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[JoeSDE]

So riding my Evo softail custom today, I have a hot flash on the back of my leg only to realize the dipstick tank plug is out. Unable to pull over, I pushed it back in only to completely lose it several minutes later after checking it several times. I was able to replace it with a twin cam dipstick which turns out to be slightly larger. Really had to coax this thing in the hole. Needless to say, it didn't come out on the ride home. However, when I arrived I immediately pulled the plug and am sure that I heard air escaping which leads me to believe that the oil tank is under some pressure. Thanks in advance for any thoughts and advice on this topic.    JoeS

And yes, it was a beautiful mess on a beautiful riding day. 

[2k]

There is a check valve between the tank and motor. If it is not working properly will build undue pressure in the tank. I know I'm not describing this exactly right, but that is the gist of it. Checked my oil one day before a ride, tank way low. Added oil and took off, 3 mi later the cap blew off and coated everything with oil.

[JoeSDE]

Thanks 2k. I think I know what your talking about, a little black plastic piece that clips to the frame in front of the rear wheel.        JoeS

[grc]

The oil pump check valve on Harley's external oil pumps has a history of developing leaks which allow oil from the tank to flow into the sump while not running.  It's a simple ball and seat check valve, accessible from the outside of the pump.  See the attached drawing.  If this happens, and you add oil to the tank before running the engine long enough for the pump to move the oil back to the tank, then as 2k mentioned the tank will become overfilled.  It often also causes excess oil to be blown out the breather system.

Jerry

[JoeSDE]

Usually run the oil a half qt. low and have not added oil this season. The bike has an external breather installed and has never bled oil. Not. Slumping oil as far as I can tell, but the the check valve will get checked as it has never been opened in 16 yrs. Thanks.       JoeS

[HILLSIDECYCLE.COM]

S&S used to offer a tool to re-cut that seat that we've had for years.
Scott

[JoeSDE]

I understand the issue with the check valve in the pump and the associated sumping, but there is no evidence of this happening. Still looking for another reason the oil tank is pressurizing. There are three lines running from the tank to the motor: oil feed line to the pump, return line from the filter and #3, a tank vent line. I have to assume that there is some kind of issue with that line, but have been unable to get an idea of how this line functions. Of course the dealer service dept has no idea of what I'm talking about. Removing the exhaust now to gain access.     JoeS

[JoeSDE]

I've checked the tank vent hose and there seems to be no problem with that. Then I ran the bike for about 5 minutes and pulled the dipstick and found the oil tank to be pressurized. Another mystery of life thanks to Harley. I guess I'll just have to ride it and see if it develops enough pressure to blow the new plug out. Maybe the tank is supposed to have pressure??? Maybe this was a one time event.      JoeS

[grc]

I'm about as far from an expert on Evo's as one can get Joe, so I don't have answers but just questions.  If I remember correctly, a '98 Evo had a head breather system similar to the Twin Cams, with umbrella valves and passages leading to the air cleaner.  The other thing I think I remember correctly is that the oil tank isn't directly vented to atmosphere, but rather to the crankcase or maybe directly to the air cleaner.  What I'm driving at is IF the vent line runs to the crankcase, and the crankcase pressure is excessive, that could be pressurizing your oil tank.  Where exactly does the vent line run on your particular bike?  If it runs to the crankcase, and the line itself is open with no obstructions, you might want to make sure the head breathers are working properly.  If you recently changed air cleaners, check to make sure the breather bolts and backing plate are correct for a head breather bike.  Just throwing out ideas.

Jerry

[JoeSDE]

Thanks for your response Jerry. The vent tube from the oil tank does go to the crankcase, I believe. My heads are vented externally to a crank vent, not back into my air filter. I guess I'll make sure the crankcase is breathing properly by checking the lines from the breather bolts tomorrow. It will be interesting to see if the dipstick blows out when I drive it again.      JoeS

[JoeSDE]

Well, I found the problem. Jerry, as you suspected, the oil tank was being pressurized by way of the crankcase due to improper head breathing. I found that my crank vent was malfunctioning and not allowing the heads to breathe properly. Have no idea why the vent wasn't working because it basically consists of a one way rubber flapper valve. The vent is now technically no longer a one way valve, but I don't think that's a big deal. Ran the bike, no more oil tank pressure, another great learning experience. Thanks again Jerry for keeping me headed in the right direction.     JoeS

[grc]

      Glad you got it sorted out Joe.

Jerry

[Dan_Lockwood]

I've been reading old EVO posts about oil lines/tanks etc and found this one.

My question is this, if the oil pump check valve is leaking and over a month or two of non-running the oil built up in the sump, when started, does the oil get pumped out of the crankcase and back to the oil tank via the crankcase vent just behind and above the pump?

Here is the oil line routing I found.  I hope this is not a double post for me, sorry if it is.

I have an Ultima 113" EVO style motor.  I have the right side gas tank converted to an oil tank and will be running my oil supply, return line and "vent" line all back to the right side tank.  The cap is vented, which it sounds like I may not need.  I may also run a vent line from the tank back down the frame tube to behind the trans and put a vent filter on the end.

My Shovelhead has the same poor design check valve and when it sumps, not running it for a couple months, I blow oil from my crankcase vent out my breather tube at the rear bottom of the frame.  Without head breathers like the EVO/Twin Cam, I think it would be impossible for me to route my vent back to the tank on the Shovelhead.  I just start it once a month with a cookie pan under the bike as a precaution.

Sorry to hijack this thread, but I thought it was probably dead when Joe figured out his problem.

Thanks guys.