See also Installing an Oil Pressure Gauge in the Sportsterpedia.

All Sportsters have oil pressure, even ironheads.
It's also been said that putting an oil gauge on an ironhead is useless due to the low oil pressure they operate on.

However, most Sportsters operate off low oil pressure especially during hot idle.
The pressure source is shared between the oil pump and crankcase pressure from the action underneath the pistons.

The first answer is to rely on the oil light.
However, an oil gauge can be fitted to any Sportster.

See also in the Sportsterpedia:
Ironhead Oil Pumps
Evo Oil Pumps

• All Sportster oil pumps are unregulated during operation and will deliver their entire volume of oil under pressure to the engine or oil filter mount (respectively).
• The oil pump is geared to the pinion shaft and operates faster (increasing oil pressure) or slower (decreasing oil pressure) depending on the revs used.
  
• Oil viscosity will affect oil pressure.
  • On a cold startup, the oil's viscosity is thicker and this will result in a higher oil pressure but circulation will be restricted somewhat.
  • As the engine warms up, oil gets hot and thinner resulting in higher circulation and a decrease in oil pressure.
• Oil pressure readings are generally taken at the oil pressure switch outlet (oil pressure switch removed).
  • However, the pressure figures for 86-91 models (listed in the FSMs) are based on testing from the tappet hole plug on the engine case between the tappets.
    (although, a gauge can be installed at the pressure switch or the oil pump with the proper fittings)
• Installing a gauge on the rocker boxes will not do a lot of good for comparison or useable results.
  • The oil source is transferred from hydraulic (oil pump) to gravity and slung force (piston down-force) by the time it gets to the rockers.
• An adapter can be added at the oil pump housing to split the piping to the oil pressure switch or filter pad (respectively)and the oil pressure gauge.
• Run the engine to normal operating temperature and check the gauge.
• Check your readings against the expected oil pump pressures below or your FSM.

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. ¹⁾
    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. ²⁾
    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.

Expected oil pump pressure per FSM's:

As checked with hot oil and a gauge at the oil pressure switch location at the oil pump.
The oil pressure switch has to be removed for the gauge to be installed.
Oil filter is on the return side of the oil pump giving less restriction to the feed side.

1957-1969: ³⁾
Minimum: 3-7 psi (idle, with spark retarded)
Normal riding conditions: 10-14 psi (6 psi at 20 mph)

1970-1978: ⁴⁾
Minimum: 3-7 psi (idle)
Maximum: 15 psi (60 mph in high gear)
Normal riding conditions: 4-15 psi

1979-1985: ⁵⁾
Minimum: 4-7 psi (idle)
Maximum: 10-20 psi (3500 rpm)
Normal riding conditions: 4-15 psi

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.
Oil filter is on the feed side of the pump giving more restriction on the feed side.

1986-1990: ^{6) 7)}
Minimum: 1-7 psi (idle)
Normal riding conditions: 5-30 psi (2500 rpm)

1991: ⁸⁾
Minimum: 7-12 psi (idle)
Normal riding conditions: 12-17 psi (2500 rpm)

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: ⁹⁾
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: ^{10) 11) 12) 13) 14) 15) 16)}
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: ¹⁷⁾
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.

Installing a gauge at the rocker box is basically useless in diagnosing from the FSM.
There are no specs in the manuals to support any readings taken from the rockers.
However, below are some noted pressure readings from XLFORUM members.

A 0-15 psi gauge (although it will max out with a cold motor) will give you the most accurate readings with hot oil. ¹⁸⁾
A 0-30 psi gauge is only useful at cold temps.
A 0-60 psi gauge is useless when testing from the rocker box.
All of this depends on the oil you are running also.

Multiple viscosity oils will show low to no pressure at running hot or cold idle.
50 wt in the summer shows lower pressure while 60 wt.

• 3-5 psi at hot idle.
• 15 psi+ when cold.
• 7-10 psi during normal riding conditions.

Other XLF member results noted from the rocker box:

• Cold start, running 20/50, - pressure off the scale at startup. ¹⁹⁾
  • Settled to 8-9 psi after a few minutes at fast idle.
  • After 2 miles, the pressure was steady at 12 psi.
  • After 5 miles, pressure dropped to 1-2 psi.
  • After 11 miles, pressure dropped to zero and stayed there.
  • When stopped at end of ride, it stayed at zero on idle.
  • Will see if the same thing happens at the weekend.

Click here to view the Oil Pump Pressure page in the Sportsterpedia.