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98 Yz400f oil circulation issue

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Hi guys, I have been noticing an issue that I need help with.  This bike has a steel frame with an oil reservoir built into it.  I have noticed that every time I would check the oil at the dipstick after running it for a few minutes it was as clean as the day I put it in.  After about 5 hrs of riding, I knew there must be an issue with the system.  The book says the whole system holds 1.5 quarts.  I drained out about 2/3Q or 600ml from the engine and that's all that came out and of course, it was slightly dirty as it should be.    Does anyone have any ideas on why the oil isn't circulating back up to the "holding tank"?  Do the oil pumps on these things go out?  I looked for pinched lines but they all look good.  Ideas?

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So you're saying the oil that came out of the frame "holding tank" was clean as "new"?
While the oil that came out of the crankcase was noticeably different?

The oil filter housing holds quite a bit of oil, so unless you disassembled that, you'll likely never get the full 1.5 quarts out.

I'd fully disassemble the oil filter housing (right side of engine behind exhaust) as well as the oil strainer. (located on bottom of oil tank)
Make sure you don't have any blockages there, and make sure the filter is clean.

From there, fill the bike back up and run it for a 30 seconds or so, then with engine idling slightly loosen the oil gallery bolt leading up to the top of the engine.
There should be a noticeable amount of oil leaking out of that connection as soon as you break it loose.
(this is what feeds the top end of the engine)

If not, then you either have a blockage somewhere or something is wrong with the pump itself.

Edited by Michael Cahill

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That is exactly right.   I will look into those.  The filter at the bottom of the tank, does that just unscrew from the bottom of the tank where the oil line comes out?

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Actually, you can put the filter in backward IF the bike has an aftermarket oil filter cover with a letter "R" on it.  The OEM cover has a tab built on that extend through the output hole in the end of the filter.  The Ready Racing filter cover does not, so the filter can be reversed.  The hole in the end of the filter goes outward toward the cover.

Having said all that, it is extremely doubtful that you rode the bike 5 hours without oil circulation.  More than extremely.  It's a dry sump system, and oil feeds from the tank, into the engine, drains to the sump, and gets sent back by way of the external oil line that runs up the left side of the frame.  If you run the bike with the oil cap off, you'll see oil being returned just under the filler cap on that model.  A steady stream after a cold start, then once the return pump catches up and clears the sump, it will become irregular and in spurts; the return pump outruns the feed by design.  

The oil in the tank looks cleaner because you're looking at the top of it instead of the dregs.

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