EVO: Oiling & Lubrication

Oil Pump Unit

Sub-Documents

Oil Pump Function

The oil pump is a positive displacement unit.
If you block the discharge flow path, discharge pressure will rise and literally approaches infinity until something fails. 1)
It's non-regulated and delivers its entire volume of oil under pressure to the oil filter mount.
However, don't take the term “positive displacement pump” literally. 2)
Compared to a centrifigal pump, gear / gerotor type pumps use displacement to function.
How positive it is depends on what it's pumping.

The most 'positive' pump on our bikes may be the master cyl for the disc brakes.
You pull the lever and it pumps real good, positive, unless there is air in the system.
Then you still get the displacement but not the pressure because liquid is not compressable but air is.

Gear / gerotor type pumps work by filling the spaces between the teeth with whatever it is that is being pumped (oil in our case).
The oil in the tooth spaces gets squezed out of the spaces when the gear teeth mesh together (because a tooth is now in that space.
But there is still a little space left at full mesh.
Gearotor pumps have a smaller space at full mesh than gear pumps.

Now when the mesh breaks, a void is created. Oil gets sucked into that void.
Now what if air is in the spaces instead of oil?
It gets sqeezed out also unless there is pressure (restriction) in the curcuit its trying to flow into.
In that case, some air stays in the spaces and gets compressed in the small space remaining as the teeth mesh.
When the teeth unmesh, air expands (refilling void that should be getting oil sucked into it.
The pump can't make enough pressure to overcome the exit restriction.
Then there is no flow and no ability to reprime itself since.
(it's not making enough suction due to the expansion of the compressed air refilling the void that the oil should be filling)

Eventually the pressure in the return line gets released.
While this is happening oil is building up in the pickup sump and waiting for the return side to come back online.
The supply pump is still pumping while the return is toggling from air locked to primed and pumping.

Think about what state the return oil is in as it collects in the return pickup cavity. It's just been thru a 60 cycle blender.
Our bikes live with that every mile they travel with lots of air whipped into every drop of return oil.
Restrictions in the return side of the pump will lead to a more sustained oil level in the crankcase sump.
(large enough to reduce outflow from the engine to a volume less than the supply pump is feeding the engine)

This is a condition known as wetsumping.
Read more about wetsumping in the REF section of the Sportsterpedia.

Typical 98-up gerotor positioning over the pickup cavities (07 pump shown). 3)

Oil Pump Pressure

Expected oil pump pressure per FSM's:

Gauge mounted at tappet hole plug

As checked with hot oil and a gauge at the plug hole on the engine case between the tappets.
The plug between the tappets has to be removed for the gauge to be installed.

1986-1990: 4) 5)
Minimum: 1-7 psi (idle)
Normal riding conditions: 5-30 psi (2500 rpm)

1991: 6)
Minimum: 7-12 psi (idle)
Normal riding conditions: 12-17 psi (2500 rpm)

Gauge mounted at oil filter pad

As checked with hot oil and a gauge at the oil pressure switch location at oil filter pad.
The oil pressure switch has to be removed for the gauge to be installed.

1986-1990: 7)
Oil pressure, when checked at the oil filter pad (oil pressure switch removed), will be 6-10 psi higher than when checked at the tappet plug on the case at idle.
See pressure figures above when checked at the tappet plug hole.

1992-2004: 8) 9) 10) 11) 12) 13) 14)
Minimum: 7-12 psi (idle speed varies from 950-1050 rpm between the different FSMs)
Normal riding conditions: 10-17 psi (2500 rpm)

2013 XR1200X: 15)
Minimum: 16-20 psi (idle)
Normal riding conditions: 40-44 psi (2500 rpm)
Oil pressure relief (50 psi)

  • It includes an oil cooler with a thermostat that starts to open at 190ºF (88ºC).
  • The oil pump and the head breathers are a new design.
    The oil pump rotors are driven by the cams, the feed rotor is driven off the front intake cam and the scavenge rotor is driven by the rear exhaust cam.


Oil Pump - Complete Unit Part Numbers

1986-1990 Models - XL P/N = 26204-86
- pump body catalog p/n 26484-86
- pump body casting p/n 26485-
… casting p/n is in return cavity
… also has a “2” stamped next to casting #
… also has a “T” stamped into opposite return cavity
- bottom cover catalog p/n 26486-86
- bottom cover casting p/n 26487-86

1991-1996 Models - XL P/N = 26204-91
- pump body casting p/n in 26485-90
… casting p/n is in the return cavity
… also has casting #s 1 and 380 in opposite return cavity
- pump cover casting p/n 26487-90
… casting p/n is on the outside of the cover

1997 Models - XL P/N = 26204-91
- pump body casting p/n in 26485-90A
… casting p/n is in the return cavity
- pump cover casting p/n 26487-90A
… casting p/n is on the outside of the cover

1998-1999 Models - XL P/N = 26204-98
- From the internal P/N changes it appears that this new
… P/N was generated because of a change in the
… Gear Shaft and Gerotor Return set of gears
- has body casting P/N 26487-98 in the return cavity
- has bottom cover casting P/N 26487-98 on the outside

2000-2006 Models - XL P/N = 26204-91A
- P/N change appears to be related to a fitting (to oil filter) change
- has bottom cover casting P/N 26487-98

2007-later Models - XL P/N = 26204-91A (new design)
- is a different design w/same P/N (How crazy is that?)
- is retrofitable to 1991-2006
- has body casting P/N 26211-07 in the return cavity
- has bottom cover casting P/N 26213-07
on the outside

Buell P/N - 26357-02B
- same pump as XL 26204-91A (new design) but different fittings
- will bolt up but you need to change the fittings over to XL style
- has bottom cover casting P/N 26213-07

See these XLForum threads:
http://xlforum.net/forums/showthread.php?t=135265
http://xlforum.net/forums/showthread.php?t=1738158


Oil Pump Date Code

91 and Up Oil Pumps

The casting date code is in a circle on the mounting surface near the return fitting.
A 'year of manufacture' number is stamped inside the circle with 12 hash marks around the circle.
Dots are cast around the hash marks to represent the month of manufacture.
Count the dots, add the year and you have the month and year of manufacture for that particular oil pump.

91-96 Pump assembly 26204-91 16) 97 Pump assembly 26204-91 17)
98-03 Pump assembly 26204-98 18) 07-Up Pump assembly 26204-91A 19)

Oil Pump Upgrade 26204-91A

  • In addition to the upgraded Drive Gear (26391-06), there is also an upgraded entire Oil Pump (first installed on 07-later Sportsters). The new pump reuses the same full unit part number as a previous version, making it difficult & confusing to know to which version someone is referring. The old (& new) part number for the complete oil pump unit is 26204-91A (that P/N first showed up in model year 2000 and used for the older design thru model year 2006).
  • The difference between the 1998-2006 version and the 2007-later version relates to the drive shaft, internal Gerotor return & feed gears and the body (which cannot be ordered separately). The internal parts for the new pump design are not backward compatible to the 98-06 pump design.
  • The only known external indicator to identify that the 2007 pump version (using P/N 26204-91A) is currently installed is the cover casting number 26213-07 which is stamped on the bottom of the new version.
  • The upgraded pump is compatible (and recommended) for use on 1991-later Sportsters.

Here are the internal servicing part numbers from 1998-2000 version and 2007-later version:

Part Name 1998 P/N 2007 P/N
Gear Shaft 26488-98 26239-07
Gerotor Return Set 26491-98 26502-07
Gerotor Feed Set 26492-91 26503-07
Separator Plate 26493-91 Unknown?
Bottom Gasket 26495-89A 26495-89B


26204-91a-2007-oilpumpkit.jpg 20)


2007 XL and Buell Oil Pump Comparison

  • 2007 XB engines got a new up-dated oil pump which will retro fit to older EVO Sportster Engines, BLAST engines and older XB Engines … 21)
  • The -07 XB oil pump is part number 26357-02b. The 07 part number seen on the housing is simply just for the lower housing. 22)
  • The part number for a 2006 is 26357-02A. 23)
  • The -07 Sportster pump changed at the same time and got the same improvements and the only reason the part number is different from the Buell pump is that the fittings are different. And what's more, just a brief look at some parts books shows that the part number for all Sportster pumps from 2000 to thru 2007 + is the same (26204-91A). So they changed the pump in 2007 as Buell did. However, it doesn't appear that they changed the part number. So with the 07-up XL style oil pump, even though the pump’s part number didn’t change from the 2000 model year, the gerotor part numbers did.
  • Both the Sportster 2007 Oil Pump (26204-91A) and Buell 2007 Oil Pump (26357-02B) have gerotors with the following same part numbers:
    • Feed — 26503-07 GEROTOR SET
    • Return - 26502-07 GEROTOR SET
  • So, it does appear that the Sportster got the same oil pump improvements. Why they changed the Buell pump part number in '07, and yet didn't change the Sportster pump part number at the same time, I have no idea. Just to confuse us I guess. 24)
  • The Sportster pump #26204-91A and the Buell pump # 26357-02B are the same 25)
  • The only difference in the pumps are the fittings that come installed on the pump 26) which can be removed and replaced with the fittings that you need for your XL.

Oil Pump Drive Gear

88 and up:
Below is a used gear that does show some wear.
27) 28)

Dims are also from this used gear. 29)

Sub-Documents

Gear Configuration

The gear mesh (oil pump driveshaft gear to drive gear on the pinion shaft) looks to be a worm gear configuration.
However, that is not accurate. It's actually two right handed helical gears in a 90 degree configuration (or cross axis helical gears).

The teeth on these gears stay in contact longer than straight teeth spur gears. 30)
(which allows them to transmit higher loads at higher speeds than spur gears)
The gears are carbon steel for strength with hardened teeth for increased wear resistance.
(once axial play wears the hardness, the teeth wear down rather quickly)

For the gears to mesh correctly, they must have the same pressure angle and pitch.
Helical gears can be configured to transmit motion in a straight line (or used for Sporty oil pumps at a 90° angle).
To transmit motion at a 90° angle, 2 gears are paired in the same tooth direction (right handed).

Oil Pump RPM

There are 10 teeth on the drive gear at the pinion shaft and 20 teeth on the oil pump driveshaft.
This creates a 2:1 ratio of the gears (20/10 = 2:1) meaning the oil pump RPM is half the speed of the engine.
(running at 4,000 RPM, the oil pump is turning at 2,000 RPM)

Drive Gear Removal

The drive gear is inside the gearcase and the cover will need to be removed to access the gear.
See Removing the cam cover in the Sportsterpedia.
With the cover off, you'll need a tool to lock the pinion gear to remove the nut that holds the assembly together.
Once the pinion gear is removed, the pump drive gear slides off the pinion shaft.

Known Drive Gear Failure

Inspect your oil pump drive gear especially if you've gotten your gearcase cover off anyway to hopefully prevent gear failure before it happens.

  • This is a common failure in Sportsters, even when nothing gets into the pump to lock it up first. 31) The teeth get sharp and then they break off.
    If something gets into the pump and locks it up, the teeth get ripped off the gear. 32)
  • The failure happens because of pinion shaft runout which causes the engagement depth of the teeth to change as the pinion shaft rotates.
    What happens is the gear will wear badly in one area. You'll see the teeth getting real sharp there. 180 degrees from that spot, the gear will look like new. 33)
  • So lots of people get fooled when they check the gear. They'll look at the visible portion from their vantage point only.
    You have to look all the way around the gear though. The wear will be isolated to one area only. 34)
  • With the gearcase on, you may be able to pull the oil pump and look up inside, and inspect the gear while slowly turning the motor. 35)
  • With the gearcase on, you may still want to remove the pinion nut and gear to get a good prospective on the health of the drive gear.
    The damage can be easily overlooked.
    It usually happens on one side of the teeth on the gear due to pinion shaft runout forcing the gear outward while it is moving against the rigid mounted oil pump gear.
    Read more about it in the upgrade article.
Teeth worn thin on the stock oil pump gear. 36) Comparison with a new bronze gear. 37)
  • Concerns of the carnage if the gear shrapnels:
    • Debris locking up the oil pump.
    • Scoring the oil pump cylinder, feed and scavenge gears which opens up the tolerances keeping it from pumping oil correctly in the future.
    • The debris is also exposed to (everywhere oils travels) as in all the inboard cam bushings 38), rings, cylinders, rockers etc. so it can be catastrophic failure depending on the severity of the initial damage.
  • Cleanup upon discovering broken / exploded metal parts anywhere in the engine:
    • Simple answer, check and clean everywhere oil can travel. Choosing not to has proven to be destructive to the engine.
    • You can run a magnet along most non-confined areas to check and remove metal particles.
Oil pump and drive gear damage. 39)
More oil pump and drive gear damage 40)

 A chunk of a tooth from the oil pump gear fell out of the oil pump upon dis-assembly 41)

Priming the Oil Pump

A dry pump won't pump oil.
It will 'cavitate' when their is not a hydraulic seal between the gerotors and the inlet hose from the tank.

Any time you have removed the oil pump or the removed / drained the feed hose from the oil tank, the pump needs to be primed.

  • The oil pump needs to be primed with oil / lube before it can transfer oil from the inlet to the outlet cavity inside.
    • Prime the oil pump per the FSM;
      • Upon removal / inspection, oil the pump internals.
      • Remove the oil pressure switch and rotate the engine until oil comes out the end of the pump and reinstall the switch.
    • If you let it sit long enough, oil will gravity drain inside the pump and prime it.
    • Another way to prime the pump is to use assembly lube on the gerotors and inside of the pump before installing it. 42)
      Then you have an instant hydraulic seal to help the oil pump suck oil from the hose.
    • You can also using a large syringe with a tapered tip inserted into the oil supply hose on the bottom of the oil tank. 43)
      Then you can force feed oil the pump and on to the engine using this technique and it avoids having to mess with the sending unit.


3) , 16) , 17) , 29)
photos by Hippysmack
4)
1986 HD FSM pgs 3-2
5)
1986-1990 HD FSM pgs 3-2, 3-10
6)
1991 HD FSM pgs 3-2, 3-32
7)
1986-1990 HD FSM pg 3-10
8)
1991-1992 HD Sportster FSM pgs 3-2, 3-32
9)
1993-1994 HD Sportster FSM pgs 3-3, 3-40
10)
1995-1996 HD Sportster FSM pgs 3-3, 3-38
11)
1998 HD Sportster FSM pgs 3-3, 3-38
12)
1999 HD Sportster FSM pgs 3-3, 3-40
13)
2000 HD Sportster FSM pgs 3-3, 3-6, 3-54
14)
2004 HD Sportster FSM pgs 3-3, 3-14
15)
shanneba from the XLFORUM- 2013 Factory Service Manual
18) , 19) , 27) , 36) , 37)
photo by Hippysmack
28)
drawing by Hippysmack
39)
photo by xtremer-pxl of the XLFORUM http://xlforum.net/forums/showthread.php?t=1848987
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