Question about 2000 Harley Davidson FLSTC Heritage Softail Classic

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Harley Evo blowing oil through air filter. Isn't

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Well, there is an "umbrella valve" in each of the center sections of the rocker box. These can and do get brittle from the repeated heating and cooling. They do a good job of keeping the bulk of oil out of the air filter but they can't get it all. As will all previous Harleys, they blow a bit of oil and those that relieve their crankcase pressure into the air filter do still make a mess that must be cleaned out occasionally. But, it shouldn't be excessive. Excessive blowby on the rings can exaggerate the problem.

To replace the "umbrella valves", simply take the bolts out of the rocker box cover and replace the gaskets and the valve. You will have to pull the fuel tanks to do this job.

Good Luck

Posted on May 21, 2011


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1 Answer

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1 Answer

Oil blowing out through air-filter,rough running,engine light comes on,tries to cut off.stop then shut down for a few min. then usually runs ok till next ride.was told to clean "breather tubes,air filter...

Your '98 Evo motor is what they call a "head breater" engine. This means that the crankcase ventilation is at the upper end of the heads rather than way down at the lower end of the engine like it used to be. They the first year for the "head breaters" was 1994.

Now, At the top of the heads where the rocker boxes are, there are three pieces. The lower rocker plate with the rocker arms in it, the middle piece and the upper cover. If you take the four bolts out, you'll see an umbrella valve in the middle piece of the rocker boxes. This valve is a replacable rubber piece. Over time and many times of heating up and cooling down, they can get brittle and allow a lot of blowby resulting in oil in your air filter element.

Now there is another part in the cam chest that has a lot of effect on the operation of the crankcase breather system on your bike. This part is called the "breather gear" and is located down in the cam chest to the rear of the camshaft. In you bike, the part is made of plastic if it's the original part. I have seen the teeth break off of the drive gear and the breather gear stop turning. This will screw up the "breathing cycle" on your engine and cause it to "blow oil". Usually, the oil pump locks up when this happens due to the plastic teeth getting in the oil pump but not always. If this eventually turns out to be your problem, have the mechanic or yourself install one of the new S&S reed valve type breather gear replacements. They don't turn at all and work absolutely great. The part is about a hundred dollars but it's well worth it. Solves the old broken breather gear problem that has plauged the Evo engine it's entire life.

There are no "screens" in the Evo engine other than the "tappet oil screen". Just in front of the oil pump is a screw plug that is in the engine cases itself. If you remove this plug, there is a small spring and cone shaped screen that filters the oil prior to it going to your tappets. This should be cleaned every other oil change but it has nothing to do with the oil in your breather.

Now some riders will tell you that if you allow your Harley to sit for any length of time that it will "oil sump" with you. By this, they mean that oil will seep past the check ball in your oil pump and pool up in your crankcase. When you start the engine up, oil will be blown into your oil filter. Not true on your Ultra. The bikes that will oil sump are the Sportsters, Softails, Shovelheads, or any bike that the oil tank is higher than the oil pump on the frame. On your Ultra, the oil tank is on the bottom of the transmission. Your bike will not "oil sump" unless you have a sheared key in your oil pump or the oil has somehow learned how climb. You oil tank is below your pump in other words and oil does not flow uphill.

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