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anyone rebuilt a 400ex? runs great but leaks oil everywhere

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Old 02-19-2012, 06:03 PM   #1
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anyone rebuilt a 400ex? runs great but leaks oil everywhere

I have an 02 400ex thats pretty nice, it just leaks oil like crazy!

it cranks up perfect, runs perfect, and doesnt smoke except for a few seconds right after I crank it every now and then, not all of the time.

I ride it pretty hard and im interested in making it a little faster.


I do EVERYTHING myself and was wondering how hard this would be to complete?

Also Ive seen a bunch of diagrams online from when I rebuilt my kx125, anyone have one for a 400ex?


thanks for any advice/help
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Old 02-19-2012, 06:05 PM   #2
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Quote:
Originally Posted by nmcqueen280 View Post
leaks oil or burns oil?
really....?
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Old 02-19-2012, 06:06 PM   #3
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leaks oil. I have a homemade skid plate on it and it traps a lot of it, plus it runs down all over the head/jug/everywhere
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Old 02-19-2012, 06:10 PM   #4
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Quote:
Originally Posted by slodc4 View Post
leaks oil. I have a homemade skid plate on it and it traps a lot of it, plus it runs down all over the head/jug/everywhere

Is the oil coming from the crank case overflow? It an easy motor to rebuild just need to know how to set the timing.
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Old 02-19-2012, 06:11 PM   #5
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since im in there replacing all of the gaskets I figured I would go ahead and change out the piston for a wiesco 11:1 or little higher compression. This quad had A LOT of aftermarket parts on it when I bought it, so im not even sure what cam/piston/bore size it has now
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Old 02-19-2012, 06:12 PM   #6
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the leaking can be more than likely fixed with a good gasket. i would order a big bore kit and have it machined. the kit will come with everything you need to rebuild it and it will include all new gaskets. this will fix you wants and needs with one kit. you will prob have around 800 in the total job. i done my 400 ex 2 yrs ago and after it was all said and done the total was 796. and some change. but i only put quality parts in it
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Old 02-19-2012, 06:12 PM   #7
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Quote:
Originally Posted by atvlifestyle View Post
Is the oil coming from the crank case overflow? It an easy motor to rebuild just need to know how to set the timing.
it could be. I know for a fact that there is oil leaking from the head...but it could be leaking from there too. What would cause it to leak from the overflow?

thanks
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Old 02-19-2012, 06:13 PM   #8
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Quote:
Originally Posted by cball917 View Post
the leaking can be more than likely fixed with a good gasket. i would order a big bore kit and have it machined. the kit will come with everything you need to rebuild it and it will include all new gaskets. this will fix you wants and needs with one kit. you will prob have around 800 in the total job. i done my 400 ex 2 yrs ago and after it was all said and done the total was 796. and some change. but i only put quality parts in it

i thought about doing the big bore, but it gets really hot around here and i dont think it would last long with overheating a lot
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Old 02-19-2012, 06:20 PM   #9
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Quote:
Originally Posted by slodc4 View Post
it could be. I know for a fact that there is oil leaking from the head...but it could be leaking from there too. What would cause it to leak from the overflow?

thanks

Sounds like you only have a bad head gasket. I just wanted to make sure you didn't have a cracked case or jug.
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Old 02-19-2012, 06:24 PM   #10
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Quote:
Originally Posted by atvlifestyle View Post
Sounds like you only have a bad head gasket. I just wanted to make sure you didn't have a cracked case or jug.

Oh yea also make sure that the head studs arent the problem or you will just blow another head gasket. you should use HD studs if you are modding the motor.

Lets see some pics of the quad.
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Old 02-19-2012, 06:28 PM   #11
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I have done many rebuilds on the 400ex, it's a easy motor to work with. Here's a couple I did for Atvsource.
http://www.atvsource.com/articles/pr...roll_415ex.htm

http://www.atvsource.com/articles/pr..._rcr_400ex.htm

The 416 kit gave the best results.
Sounds like the valve cover is leaking or a valve adjustment cap leaking.
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Old 02-19-2012, 06:39 PM   #12
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^NICE write-ups



is there any disadvantage to just using a standard bore higher compression piston?
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Old 02-22-2012, 03:29 PM   #13
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As long as you build everything around your HC piston you'll be ok. Remember that with higher compression you'll have to run 91+ octane fuel. The 415 or 416 kits are best if your needing to bore. Don't go to 440 unless you want to replace cylinder on the next rebuild.
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Old 10-17-2012, 09:41 AM   #14
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If it is blowing oil out the over flow it most likely is because u have to much oil or the bike is getting to hot.
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