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Discussion Starter #1
back round, this is a 2002 400ex punched out to a 426, we took it apart because of a transmission problem, rebuilt the motor had no issues during assembly. we started the bike for the 1st time and it fired right up, let it idle for about 5 minutes, all is well, went out and rode very mildly check all the gears and such for about 10 minutes, when returning to garage found oil dripping out of the air cleaner on to the back of the bike and not a little but allot ie 1/4 to 1/2 a quart according to the dip stick, also found that the breather tank was full of oil (this is the little white tank that is mounted to the side of the intake boot) , shut the bike off and let the breather tank drain back into the motor, took air cleaner off and started the bike back up, put my finger over the breather tube and there is just a wisp of air ( so this test eliminated ring issues and blow by) checked the oil in the tank and found it to be low. also because it was a new motor we filled it out of a gallon jug so I know I put 2 1/2 quarts of oil in the motor ( bike has extra capacity oil tank not stock so this would tend to eliminate the theory of over filling engine with oil)

the only 2 things that I have been able to come up with that could cause this is,

1) scavenger side of oil pump failure or blockage causing excessive oil in crankcase.

2) damaged gasket where oil galley goes thru the case halves over the top of the breather chamber causing an oil leak directly into the air chamber where the vent tube mounts to the engine.

has anyone had a problem like this and if so what did they discover?
 

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Welcome to the forums.
What happened to the tranny? did you loose teeth on any gear? if so with these engines all being connected to the oilfrom the engine I would lean toward a piece of trash blocking an orfice or on the scavenger side of the pump I guess the best thing for you to do at this time would be to drain out the system, I would disconnect the coil to keep it from starting and run hydraulic fluid through it. it's lighter weight than oil and will aid in removing any impurities. I would find away to attach a large magnet to the bottom of the engine so you would be able to keep what restricting your flow in the base until you can completely flush the system. I think I would also bypass the oil tank too. Good Luck keep us posted.
 

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Discussion Starter #3
No broken gears no damaged bearings, the transmition was jumping out of gear, found 3 gear with slightly rounded cogs, and one worn shift fork. All oil passages were cleaned and air blown thru them, all parts were washed in slovent tank and blown dry. 100% sure that dirt, metal pieces, or debri is not the problem.
 

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I know someone that had this problem with a 300 Honda utility. It was throwing oil out the crankcase breather tube. He had just put new piston and rings in the engine and couldn't figure out what it was. He asked a mechanic at the local Honda shop. The mechanic told him that it was the timing chain and that it would cause them to do that sometimes. He sold the 4-wheeler, instead of changing the timing chain, so I don't know if that was the problem or not. I don't really see how a bad timing chain could cause that, but I'm not a Honda mechanic. I have worked on a lot of ATVs, but I don't work at a Honda dealership, so maybe he knows what he is talking about, but I don't know. Just thought I would mention that.
 

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Discussion Starter #5 (Edited)
Thanks for your thoughts, after performing a few diagnostic tests i concluded that something was wrong with the gasket where the oil galley runs above the breather tube chamber. So I took the engine out and tore in apart upon splitting the case haves I found that the gasket had shifted during assembly and the hole in the gasket for the oil galley was partly uncovered into the breather chamber. Reassemble the motor with a new gasket and all is well. just got back from Glamis and the bike ran all weekend and never spit out any oil.
 

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I have a TRX 450 R that i did a complete rebuild on new crankshaft, piston,rings,valves, and guides. Ran it after rebuild and it runs great but after about 5 minutes running oil started coming out of the crankcase vent line that goes into the air box . The motor have two separate oil compartments one is for the crankcase and one is for the transmission / clutch . the oil level is going low on the left (crankcase side) but the crankcase vent comes out the right side at the top of the engine and goes into the air box. Any ideas why this is happening ????????? Maybe crankshaft seal on right side of crank installed backwards ??? This is a real bummer Need help !!! Thanks !
 
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