400 ex rebuild

[Rancher2005]

i have been posting some shotty posts but now i got all my questions together



1. what is a 426 bore size
2. if i go 426 do i need to put a different cam in it
3. my one exhuast valve is burnt or bent but it is pitted and like charcoal gray will try to post pic. what is my best bet for valves cheap but good


before i took my bike apart it was ticking real bad even after i adjusted my vavles to factory spec . It ran fine just smoked one decel and start up but the ticking was not right when i tore it apart i saw the valve nothing else looked worn or damaged


any help is good thanx

[01boneless]

1. sorry been so long i cant rember?:confused:
2. dont have to but a stage 2 hotcam complements the setup well :cool: remember to remove the srping and decomp pin with a hotcam
3. just get new oem valves and springs. i have seen to many kibblewhites fail make sure to mic the guides if the valve was bent the guide could be rounded out ofr. make sure to have new valve seats cut to match the valves.and make sure well go ahead and replace the timming chain with a crf450 chain its cheap insurance.
make sure if you bore to a 426 to get hd head studs a spal fan and (try if budget allows) a over size oil cooler. make sure to satgger the ring gaps and file the gaps to fit. and the best pistons are wiseco and JE. 11:1 is border line on pump gas. crank should have a tiny bit of side to side play but not a ton. should be no noticeable up and down play or wristpin to rod play. only use cometic MLS gaskets the paper ones they have SUCK!! mls only!with the 426 you will have to bump you main jet up a little richer.
Hope that answers some questions for a while :D if you have more thats what us members are here for. (god knows how many questions i used to post everyday :blah: )

[Rancher2005]

Thanks man i know it sounds shotty but I am on a real tight budget if I go 416 would I have to do head studs and I was only looking for like a 10.1piston weisco well if i am doing it i might as well do it right I am just a broke a@#


And all i do is woods riding

[01boneless]

ive been in your spot before is it stock bore right now? if so just go 402 with a 10:1 wiseco . and valves and gaskets and be done with it. lookin at like 250.00 for all of it. but yes with a 416 i recomend hd studs but not with a 402 or 407

[Rancher2005]

What is the bore in mm oh a 407

[01boneless]

a 402 is 85.5mm a 407 is 86mm

[atvrider13]

Your ticking problem could have been your cam chain tensioner. They make noise when they take a crap. They dont hold adaquete tension on the cam chain slide and cause the chain to slop around causing ticking. And /or the tensioner itself will tick

[CJM]

Ticking can mean:

1. Improperly adjusted valves
2. bad cam chain tensioner
3. Bad cam chain (usually goes hand in hand with #2)

Now, an EX will tick abit-nature of the best-but if its really loud and you dont have a hotcam your probably going to have to replace the cam tensioner, chain and guides in most cases. You can check the tensioner, remove it and take a small screwdriver and wind it-should spring back good-if not buy a new one. Chains 50 bucks if you buy an 02-06 CRF450r cam chain (stronger and its the same length but thicker).

FWIW: Dont try and do a budget build, replacing everything is key to longevity, I had a friend that found this out the hard way b/c he bought USED cam chain and tensioner and didnt replace the guides-it failed again after a short time and we had to R&R it all with new parts.

Heres a breakdown of what you probably will spend:
1. Piston, wiseco -110-140 bucks. Run a 407 bore (85.5mm iirc) and do 11:1 and run 93 octane
2. Cam tensioner, honda -60
3. Cam chain CRF450R, honda -50-60
4. Cam chain guides, honda approx 75 iirc (ones MUCH more $$ than the other, dont replace them unless yours are worn)
5. Gaskets, cometic (better than stock) approx -40
6. Bore job at machine shop, dealer or whatever approx 60-100
7. Hotcams, buy on ebay from user apex racing (jeffs a GREAT guy and many I recommend to him are SUPER happy) approx cost 125

Remember, in the end the quality of parts you buy does matter to a degree. Id budget myself for approx 400-500 bucks for all of it to make sure you have enough cash to do it the right way should something break.

[01boneless]

^^ do it right the first time like cjm said. and cjm i think 85.5 is 402 and 86 is 407 you said that in the cc's sticky off wisecos site :D

[05DodgeDakota]

clean up the vavles before you start buying replacements. Mine looked exactly like that too but the pitting was in the carbon build-up, not in the steel. You may have to clean up the seats. And replace the vavle stem seals while your in there.

426 is a 88mm bore i believe.

No you don't have to run a different cam.

run at least a 10:1 if not a 11:1 piston. Compression is where the power is at!

[Rancher2005]

Thanks a bunch guys I am new to this whole thing and u guys helped a lot I think I just want to save up and do a 426 I will let u know .My guides have very little wear on them so I don't think I should have to do them but if I go 426 I willhave to do head studs right ? And I don't know much about the valve thing either but i will try this is what they look like

[05DodgeDakota]

The head studs are cheap insurance. Only really needed on high compression builds, 11:1 and up. Bore size doesn't affect them any really. GT thunder makes as does ARP sold through Hinson. Will add about $100 to your build cost.

[Rancher2005]

If i do heavy duty head studs do the have to be drilled and tap or is the thead the same for both

[Stickman400]

They have to be drilled and tapped. GT Thunder does it for an additional $50 if you ship your cylinder to them.

[05DodgeDakota]

yea the whole point is that there is more thread for them to grab in the cylinder. Any machine shop can do it for around $50.