has anyone had this problem with there 400ex??

[atcmoto]

i recently got this 400ex, it runs great, doesn't smoke. but it has this problem. after riding for a few minutes it starts pumping oil out the crankcase vent tube. here's what i did so far, but it hasn't helped. unhooked vent tube from carb boot and pluged hole in airbox boot. did this cause the oil was trying to foul the plug. changed oil and filter, cleaned filter in the oil tank, cleaned screen in the motor, pulled and measured oil pump as manual said to do.it's good, cleaned entire oil system checked all lines for clogs. this motor has a new cylinder and piston at stock bore new rings all installed properly. has a hotcam with no decompression . any thoughts?? the faster i ride the more it comes out. im stumped

[trailrider894]

Could be a seal thats gone out... I would like to dare to say valve guide seal or something along that line? i could be wrong...

[atcmoto]

ok thanks, i didn't change valve guide seals. i just did a quick check to see if the valves were seating and they were. but that makes sense that a valve guide seal could have failed. i did do a slow break in with a full tank before i rode it any faster, so i'm pretty sure the rings seated in fine. i don't think its compression getting past the rings.

[togup]

Are you sure there is not to much oil in the motor?

[atcmoto]

ya the manual says the exact amount of oil and the proper way to put it in , in two steps. thanks though

[trailrider894]

Originally posted by atcmoto
ya the manual says the exact amount of oil and the proper way to put it in , in two steps. thanks though


did you put in 2qts? just making sure.

[atcmoto]

im up for any suggestions , this motor was shot when i got it. a slight amount of compression could be getting past a valve guide seal just before the valve closes. thats my thought. this is the first 400ex motor i had apart and im up for any suggestions

[trailrider894]

if the compression rings didn't get properly broke in, they could also be shot and causing the crankcase to gain pressure. Check your oil first then tell us...

[atcmoto]

i pulled the valve cover vent while running and no oil was coming out. i pulled a valve adjusting cover off and started the motor for a very short time just to make sure i was getting oil to the head, and it was. i agree no riding until the problem is solved

[atcmoto]

i'll get it , i'm persistent. even if it means completely rebuilding it. thanks

[rubbersdown]

Dont want to get involved in or in-between any arguments but the way I see it...Your crankcase is definitely getting pressurized. If the valve guides or seals were leaking the bike should smoke a bit. Also even if the valve guides or seals were leaking the only way for any extra pressure to be pressurizing the case would be if that pressure got passed the rings which would mean either way the rings didnt seat right. My suggestion would be to pull the head and cylinder, hone it and re-ring the piston. While the head is off just spend the extra $100 and put new valve guides and seals in also. $150 total for rings, hone, and guides/seals and no matter what the problem is/was it should be fixed.

[atcmoto]

ya i agree, im gonna pull the head and cyl off, hone the cyl , check my ring end gaps and replace as needed. measure the guides and replace as needed and install valve guide seals. should fix it