Lookin to rebuild. help me out

[quadmanw]

I'm looking to rebuild my motor and I honestly have no clue what to do. I ride a lot of trails and the occasional gncc race and harescramble. I want to be fast in the woods but also fast when im riding with 450s. My 400 has everything on it aftermarket except for the motor. Im on a budget but its not too low. Im looking to put the time in and do it ride and make sure its dependable and is gonna last. If you guys can help me out i'd really appreciate it. thanks, Steve:confused:

[CJM]

Your going to have to remove the sparks timing key if you want to run a higher compression piston-the two dont mix real well. 10:1 is somewhat safe if you run good gas, any higher compression and its a bad day.

-11:1 85.5 or 86mm piston. 85.5 is only slightly over and 86 is 1mm over stock, it really doesnt matter unless your bore is wasted, do the smallest size you can b/c then you can bore it again if need be when it needs to be rebuilt again. I started at 416 and now Im at 426, I give it another year or two and I gotta do a 440 or do a new sleeve. Compression is power, not bore size on these engines btw. Bore size plays a small role but not an insane amount where boring it will see huge increases in power.

-Hotcams stage 1 or 2, 1 is more low/mid power and 2 is a good all around performer with a very good mid/top end gain.

-Cometic brand multi layered steel viton coated gaskets. VERY important, use stock or use cometic (better). Cheap gaskets will only cause leaks.

Rest you can copy from my signature pretty much. Understand one thing however: You dont go on a small budget if you want to hang with the 450's. Its either spend the coin and do it right so nothing else breaks or pray your budget build holds up.

Things to check when doing the build:
1. Cam chain and tensioner. The chain should be replaced regardless with a CRF 2002-2006 cam chaim, chains stretch and wear. Cam chain tensioner should be taken apart and checked for spring, small screwdriver inside it-turn the screw and let the screwdriver go-it springs back good your good to go, if not buy a new one.

2. Check the timing chain guides for wear, any wear REPLACE them while you got everything apart.

3. Check the rockers and where the cam rides for wear, excessive wear is not good-but usually is not common.

4. Its really easy to redo the topend yourself with a basic service manual and a bit of knowhow, saves alot of cash if you can do it yourself.

5. Jetting is VERY important! Do it right the first time. you can click on the link in my signature for more info on jetting threads. Start rich and go more lean as you read the plug and how the bike responds.

[quadmanw]

So you're saying that if i take the sparks key out and run high octane gas I can go 11:1 86mm and bore to a 416? or should I just bore it to 426 or 440 the first time? I appreciate the help man

[quadmanw]

with a stage two hot cam

[Stickman400]

Take the Sparks key out to run 11:1 compression, otherwise it'll run too hot. High octane isn't needed with 11:1 either, 93 will do. Bore it to a 86mm the first time and do a 10:1 or 11:1 compression piston with the Stage 2 cam. An 86mm piston is 407 btw, not 416.

[quadmanw]

I see in your signature thing that you you run 11:1 86mm stage 2 hotcam. do you like it? does it produce the power you want?

[chronicsmoke]

CJM has a reliable setup in his sig. I'd say 75% of the the mild built 400exs use almost the same setup.

I have a 10:1 piston 426cc and a ST.2 cam, +3 timing advance key, and a minor port job on mine. Its a decent setup, you would be surprised how much of a difference the cam made (ran it w/o one for a few years). That said, I'm going 11:1 and drop the +3 degree key when I do it again.

How's the power? Well if you compare it to a 450, still not equal. That shouldn't matter too much if you're just trailing though. The 450's become animals with basic mods, the straights they will have the HP, but in the tight trails you'll have the easy to use torque.

Coming from MX experience on a 400ex/250r/450r, I can take my ex through the tight sections as fast as my 450 or 250 but when it opens up, the 450 especially just keeps pulling. Still fun to chase the 450's on a 400ex though :D

[05DodgeDakota]

Yea as stated a good mild build is a 11:1 JE 426, with a stage 1 Hotcam, and some port work. If that's too much for your budget or you just need to rebuild and aren't looking for alot more power go for a 10:1 wiseco 407 with no port work and stock cam. My next build will be a 440 or larger, 12.5:1 or more CP piston, with probably a hotcam stage 3 or web cam.

[quadmanw]

So should I go 11:1 426 stage 2 cam or 11:1 440 stage 2... Or just go 11:1 416 stage 2 cam.. I need the most durable and the fastest most powerful set up

[chronicsmoke]

Originally posted by quadmanw
So should I go 11:1 426 stage 2 cam or 11:1 440 stage 2... Or just go 11:1 416 stage 2 cam.. I need the most durable and the fastest most powerful set up

I'd save your cylinder and go 416cc. There isn't too much difference between the 426/416

My buddy's 416 11:1 piston, with a Edlebrock, stage 2 cam beats my 426 with similar mods.

I'd get a 450r carb, 416 @ 11:1 bore/piston, Stage 2 Cam, port work. I realize that going straight to a 416 eliminates the 402&407cc bores, but this isnt a 2 stroke. A decent top end will last you a LONNG time before you need to re-bore. 5 years going on 6 with my 426 setup. :cool: (I went straight to 426 from stock, but as I stated, 416 would be the best IMO)

Do it once, but do it right; get the cam, get the port work to compliment the piston right off the get go.

[CJM]

Do the 416 build. The 440 while making impressive power MUST be jetted right and cooled properly with at least a fan on the oil cooler and a larger oil tank in most cases, and if you wanted to take it further you could even add an aftermarket oil cooler. For most the 440 isnt worth it.

Follow my EXACT setup in my signature pretty much but do the 416 or 407. Trust me the 10ccs wont matter and the 407 means you can bore it out again later on if need be when you wear out the bore. Also a trx 450r carb from 04-05 is worthwhile if you dont mind buying an adapter (or grinding out your airtube and moving the airbox closer to the engine-adapters easier).

Basically following my setup has yielded many people here the ideal setup of power and reliability. Is my bike 450R fast-no its not. Once they rev out and get into the higher gears they can and will pass me. Is it a huge margin-maybe 1-3 quad lenghts. Why do I like my EX over a 450-basic torque. I have GOBS of it vs a even a mildy worked 450 machine. Take for example a large hill climb I did. My buddy on his worked YFZ did it in 3rd and pinned it. I did it in 3rd also but I could have pinned 2nd instead of moderatly hittin the throttle in 3rd. In the woods I can outshine them, come out of a corner and the torque I have eats them alive-they can and do catch up but the power they have takes a bit to build up.

Ideally follow my advice as others have mentioned and you will be happy. Do not expect t beat a 450 machine unless you spend GOBS of money, bore and stroke, port and polish your 400-which imho isnt worth it at that point.

[quadmanw]

416 11:1 stage 2 hot cam Is what I'm gonna go with I think. Port work. Eventually a 450r carb. What about valve work? And HD gt thunder studs?

[chronicsmoke]

Originally posted by quadmanw
416 11:1 stage 2 hot cam Is what I'm gonna go with I think. Port work. Eventually a 450r carb. What about valve work? And HD gt thunder studs?

The studs are a good idea when you're at 11:1 compression.. People on here have said they are not necessary.. Ask yourself how much you like replacing the head gasket.. Just do simple valve maintanance.. shim, maybe a clean the valves up a bit depending on their condition.

I'd get the cam chain while you're in there.. maybe the guides are worn too, you wont know until you have it apart.

[CJM]

Oversized valves cant be used with the higher compression pistons if I recall. I think the pistons hit the valves unless everything was clearanced right.

Port work is worth it to do but not truly needed, remember everything costs money. The basic build I mentioned will run anywhere from 250-650 bucks depending on where you get the parts, who does the work, etc. Do it yourself (trust me these engines are stupid simple) and save big coin. If I was to build someones topend Id charge 35-50/hr and thats rather cheap vs a shop where it can be 75+/hr or mroe usually 120/hr!

Start with the basics, do the bore, cam, check the timing chain out (you have alot of hours replace all the parts i mentioned earlier) and make sure its jetted right. If you dont already have it, get yourself a slip on exhaust-not much is gained by running an $$$ full exhaust on these machines due to the overall design of the headers. Would a full exhaust help-maybe..just maybe you get 1-2 extra horsepower-but 300 vs 600 for a slip on vs full isnt worth it imho.

I 2nd chronics advice on the studs, couldnt have said it better myself.

[CJM]

Shimming the valves lol...remember this aint a 450r chronic :blah:

Regrinding the valves is worth it. I do it EVERY time i have my stuff apart if it needs it. All you need is to take apart the valve train-replacing the valve seals while your in there is worth it btw), get some valve grinding compound and a electric drill and go to town.

If this stuff confuses you or you dont have the confidence to build it yourself, take it somewhere to make sure its done right.

[chronicsmoke]

Originally posted by CJM
Shimming the valves lol...remember this aint a 450r chronic :blah:

Haha good eye.. Im used to 450r terminology lol

My engine tech charges me pennies to do my engines so I'll let him do the 400 when it needs something I'm not corfortable with or don't have time for. For a case of beer I let him rebuild my top-end, lol. (cost me a case of beer to port my head, install new valve seats, install new cam, cam chain, chain guide. :devil: )

Could have done that myself, but for $40..

[05DodgeDakota]

oversized vavles and high lift/long duration cams are fine, but you have to use a piston that is designed with the correct sized reliefs. But you also would need shortened bronze guides, new valve springs, and hard-faced rocker arms for big cams.

The actual tearing down and reassembly of the top end is easy. But when you send out the head to get ported, it's not much more to have the guy do a serdi vavle job as well. I paid $300 for some awesome port work, vavle seat recut, new valve stem seals, and chamber polish.

[quadmanw]

Thanks for all of the help guys. Im gonna go with a 416 11:1 with a stage 2 hot cam. Probably get port and valve work done and then see if I can get the jetting right. It seems that this is the most common rebuild in a 400 and I think I will be very happy with it. Thanks for all the help. If you have any other info or advice let me know. Thanks, Steve

[05DodgeDakota]

you decided on a brand piston yet? Make sure you at least replace the valve seals. Also who are you gonna have do the port/head work?

[Stickman400]

Also remember to remove that Sparks key when you rebuild it, otherwise your engine will get WAY to hot.

[quadmanw]

I'm thinkin wiesco... Or je or a good about 230$$ kit. And I have a guy around me that does a real good job porting and bore. Had him do it on my old blaster. Any better kits?

[05DodgeDakota]

JE is what I'm running in my 12:1 416. CP is alittle more HD but not needed.

[quadmanw]

I'm gonna run je or wiesco. I seem to be able to get a kit off of eBay fairly cheap.. any specific make on hotcams?

[Honda.rider5871]

86mm 407 wiesco 11:1- http://www.ebay.com/itm/HONDA-TRX400EX-400EX-WISECO-PISTON-KIT-040-11-1-99-08-/230703340462?pt=Motors_ATV_Parts_Accessories&vxp=mtr&hash=item35b6fd9bae

87mm 416 wiesco 11:1- http://www.ebay.com/itm/HONDA-TRX400EX-400EX-WISECO-PISTON-KIT-080-11-1-99-08-/320805488483?pt=Motors_ATV_Parts_Accessories&vxp=mtr&hash=item4ab17f4763

87mm 416 wiesco 10;1- http://www.ebay.com/itm/HONDA-TRX400EX-400EX-WISECO-PISTON-KIT-080-10-1-99-08-/320812392363?pt=Motors_ATV_Parts_Accessories&vxp=mtr&hash=item4ab1e89fab

Your gonna need a cam ,
HC stage 1 - http://www.ebay.com/itm/NEW-HOTCAMS-HOT-CAMS-HONDA-TRX400EX-400EX-STAGE-1-CAM-/320798507651?pt=Motors_ATV_Parts_Accessories&vxp=mtr&hash=item4ab114c283

HC stage 2- http://www.ebay.com/itm/NEW-HOTCAMS-HOT-CAMS-HONDA-TRX400EX-400EX-STAGE-2-CAM-/230717342929?pt=Motors_ATV_Parts_Accessories&vxp=mtr&hash=item35b7d344d1

Cometic gasket kit- http://www.ebay.com/itm/cometic-Top-End-Gasket-Kit-Honda-TRX400EX-TRX-400EX-99-/170637729570?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item27bacd1f22

That should be a good start, Theres not a JE kit listed , only one for a Standard bore, contact him though he probally has them for about $160 . You will be hard pressed to find better prices on piston kits and cams

[chronicsmoke]

I vote you get a Stage 2.. I've got one and it pulls much longer than the stock cam. I didn't find I sacrificed much bottom end if any.

[quadmanw]

I'm gonna contact that guy and see if he has a 416 kit. And I'm deff gonna go with a stage 2 cam. That should rip well in the woods and in the open

[CJM]

That is NOT the proper gasket to use.

This is the one you want, notice it appear to be made of shiny/rubbery coated metal. http://www.ebay.com/itm/190518644764?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

As for the rest, Jeff at apex racing (in the links hondarider posted) has the lowest prices and is a great guy to deal with. Wiseco is fine, JE is supposedly better but many run wiseco with no issues.

You dont need a "416 kit" you just have the cylinder bored locally by a machinist or your local dealer b/c they need to match the bore EXACTLY to the piston.

I like the stage 2 hotcam better than stage 1, stage 1 tends to trail off too much and has less usable power imho.

[quadmanw]

So I can buy the piston that just says 11:1?

[05DodgeDakota]

he means you don;t need a kit that includes a sleeve like a 440 would. You need a 87mm 11:1 piston kit: includes piston, rings, wrist pin, and cir clips. Then take it to the machine shop to have the bore and hone done to the stock sleeve.

[CJM]

Originally posted by 05DodgeDakota
he means you don;t need a kit that includes a sleeve like a 440 would. You need a 87mm 11:1 piston kit: includes piston, rings, wrist pin, and cir clips. Then take it to the machine shop to have the bore and hone done to the stock sleeve.

Correctomundo..

[quadmanw]

Thanks a lot guys. I have learned so much from this thread hahah. I know exactly what I'm gonna do now and ill let you guys know how it goes

[CJM]

Good luck!

[quadmanw]

If this setup is all done correctly and jetted properly it should smoke a stock 400 right?

[chronicsmoke]

Yep, it should.

But there are more important things than power.. (unless you're drag racing)

A 300ex with dialed in suspension will give a 440ex with stock suspension a run for it's money on an XC or MX track..

But if you're talking down the road in a straight line, you wont have an issue against a stoker :cool:

[quadmanw]

I got the suspension so it should be bad ***** hahah. I can't wait to git r done

[quadmanw]

Im gonna go with the 416 11:1 87mm wiseco kit i think. That is right, right?

http://www.ebay.com/itm/HONDA-400EX-99-07-416-11-1-87mm-WISECO-PISTON-4628M08700-/300635433963?pt=Motors_ATV_Parts_Accessories&vxp=mtr&hash=item45ff44abeb

[CJM]

Buy it from apex racing, not only is he cheaper-but if there is any issue he will take care of it asap. Ive bought countless things from Jeff.

http://www.ebay.com/itm/HONDA-TRX400EX-400EX-WISECO-PISTON-KIT-080-11-1-99-08-/320805488483?pt=Motors_ATV_Parts_Accessories&vxp=mtr&hash=item4ab17f4763

.80 over btw is 416.

[quadmanw]

yeah, im gonna buy that one. He seems to have good prices and reliability. is .80 over the same as 87mm? I dont understand that haha

[CJM]

Yes .80 is the same as 87mm.

Your going .80 over stock bore size.

[quadmanw]

yeah, that makes sense now. I really appreciate your help man. Im gonna order that piston from apex tomorrow and start this project. i'm looking forward to it