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ok i have a 2002 400ex and im kinda new to the 4 stroke scene, ive always had 2 strokes, ok heres the problem when you first start it its smokes a little the more you ride it it smoke more, the motor sounds great the power is all there, and it idles perfect "once warmed up" ive been told its my valve seals is this accurate and how hard is it to do like i said ive always been a 2 stroke guy and was always able to do the work myself and hope to still be able to but it seems alot harder in the book also besides the valve seals is there anything else i should change while I have it apart, also how long should it take to get er done, and will it hurt to ride it the way it is for one day i have a trip planned this weekend and im not sure that its a good idea thanks in advance

 

valve seals usually smoke only at start up

 

ok when i shut it off and restart it seems to smoke more as i ride, it does seem to clear up a little but does not stop completely

 

Shouldn't hurt to ride it at all.
Valve seals and guides usually smoke only on start up and sometimes at idle.
I would also guess maybe it needs some new rings and maybe throw a new piston in there too.
You can probably stay with the stock bore and only have the cylinder honed.

 

Red400EXRod hit it on the nail. Rings are going to be the issue. I would build a 416 11:1 compression.

 

Valve guides are the first thing to go!

 

thanks guys ill let you know as i get into it

 

Nice looking quad, I am building a 416 right now 11:1 compression, 39mm FCR (YFZ450 Carb), stage two cam, I am porting the cylinder head, old White Brothers exhaust.

 

Thanks its getting to be alittle more then what i expected though, anyone got a clue on how long it will take to do the hole top end after its honed? im thinking stock bore with new piston and obviously everything else new for top end

 

also i found a kit on ebay for alot cheaper then i was thinking can someone take a look at it and tell me if this is a good deal or if its cheap parts that wont last long