rebuild ?'s

[danbap]

my 400ex is going under the knife here pretty soon. it smokes really bad so when i have the engine out I'm going to do it right. I'm wondering what things are good to have done to these engine's. i have a yosh full exhaust on it but other then that and the rejet its stock, far as engine goes. I'm going to bore it just enough to clean it up. but as far as cams and such goes what should i have done. I'm going to get the head cleaned up also. ( slight polish and port). one thing i dont want to lose any low end power or reliability. so i dont know if i want to go stage 1 or stage 2 cam. and i dont know what piston to get (higher compression) but i do want to run 87 octane so if i cant go any higher thats fine. and also what about the sparks timing key? should i get that? and any other info would be great. thanks.

[jcs003]

try four stroke tech. mickey dunlap is one of the best builders out there and very reasonable.

[danbap]

im not going to send out my engine. i have a mechanic to do it just dont know what to have done to it.

[jcs003]

for high compression you will need race gas, so thats out. you could get a big bore but your not sendiing it out so you cant do that. a cam swap can put the power where you want it. port and polish is a good way to go but it is best if done on a flow bench.

[honda400ex2003]

heres what i have done and it works great but i run at least 89 octane with the 10:1. The stage 1 with a 406 to clean it up would be fine. you try to find a 9:1 piston but i dont think they make one that is aftermarket but dont quote me on that. you could do some port and polishing for the full exhaust to help with the top along with the low of the hotcam and it would run great. The bigger header on the yoshi helps with a bit more top anyway. you should be alright with a 406 and a sparks key with a lower compression application. i am not too sure on that either. Where abouts are you from? steve

[danbap]

it wil be on a flow bench. i ment i wasn;t sending it to some one else. i have a mechanic to assembly it and he will give it to his buddy to bore and do the head work to it. i didn't want to go bigbore case something should happen i dont want to have to buy a cylinder. i dont want an all out race machine just some more power. so what do you think on the cams ? 1 or 2?

thanks agian for your help.

[rob_990]

416
11:1 compression have to run premuim but you should be doing that anyways
hot cams stage 2
crf 450 timing chain
xr400head gasket
sparks timing hey

[danbap]

im by lake geneva.

i really dont want to have to run 93 octane.

[honda400ex2003]

cool, dont get 11:1 (93)or 10:1(93 preferably but can do 89). find a stock or near stock compression with is around 8:1 or 9:1. I am not sure what the actual amount is. if you can just clean it a tiny bit just get rings and clean it up. you need to see if rings will do it for you, if it is not scored bad get the next size up rings and put them in it. just make sure you hone to put the cross hatch pattern back in it so the rings seat good. I would def. get a stage 1 then and it would be set. you would maybe have to jet up a bit but not bad. steve

[danbap]

ok thanks. so im going to go with the stage 1 cam and ill look in to the piston and try to stay as close to stock as i can atleast for compression. now what about the timming key or a rev box?

thanks again.

[honda400ex2003]

timing key will be fine with that set up. i am not sure about the rev boxes never really researched them at all but you could run one if you want it wont hurt as long as you get one that does not advance your timing. since it will be done by the key. steve

[danbap]

ok ill go with a timming key. ive looked into the rev boxes before and i thought they were kinda pointless because these engines dont make that much power that high anyways so ill pass on that.

with a 10:1 piston i would have to bump up to mid grade gas? wiesco dosn;t have anything lower.

[honda400ex2003]

i would run at least mid grade gas. you are correct on the box. i think that too. but some people like them. i dont think theres anyone that makes a stock compression aftermarket piston your best bet would be rings only if you want it. you would not be dissappointed with the 10:1 though. i like mine it better but not quite an 11:1. The more comp. the better the power. look into sets of rings and oversize pistons from service honda or bikebandit or something like that with oem parts. honda may sell bigger pistons and stuff for a rebuild i hae never looked. steve

[honda400ex2003]

looks like you can get stock oversize pistons i take back my previous statement

PISTON (STD)
(STD) 205526-001 Enter 0-99 $71.29
3: PISTON (0.25)
(OS 0.25) 205900-001 Enter 0-99 $96.41
3: PISTON (0.50)
(OS 0.50) 206227-001 Enter 0-99 $98.58

the .5 over would be and 85.5 mm. i think that is a 402 since the 406 is a 406. these are from bikebandit.com for my 2003 but you can get them at any stock parts place i would say. steve

[danbap]

thanks for that. so you think that would be the best way to go so i can stay on 87 octane?



so ill get it
head port and polished
stage 1 cam
sparks timming key
stock compression just over enough to clean walls piston.

[honda400ex2003]

i guess i would say so if you really want to run 87. hook it up with a stage 1 and your pipe, the sparks key, maybe even a 450 carb and it would run great for a mild 400. i would still maybe recommend a bit higher octane with the key but i am unsure about how that all works. you can check around with the search and possibly find some stuff out about it. I think it would be a good improvement compared to a competely stock one anyway especailly if you really need a rebuild now. steve

[danbap]

ok can i run the timming key with 11:1 on 93 ?

[honda400ex2003]

http://www.exriders.com/vbb/showthread.php?s=&threadid=315336&perpage=13&pagenumber=1

this one looks pretty good. I did not read the whole thing but the start was good. steve

[danbap]

good post but know i dont know if i want the timming key some one said they had pinging with it.

[honda400ex2003]

that is why i was unsure too cause most guys are already running at least 91 octane with their setups. I would not do it if you are worried but you can ask the guys in that post what they think about what you want to do and see if they have had any experience with it. steve

[danbap]

does any one else know if ill be ok with a standard compression piston a stage 1 cam , head port and polish and the timming key?????
on 87 octane gas.

[jcs003]

Originally posted by danbap
does any one else know if ill be ok with a standard compression piston a stage 1 cam , head port and polish and the timming key?????
on 87 octane gas.

if i were you i would always run premium fuel. its a small price to pay to help your investment run a little bit better.

[danbap]

does any one else know if ill be ok with a standard compression piston a stage 1 cam , head port and polish and the timming key?????
on 87 octane gas.

[danbap]

its not the price im worried about it just the gas its self. when we go trail riding all my buddys all use 87 so then i would allways have to bring my own gas along instead of just splitting it with every one.

[brian76708]

Originally posted by danbap
does any one else know if ill be ok with a standard compression piston a stage 1 cam , head port and polish and the timming key?????
on 87 octane gas.

dude go with a 10 to 1 with the stage 1 you can still get away running 87 on that.

[danbap]

Originally posted by brian76708
dude go with a 10 to 1 with the stage 1 you can still get away running 87 on that.

ok. is that with or with out the timming key??

if it will work with out it then thats what ill do.

[honda400ex2003]

for the little bit of money it is extra for the key give it a try anyway. i would if it was me. if it does not run good take it out. steve

[danbap]

thats what ill do.

[honda400ex2003]

let us know how you like it and how it works or at least me cause i like to know for future reference, steve

[danbap]

ok no problem it will probably be a couple weeks.