"Blew up my 400EX, Lookin for possible reasons why"

most likely reason: abuse

i think the guy you got it from screwed you over. did he make you a 'really good deal'? if so, he must have had a reason...

 

how can you say that when he just ran water through the engine. does anyone in here know what happends when you TRY to compress water. that's just it, water doesnt compress. you're lucky you didn't end up with those new ultra-trick 2 piece connecting rods. [img]i/expressions/face-icon-small-confused.gif[/img]

 

Well if yout oil is contaminated then you have a water situation. If the oil is contaminated then most likely you will have bigger problems if you ran it for awhile. My buddies bike just took a drink and the oil was grey and now the motor is not cooked beyond repair. That being said, I don't think that water is your problem. It sounds more like a mechanical problem in the transmission.

If you swallowed water you would have other issues like smoking and poor running conditions. I notice you never said anything bad about the motors performance.......that leads me to think it is a flukey tranny failure. Let us know how you make out.

 

drained all of the oil out.
No water in there anywhere. Oil smelled burnt. (This is wierd cause I just changed it Saturday and I rode on Sunday) The oil also had a really thin consistency to it. There were alot of metal shavings in the filter and in the oil. Bad News. Looks like I will be ripping her down after all! I tried to run it for 20 mins after changing the oil to see if it would break free. Nothing. The shifter doesnt move at all. I am thinking now that either the shift fork slipped out of the drum, (Bad news cause it would have to break for this to happen) or the gear is frozen on the shaft and just wont let anything move.

A little more info on this, the bike starts right up and runs fine. No problems with the motor at all, only shifting the tranny!

It will probably be a few days till I can rip her apart and see but I will let you know what I find!

 

Found this thread from awhile back. I apparently never said what caused this issue....

It ended up that the seal on the sprocket shaft was bad and that's how the water got in. The water hit the hot transmission parts and that was it. Ended up replacing 2 gears and one shift fork. Hot metal parts + ice cold water = rebuilding the tranny!

Little late on the update I guess but better than never.

 

Better late than never. Glad to hear you got it fixed.

 

One of my buddy's had a problem similar, His case built up pressure because of the vent hose and popped his shifter seal out, when we stopped I noticed oil coming out of the bottom of his quad, some one had the vent hooked to a closed vent in the carb?!?! donno don't ask haha that was on a 05 trx450r, Fixed the hose and put the seal back in place and has been good ever sense.