REF: Oiling & Lubrication

Wet Sumping

See also in the REF section of the Sportsterpedia:

Wet sumping is a condition between the flywheels and the scavenge passage.
Oil collects in the bottom (sump) area the crankshaft when the oil is not scavenged out fast enough (or during extended shutdown periods)
When the oil balance between feed and scavenge is correct, there should be very little oil gathering in the sump during operation.
However, the sump should not be dry during operation.
A dry sump system simply means the oil supply is not stored in the crankcase as does V-8's.
Instead, the oil supply is stored in the external tank.
During wet sumping, sump oil is churned by the flywheels, air attaches to it leaving (not all but) some of it in the sump longer.
Oil drags the wheels, heat rises and this affects crankcase pressure balance.
It also adds more drag on engine parts to increase engine wear.

How sumped oil plays into engine breathing is it allows more oil in the sump to be picked up and slung out the breather vent. If there wasn't much oil in the sump and the breather vent fails, you get less oil out the A/C even though engine breathing was compromised. It's a balance. But even then, normal splash oil would be seen out the breather.

It can be attributed to inhibiting crank rotation until the excess oil is returned to the oil tank by the scavenge side of the oil pump.
In extreme cases, it can also be attributed to engine wear, i.e. racing applications.
This can and most likely will happen at one point or another in stock as well as performance engines.
Acceleration is hampered until the oil clears the crank area.

Known causes of wet sumping during engine down time:
This is simply oil from the tank draining slowly back down into the crankcase while the bike is parked for any length of time. 1)
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).

  • Oil Pump:
    • Worn / damaged oil pump scavenge gears or gerotors (respectively).
      The oil pump can't return as much oil to the oil tank as it is receiving from the feed side of the pump.
    • Damaged teeth or broken gear keys can stop the movement of the teeth thus stopping the scavenge side from working.
      It's entirely possible for the feed side to work with the scavenge side not working.
      (but that won't last long without something detrimental happening)
    • Worn / damaged seals (or plates respectively) between the scavenge and feed side of the oil pump.
      Gravity pressure is always present on the feed side of the pump.
      If the seal between the feed and scavenge side is compromised, that gravity oil will seep past the scavenge side and into the engine.
  • Check Ball / Check Valve:
    All Sportsters have some sort of an oil check system in place.
    The check ball can be thought of as the on / off valve for oil supply into the engine.
    On 57-85 engines, the check is in the oil pump and on 86 and up engines, the check is in the oil filter pad.
    The main objective of the oil check is to close the oil passage during engine shutdown to stop a wet sump condition.
    Occasionally the check gets weak or damaged and allows oil to bypass it during shut down.
    This will cause wet sumping.
    • The 57-76 check ball seat in the oil pump body can get dirty and / or pitted from usage and debris.
    • The spring (whether check ball or valve) can break or weaken which won't push the unit against the seat properly.
      Without adequate seat pressure, oil will bypass into the engine.

The check valve is spring loaded. Debris can lodge in the spring seat and keep it open.
The spring can also get weak with wear and the cup seat may not sit properly to seal off.

77-E87 check valve 2)Check valve in 77-85 oil pump 3)Check valve in 86-E87 filter pad 4)

A small particle of debris may be lodged at the seat position of the check ball keeping the passage open.
The check ball may have rings formed on it at the seat position by the seating action itself over time.
If the ball doesn't fall back on the ringed area every time the engine shuts down, oil will leak into the groove and then the engine.
A check ball that is no longer perfectly round will not sit properly on the round seat and oil will leak past it into the engine.

Known causes of wet sumping during engine operation:

  • Oil Line(s):
    • An oil may be pinched / collapsed, or stopped up.
      A blockage in the return line will not allow the scavenge pump to remove the oil from the sump or move it out fast enough to keep up with feed oil from the pump.
    • On ironhead engines with the oil filter in the return line, a stopped up oil filter can hinder adequate oil flow out of the engine.
    • A blockage in the vent line from the oil tank to the cam chest can prevent proper oil return pressure from going to the oil tank.
  • 86-91 engine oil pressure regulator:
    • The discharge from the relief valve drains down into the gearcase.
      Then that 'extra' oil and is routed to the crankcase sump through a hole in the case wall and gets pumped back to the tank.
      The 'extra' oil adds volume to the sump, thus adds towards a wet sumping condition.
      A weak spring or a bad seat at the plunger will cause the regulator to open more often and / or unnecessarily increasing the possibility of wet sumping while riding.
1986-90 Oil Filter Mount 5)

Is your Engine Wet Sumping?

Common red flags include:

Oil puking out the breather(s):

  • Oil puking out of the breather tube (pre 91 engines) or the air cleaner (post 91 engines).
  • Over extended storage periods (winter or down for repairs), oil from the tank drains slowly down into the crankcase.
    When you start the engine, the excess oil in the crankcase can be fired out the breather vent(s) and onto the bike / floor.
    See also Evo Crankcase Pressure and Engine Breathing

Lower oil level in the oil tank over various periods of down time.
See also Overfilling the Oil Tank

  • The amount of oil (when parked) was correct.
    Upon later inspection, the tank may be 1-2 quarts low on the stick.
    NEVER check the oil level without first running the engine up to operating temp.
    This allows the oil pump to return most of the oil in the sump back to the oil tank before checking the level.
  • Overfilling the oil tank can increase wet sumping:
    • If you fill the tank (improperly), this will result in too much oil in the engine.
      It can also result in oil blowing out the oil tank cap or breather(s).

Lower oil level in the tank after a hard ride.
A good way to tell if your engine is wet sumping (during a hard ride) is to check the oil level right after a leisurely ride. 6)
Then go out and thrash the Hell out of the bike, immediately shut the bike off and check the oil level again.
If it is a lot lower, then it is wet sumping.

A sudden loss of power while riding.
See Wet Sumping Due to High Revs below.

  • After some spirited riding and high RPM passing of cages, particularly riding 2up, the power is just not where it should be. 7)
    The bike will continue to accelerate, but not at it's normal rate.

Difficulty turning the engine over when it's hot. 8)

  • Just think about trying to push a piston downwards through a pool of oil.

Clearing the Sump of Excess Oil

Related articles in the Sportsterpedia:
………* Performing a Scavenging Oil Change
………* Sportster Drain Plugs Explained

  • The oil should stop puking after the engine runs a few minutes and pumps the excess oil back up into the tank.
  • (57-76 models only) are equipped with a sump drain plug under the engine case.
    This plug (near the seam between the cases) is known for stripped threads or cracks in the case around the plug once removed.
  • 77 and up models do not have a dedicated sump drain.
    There is a drain plug under the engine but it is a rifling hole to connect the sump scavenge hole to the oil pump scavenge galley.
    Removing this plug will most likely drain some oil but it will not empty the sump of oil.
    The oil runs uphill from the sump area to the oil pump so the elevation doesn't match up to gravity drain the entire sump.

Wet Sumping Due to High Revs

See also Engine and Primary Oil System Modifications in the REF section of the Sportsterpedia.

  • 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 symptoms are sudden dwindling of power and the oil fogging out of the (breather) vent. 9)
    Simply slowing the rpm can make it quit very quickly.
    When shut off immediately during wet sumping, you may check the oil dipstick to find the oil level low or almost dry.
    Fire it back up and it should fill the tank almost full again.
  • When sumping, it may feek like the motor sort of seized up. 10)
    When it happens you know it!
    Very sluggish, won't pull and higher oil temp.
  • 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. 11)
    • 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. 12)

What are the causes, symptoms and affects of wet sumping? 13)

aswracing on rubbermount wet sumping at high revs:

  • Sportsters are notorious for having problems with scavenging. Not so much on low rpm steet bikes, but racers have fought this problem for years. 14)
  • 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: 15)
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%.

16)
  • 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.
    ( link to the article with pics in the Sportsterpedia here: 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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