas, but on the 400ex, you try to run pump gas on 12.5:1 and you're gonna have some trouble i'm sure of it.


Im pretty sure all 440s are sleeved.

My 440 is also 11:1 and runs 190 degree temps, Call it a freak of nature if you must but its true.

I also stated that HD studs are a good idea for "any build" but not really needed unless you have really high compression.

Thanks for the explaination tho, I really appreciate it.....lol.

[2001400exrida]

Im pretty sure all 440s are sleeved.

My 440 is also 11:1 and runs 190 degree temps, Call it a freak of nature if you must but its true.

I also stated that HD studs are a good idea for "any build" but not really needed unless you have really high compression.

Thanks for the explaination tho, I really appreciate it.....lol.

my 426 runs 220 degrees when in the woods. How do you test your temperatures johndoe and are you testing them while running high speeds or while woods riding.

there is absolutely no question that a 440 11:1 will run hotter than a stock 400ex. I was forced to put HD studs in my 426 after a year and a half of riding so now i recommend people just do it if they're raising compression.

anytime for the explanation.

[JOHNDOE83]

LOL ok man.

My 440 after 20 mins of hardcore WOT riding will also get to 220, things get hot when they get rode....lol.

220 degrees is also what a stock 400ex will get to in the same conditions.

If im cruising on mild trails at mild speeds I stay around 190-200.

Idling with no fan or air stays at 190.

Like I said twice now, you dont need HD studs unless you go high compression. Some people will say 11:1 is high enough for studs and some people dont,I have 11:1 440 and no studs for 7 years now.

Are studs a good idea, "yes" I said that twice now also, they are a good idea for any build, Are they needed NOT 100% of the time.

If your piston is 11:1 and you got a stage 2 cam, your compression to octane ratio might vary also and might "MIGHT" not be 11:1 still.

I dont understand were the confusion is, you essentially said the same thing I did?

[2001400exrida]

LOL ok man.

My 440 after 20 mins of hardcore WOT riding will also get to 220, things get hot when they get rode....lol.

220 degrees is also what a stock 400ex will get to in the same conditions.

If im cruising on mild trails at mild speeds I stay around 190-200.

Idling with no fan or air stays at 190.


no confusion, just don't agree with everything.

Generally speaking my motor gets much hotter riding mild trails and mild speeds than it does at WOT. The engine rpm really has nothing to do with how hot the motor will get, it has to do with how much air is blowing across it. you could let the thing sit and idle and it would heat up to 220 no problem, but if you're wide open throttle down a straight you'll be cooler than you would be putt'n around through the woods. The woods are where my 426 was getting warm, lots of tight technical trails. When i'm running higher speeds the motor keeps itself a little cooler from the air blowing across.

[JOHNDOE83]

Dude, we can go back and fourth as much as you want.

I dont undersand what you dont agree with, when im running at wot I mean running at wot threw trails, on a track, or in a yard, sometimes down a dirt or paved road.

I said "my 440 in a closed shed with no fan or moving air running at idle for 30mins was still at 190 degrees".

When I say wot I mean on tight track style stuff at WOT balls out racing for 30-40 mins before I checked my temps, I ran multiple tests and rode multiple styles while checking my temps to get the accurate and true results im speaking of.

FYI on paved or dirt roads no matter how hard I ride it only gets up to a highest of 210 degrees.

Maybe your 426 is overly lean causing you to run so hot, if you havent jetted it using the jetsrus go big method then your deffinetly to lean to begin with anyway.

If you get froggy, re jet it the proper way then re take your temp readings and post the results.

For some strange reason I feel like your saying the exact same thing Im saying only your changing it and complicating it into a arguement. If you read back we technically didnt disagree on anything :rolleyes: