well i just got done tearing my 400EX apart for rebuild, was buring oil. when i got the cam removed i found that it was a hot cam, but i dont know how to tell what stage it is. i dont have the tool for the valve spring compression tool to look at the valves and valve guides but when i got the piston out i found out where it was burning oil!!!! one side of the piston was all black. my question is 1. how do i tell what kind of piston it is, so i know what kind i should replace with/ or just replace rings. 2. i can get the whole kit on ebay 402 kit with all gaskets wiseco piston for 150 and just have it re bored at the shop and leave the head as it is without tearing it apart and looking at the valve guides and valves.??????

 

You don't say what year your 400ex is but I would recommend getting a new piston, the kit you mentioned, and take the piston and jug into the shop and have it bored for that piston.
You can also drop off your head and have the valve guides replaced if you want. Probably not a bad idea.
Then all you need to do is reassemble the engine and adjust the valves and you're good to go!

 

its a 2000. do you know how to tell what kind of piston it is? i cant find any marks on it whatsoever. does that mean its stock piston??

 

also, should i replace the cam chain? or do those usually last a long time???

 

It doesn't matter what piston is in it now if you are going to replace it. The shop that you will take it to, to have a bored will mic the new piston and bore the jug to that size.
It wouldn't hurt to replace the timing chain but it isn't always necessary. But on a 2000 I would replace it.

 

ok thanks for the help, where can i get a halfway decent cheap cam chain?? as far as the valves and valve guides go, im going to find a valve spring compression tool on ebay i guess so i can do the work my self. do i need the valve guide reamer or can i use something else to get the soot out/replace??????????

 

from what my local machine shop told me, you donot have to ream the valve guides out unless your going with bigger valves then u must ream the inside of the valve guide out, if your valve guides are worn, then u have to ream the outside of them out, a local machine shop can help you with this, ive rebuilt my old 400ex engine several times and a cam chain heavy duty one is a good replacement for preventive maintience, cause if your stock chain stretchs you will throw timing off and thats never a good thing,

hope thsi helps

 

ok, but my kit came with new gaskets for the whole top end including valve guide orings. so i might as well change them to prevent any further burning of oil. if the valve moves freely in the guide can i just change the orings and tap them back in????

 

im not sure about the valve guides moving up and down and what the clearance should be, replacing seals can save u trouble down the road, but i would get a machine shops opion on the valve guide clearances

 

if its blowing oil...take a socket, any kind. like a spark plug socket and place it on top of your valve RETAINER and smack the top of the socket with a rubber malet. your valve keepers will fall out and you can get to your valves. do this to your exhaust valves. willing to bet your seals are bad, or cracked or the holding spring is off/loose. if you have them off might as well do the intake and replace them too. remember when you put the springs back in, you MUST put the tight wound end part of the spring DOWN. look at it from the side. you"ll see what i mean.

timing chain... YEAH, i would replace that every 1 1/2 years or 60 hours. thats will make a 400ex tick so bad, its anoying. got to take it off in this order. clutch cover, then clutch springs, then clutches, then the basket. after this you can take the nut off that has the chain on it. remove from there.