REF: Oiling & Lubrication

Wet Sumping

Wet Sumping Due to Extended Storage

  • This is simply oil from the tank draining slowly back down into the crankcase while the bike is parked for any length of time. When you start the engine, the excess oil in the crankcase is fired out the breather, onto the floor, (or into your air-filter on post-79 models). The oil should stop puking after the engine runs a few minutes and pumps the excess oil back up into the tank. Or, you can pull the oil pump off and induce forced air into the crank case to blow the oil out the drain passage from the sump area to the scavenge area of the pump. 1)Some models are equipped with a drain plug under the engine case for this purpose. 2)

Wet Sumping Due to High Revs

  • Wet sumping occurs when the crankcase fills up with oil. The crank has to turn in an oil bath when it's really designed to run in open air. The crank running thru the oil heats it up and adds lots of bubbles. It also really cuts down on the available power.
  • The scavenger pump picks up the oil and sends it to the oil tank. The hotter the oil, and the more air bubbles in the oil, the harder it is for the scavenger pump to move the oil. So, the oil collects in the crankcase even more.
  • The '04 and up Sportsters have had the oil return system redesigned. There are several people having heat and oil consumption issues with 883-1200+ conversions and there are stock bikes having heat and oil consumption issues as well. The 883's and 1200's seem to wet sump worse than years before 2004. Even prior to 2004 Sportster engines were known to wet sump badly under high rpm conditions.
  • The '04 and up bikes are having issues with the return from the heads to the crankcase. The pressure from the crankcase is forced UP thru the passages and the push rod covers to go out the head breathers. This impedes the oil trying to go down. The oil sits in the head longer collecting more heat and getting thinner. Eventually, the oil pools in the head deep enough to cover the valve seals which are not designed to be submerged in oil. The piston sucks the thinned and hot oil thru the valve seal and guide during the intake stroke causing the engine to burn excessive amounts of oil.
  • It is a chain of events that leads to the oil usage symptom. The high heat of the oil also contributes to the problem and that too is caused by the wet sumping. It also will take a bunch of hp on the dyno and on the street as the crank tries to push through solid oil. 3)
    • People have noticed that the '04 and up engines are running much hotter after conversions. Deimus came up with a fix in another thread that may improve the oil flow from the heads to the crankcase. The oil stays cooler, the scavenger pump moves more oil and the problem seems to get better.
    • He basically blocks off the head breathers, and then vents the crankcase thru the cam box with a check valve to the atmosphere. This makes it easier for the oil to move down the oil passages and the push rod covers, and helps the scavenger pump move the oil because on the down stroke, the pistons then aid the oil moving from the crankcase to the cam box. The check valve makes sure that a small vacuum is kept on the cam box which further aides the whole process. 4)

What are the causes, symptoms and affects of wet sumping? 5)

aswracing on rubbermount wetsumping:

  • Sportsters are notorious for having problems with scavenging. Not so much on low rpm steet bikes, but racers have fought this problem for years. 6)
  • It was really bad in the ironhead days, but it was a little easier to deal with, due to the external lines for oiling the top end.
    It was fairly easy to restrict the oil to the top of the motor without restricting oil to the crank.
    With the XR1000 motor (ironhead bottom end) I used to race at Bonneville, I had done several things to make it's oiling system work properly.
    Without those things, the motor would just fill with oil every time we ran it hard.
  • Racers have, for years, lowered oil pressure as a means to reduce oiling system issues.
    Zippers has, for about forever, offered an oiling system bypass kit.
    It bleeds pressure off and sends some of the oil on the pressure side back to the tank, through a special oil tank cap.
  • Ironically, it's always been the motors with the best ring seal that have the worst oiling system issues.
    Gapless rings in Sportster motors are famous for causing wet sumping.
    Remember, the inlet to the scavenge side of the oil pump is in the crankcase.
    So positive crankcase pressure aids scavenging.
    Negative pressure makes the pump's job harder, because the pump is fighting the crankcase vacuum.
    With little to no blow-by and a check valve on the breather system,
  • The crankcase pressure is essentially cycling between atmospheric and negative as the pistons go down and back up.
    (remember, due to the common crankpin 45 degree design, a Harley motor is a variable volume crankcase, unlike most motors)
  • Take a look at a set of S&S cases sometime.
    They have a reed valve isolating the flywheel compartment from the rest of the crankcase.
    The oil pump scavenge inlet is on the other side of that reed valve from the pistons.
    The result is that the inlet to the pump never sees negative crankcase pressure caused by the pistons moving up.
    We have zero, zilch, nada oil system issues with race motors that use S&S cases.
    We can run'em as hard as we want, with whatever rings we want, they never wet sump.

S&S's Engine Solution for Wet Sumping: 7)
Here's the S&S solution to the wet sumping issue.
See the reed valve?
In that compartment under the reed valve, against the far wall, is the oil pump scavenge inlet.
So the pump inlet is isolated from any negative pressure in the flywheel compartment, as the reed valve closes.
This works 100%.

  • In '98, in recognition of the issue, the motor company made a pretty significant change on street bikes.
    The oil pump was given a larger scavenge section, and also an inlet inside the cam box.
    The cam box drain to the crankcase was also blocked off.
    The idea was to put less oil into the crankcase and give more scavenge capacity to the whole system.
    It helped, but high rpm race motors still had the problem.
  • The pump was updated again in '01.
    But it was just a change to the pump body to provide more efficient scavenge operation.
    Issues still happened.
  • Then the rubber mounts came out.
    The very first '04 1250 we ever did, we saw massive wet sumping issues.
    I personally dyno tuned the bike.
    I'd be working the bike, pulling mid to upper 90's for horsepower, getting it hot, and all of a sudden it would fall on it's face.
    I mean, it'd go from 97 hp on one pull to 62 on the next, and you could just tell it was straining.
    Let it cool down for 20 minutes, pull it again, it'd be back in the 90's.
    When a motor wet sumps, the crank is submerged in oil.
    Visualize running a sprint race in knee deep water.
    It kills the power.
    It also contributes to even higher oil temps.
    As circulating oil plays a big part in engine cooling, and with a loss of power, you have to give the bike more throttle to go a given speed.
    More throttle = more fuel burned = more heat.
    It's kind of a viscious circle.
  • And then finally another change was made to the pump in 2007, when they made the scavenge section even bigger and the pressure side smaller.
    Notice a trend here? The focus of every change was to improve scavenging.
  • Later, I built up my '04, and sure enough, same thing happened.
    I'd be dynoing it, getting it good and warm to where it should make it's best numbers, and bam, it'd fall off a cliff.
    Not like that first bike, but I'd still drop more than 10hp from one pull to the next with no changes.
    I have some info on it on one of these old threads around here, I think I even showed the chart.
    But I never revealed what was going on, I figured we'd help customers who ran into it, and let our competitors go figure it out for themselves.
  • To fix it on my bike, I whipped up a simple oiling system bypass.
    It's similar to the Zipper's kit but simpler, to drop the pressure, and the problem disappeared.
    It's been on there so long now I had almost forgotten about it.
    Then Dan started telling me about these issues and had me go running up and down the freeway with him the other day.
  • At one time I was considering whipping up a little oil pressure bypass kit for folks who ran into this issue with their rubber mounts.
    But I shelved the idea due to liability concerns.
    It's really pretty simple though.
    You just tee into the pressure side, between the pump and oil filter, and run it back to the scavenge line and tee it in there.
    Somewhere in that line you put a small jet.
    I think I have a 145 CV jet in mine at the moment.
    With a 165, I would see the oil pressure light flicker on at idle with hot oil. With a 145 it stays off.
  • So why are rubber mounts more susceptible to wet sumping?
    Well, there were a couple of key changes to the oiling system for the rubber mounts.
    • First and foremost, the flywheel compartment of the crankcase vents through the pinion bearing, ala a Twin Cam.
      And yet the scavenge inlet remains in the flywheel compartment, not isolated from the pressure variations of the variable volume crankcase.
    • Second, you've got oil squirters. So you're pumping more oil into the crankcase, and you're getting it hotter.
      Hotter, thinner oil is harder to scavenge and will contribute to wet sumping issues.
    • Finally, the top end drains no longer drain into the crankcase, they turn and dump into the cam box.
      Not sure how this could contribute to the issues but it's a difference, and we sure saw wet sumping issues get a whole lot worse on the rubber mounts.
  • Now, as mentioned, there's also a new pump out, the motor company's latest try at fixing this issue I guess.
    It came out last year on the Buell Ulysess (it fits Sportsters, too).
    Externally it's the same size, but they've increased the size of the scavenge section yet again,
    and reduced the size of the pressure section as well, presumably to lower the pressure. Will it address the issue? I'm not sure.
    I've put one on one of my bikes, but haven't set up the conditions to prove whether it really helps or not.
  • I hadn't heard there's a new pump for the '07 Sportster.
    Is it the same as the Uly pump or something else yet again?
    The Uly pump fits Evo Sportsters as well.
    We need to research that I guess.
  • Is this for sure what's going on? We can't be certain.
    I can tell you for certain that with my '04, with over 100hp, and the oil pressure lowered with a simple bypass kit,
    • I can run that bike as hard as I want and I can't get the oil temp above about 200.
  • So to see others reporting real high oil temperatures,
    and to see Dan's bike running 30 degrees hotter in the same conditions despite having lower compression, well, there's got to be a reason.
  • What we'd like to do is have a few folks who are seeing issues to do something similar on their bikes.
    I'll whip up some pieces, install'em on an engine that I have on my bench right now, and take some pictures.
    It's really pretty simple to do, it's just kind of in a tight spot.
    It can be done without removing the cam box cover though.
    All I had to do on mine was take off the footpeg bracket and I could get in there enough.

The green pull is the very next pull after the red pull, with NO changes to the bike in between those two pulls.
The blue is the same bike a week later, after I had made and installed the little oil pressure bypass kit.|

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