400ex rebuild Q??

[400exboyz]

i have a 2003 400ex and it is starting to smoke so i plan on rebuilding it soon. i want to bore it so i was wondering how far i can go and still run pump gas? should i also change the cam? if so what cam should i get? anything else i should change/do?

[ridein'red7]

doa 416 10:1 comp ratio n hot cams stage to for trails and playing around or hotcams stage2 for mild track and hrad playing around do a 416 so u have one more bore on it

[flyboy1294]

Originally posted by 400exboyz
i have a 2003 400ex and it is starting to smoke so i plan on rebuilding it soon. i want to bore it so i was wondering how far i can go and still run pump gas? should i also change the cam? if so what cam should i get? anything else i should change/do?

You can do a 440 and run pump gas- bore size doesn't mean everything. It's more your compression ratio that determines the necessary octane.

You should do either a 416 or a 426 as a first bore so you can always go bigger. I would do 11:1 compression: it would give you better performance and still allow you to run pump gas.

For better performance you ought to go with a cam. Stage 1, or Stage 2 Hotcams are both great choices. Stage 1 gives crazy low end power, Stage 2 is more mid and higher RPM power. Do you have a full exhaust and filter already?

[JOHNDOE83]

About having more bores....?

Alot of 440 kits come with a new sleeved cylinder, you still have a stock bore extra cylinder after that, if the 440 blows, you just re sleeve it and get a new piston.

440s are ALOT faster and ALOT more powerful then 416s or 426s, you just have to tune it right.

My vote goes for 440, you will just want one in the end anyway.

[ridein'red7]

not dis agreeing but if the bank is tight ten i wouldnt do a 440 bc u need the head studs

[JOHNDOE83]

Not true, Ive never had HD studs and never had a problem, theres a few others on this site that will tell you that studs arent even nessescary for any build in these motors.

416s, 426s and 440s are all close enough in price anyway.

[ridein'red7]

iv heard some do and some dont i would do it if it was a 11:1 but anything higher i would do the studs for safty but i was just throwing it out there beacause im building my 400ex and dont no what bore t odo i think its just gona b a 416

[400exboyz]

Originally posted by flyboy1294
You can do a 440 and run pump gas- bore size doesn't mean everything. It's more your compression ratio that determines the necessary octane.

You should do either a 416 or a 426 as a first bore so you can always go bigger. I would do 11:1 compression: it would give you better performance and still allow you to run pump gas.

For better performance you ought to go with a cam. Stage 1, or Stage 2 Hotcams are both great choices. Stage 1 gives crazy low end power, Stage 2 is more mid and higher RPM power. Do you have a full exhaust and filter already?



I have a pro circut t4 slip on, choke removed, and I think it's a stock air filter.

[flyboy1294]

Originally posted by 400exboyz
I have a pro circut t4 slip on, choke removed, and I think it's a stock air filter.

Depending on your riding style, a Stage 1 would probably suit you well. You ride trails and recreationally, I assume?

[400exboyz]

I'm thinking about goin with the 416 but idk if I want to do 10:1 or 11:1 or witch cam. I do alot of trail/hill climbs and some times dirt drag so I would like to have more top end than I do now. So witch set up do y'all think would be best for the way I ride? Srry bout all the Q this is my first 400 build.

[flyboy1294]

Originally posted by 400exboyz
I'm thinking about goin with the 416 but idk if I want to do 10:1 or 11:1 or witch cam. I do alot of trail/hill climbs and some times dirt drag so I would like to have more top end than I do now. So witch set up do y'all think would be best for the way I ride? Srry bout all the Q this is my first 400 build.

IMO you should do 11:1 no matter what. You can normally run pump gas with it, and it is a lot 'snappier' than the 10:1 or stock.

I'd grind your header welds down and run a Stage 2. It's a nice cam.

Oh! Also the Sparks X1 cam is suppose to be nice. It's more pricey than Hotcams, but it is in-between the Stage 1 and 2.

[400exboyz]

Also were is the best/cheap place to get these parts?

[JOHNDOE83]

ebay

[flyboy1294]

Originally posted by JOHNDOE83
ebay

+1

Also, you're going to need to get new gaskets/seals. Cometic makes the best stuff. Do yourself a favor and stick with them.

And finally, you'll need to replace your came chain. You can get a CRF 450 cam chain and it will fit no problems. It's much thicker and stronger than the stock one.

After that you should be good to go.

[400exboyz]

Will I have to re jet my carb?

[flyboy1294]

Originally posted by 400exboyz
Will I have to re jet my carb?

Yep in a major way. But it really isn't that hard once you do it the first time. There is a lot of useful info on this site about doing that very thing.

[400exboyz]

Okay. Thanks for the info everyone

[redneck000384]

Just to give some insight I just got finished with mine, I went wiseco 88mm (426) 11.0:1 piston, stage 2 hotcam, stock stroke hotrods crank and crank bearings along with a cometic 89mm gasket kit, and a dynojet stage 1 and 2 jet kit, and doing it myself I was in about $750 final cost with replacing all the crankcase bearings and having the jug machined. I am still in the breakin process and am waiting on my CFM oil tank to come in. Just playing around in the yard running no more then 50% throttle and keeping the revs low I can tell it has some power and thats with a stock pipe. Still have a slip on planned and will get it dyno tuned this winter.

[eotrx400ex]

i disagree about the cometic gasket, yes they are good gaskets. but i went with TUSK and was pleased with the quality. the head gasket is a nice 3 layer metal,the rocker arm cover gasket is also metal. quality was just as good as the stocks. and the kit came with all the o-rings, tensioner gasket as well. all for around $17+ s/h. i think cometic is over priced IMO.

[flyboy1294]

Originally posted by eotrx400ex
i disagree about the cometic gasket, yes they are good gaskets. but i went with TUSK and was pleased with the quality. the head gasket is a nice 3 layer metal,the rocker arm cover gasket is also metal. quality was just as good as the stocks. and the kit came with all the o-rings, tensioner gasket as well. all for around $17+ s/h. i think cometic is over priced IMO.

Nah, I think we're agreeing here. Cometic also utilizes the 3 layer metal gasket style; this makes it much more resistent to heat and shifting than traditional rubber gaskets. Tusk sounds like the same thing, just cheaper. :cool:

[eotrx400ex]

Originally posted by flyboy1294
Nah, I think we're agreeing here. Cometic also utilizes the 3 layer metal gasket style; this makes it much more resistent to heat and shifting than traditional rubber gaskets. Tusk sounds like the same thing, just cheaper. :cool: exactly why i disagreed with going with Cometic and go with TUSK an save some $$ for basically the same gasket;) :p :D