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2004 YZ250F Dry sump?

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Hey guys! I feel maybe I had misunderstood how dry sumps work... can you enlighten me please?

I am deep-servicing a 2004 YZ250f and I was told it has a dry sump (it seems the oil is stored at the front of the frame) and yesterday I went to check the valve clearances on the engine. When I opened the cover that exposes the crankshaft nut, pretty much all the oil in the bike drained. Funny thing is that the manual doesn't state draining the oil is necessary (no other youtube instructional videos does say it either)

Is this supposed to happen? Was it maybe overfilled? I honestly don't know what went wrong.

Thanks!

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Yes, it is a 'dry sump' however, when the bike sits, the oil tends to back flow into the engine. On start up, the scavenge pump fills the oil tank and the feed pump lubes the engine. There is a check valve to minimize this but over time, they tend to not be effective.

If a lot of oil cam out of the port, you may have it over filled. When draining the oil, the must first do the frame tank then the residual in the engine.

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@William1 sorry I didn't reply earlier, day got super busy... thanks for the clarification! It had me confused. 

There is a good chance the bike was overfilled, I bought it last year but never actually rode it. Just put it in the garage awaiting for a good session of maintenance. The bike though old, wasn't ridden much and it sat neglected in the previous owner's garage for many years. Cylinder compression is very good and the spark plug was clean, so I'm not disassemblying the engine. Everything else is being overhauled. 

Thanks again for explaining, I'll be careful when I refill the oil, just so I'll add the right amount.

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Overfilling definitely can be an issue for owners that don’t understand the dry dump arrangement. As William1 mentioned you must drain the oil at both locations. Problem is you can’t check the oil until you run the engine for a minute or two since the dipstick is in the frame tank and it takes a few minutes for the scavenge pump to get all the oil into the frame tank. When they only drain the frame tank and pour in the listed oil capacity there is no way to verify oil level until you crank it up again and see it’s overfilled. As long as you understand the system it’s easy to deal with. Clay

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