IH: Oiling & Lubrication

Engine Oiling

Oil Tank Pressure

See the full article, Oil Tank Pressure, in the REF section of the Sportsterpedia.
There should not be any noticeable pressure in the oil tank.

During normal operation;
With the tank cap / dipstick removed, tank pressure is vented to atmosphere from the top of the tank.
With the tank cap / dipstick installed, tank pressure is vented to the cam chest.

During shutdown;
The oil tank vent is connected to the cam chest and the cam chest is vented out the breather valve in the cam cover.
So if you have pressure in your oil tank and the vent to the cam chest is not blocked then the cam chest is also pressurized.
If the cam chest is holding pressure, then your breather valve can not be venting properly.

Bottom line is that if the vent system is working properly, you shouldn't have excessive pressure build up in the oil tank. 1)

Changing / Draining Engine Oil

Oil Tank Capacity

1970-19783 quarts
1979-19814 quarts
1982-19853 quarts

Oil Filter

1970-E1980Drop in element (63840)

Oil Filter Mount

See also Remote Oil Filters in the REF section of the Sportsterpedia.

—– 1957-1979 XL - XLH Models —–

XLCH models did not have an oil filter.
XL / XLH models have an oil filter mounted inside the oil tank.

76 XLH filter in tank. 2) 'Drop in' oil filter. 3)

1979 models didn't come with an external filter as a base sale from the MoCo.
The oil filter was mounted in the oil tank as in previous years. However, an oil filter kit was debuted in 79 as an accessory item.
So some may have them and others may have the filter inside the oil tank.

—– 1980-1981 Models —–

The oil filter was relocated on 1980 and up models and they were fitted with an external oil filter.
The filter mount is located on a bracket between the engine and the oil tank.
It's under the seat in a awkward place to work with. 4)

Wide angle of filter location 5)
Oil filter mount on 81 model. 6)
The hooked hose fitting is connected to the oil return hose from the pump. The straight hose fitting in the middle goes to the oil tank. 7)

—– 1982-E1984 Models —–

The filter mount is mounted on the lower left front engine mount.
This has also been a popular practice on earlier bikes.

82-E84 motor / filter mount. 8)Filter installed on an 80 XLH motor mount. 9)83 model. 10)

—– L1984-1985 Models —–

The oil filter on alternator ironheads is where the generator used to be. 11)
Two fittings (feed and return) are on the right case below the filter.
Room was made there due to the new alternator location.
This change was made along with the breather baffle tube assembly installed in the cam cover.
The oil slinger system was eliminated.

Oil Filter Adapter (L84-85)

The threads on each end of the oil filter adapter are the same.
The I.D. on each end is also the same.
The adapter can be installed from either side as there is no check valve / check ball involved with the oil filter mount.

Thread the adapter into the filter pad. No thread dressing is suggested by the FSM.
However, a light coat of anti-seize would protect the threads upon later removal of the adapter (if necessary).
Torque: 8-12 ft/lbs. 12)


Engine Oil Cycle (1976 and Earlier)

  • Oil is gravity fed from the oil tank to the oil pump. 13)
    • A check valve in the oil pump prevents the oil from draining into the engine by gravity.
  • Then, the oil pump supplies pressurized oil into a hole in the cam cover.
    • That pressurized oil is forced up the lines (between the cylinders) to the rocker box by the oil pump.
    • That is the vertical end of responsibility (pressure wise) for the oil pump.
  • In the rocker boxes, oil gathers and splashes over rocker arm bearings and rods, valve stems, valve springs and pushrod sockets.
  • Before the oil reaches the rocker lines, it splits off to a hole through the pinion shaft (to get to the rod bearings).
    • This is the horizontal end of responsibility (pressure wise) for the oil pump.
  • From here on, oil travels through the engine by way of gravity, vacuum and splash motion.
    • Oil drains from the heads through passages in each cylinder.
      • Then it flows into two holes in the base of each cylinder while lubricating the cylinder walls, pistons, rings and main bearings.14)
    • Oil flows from the rocker boxes into the gearcase compartment through the pushrod tubes.
      • Parts lubricated by this include the pushrods, tappets, tappet guides and tappet rollers and cam gears.
    • Oil accumulated in the crankcase base is scavenged by the flywheels to the breather oil trap.
      The rotary breather valve is timed to open on the downward stroke of the pistons.
      This allows crankcase exhaust air pressure to expel scavenge oil from the crankcase breather oil trap into the gearcase.
      The breather valve closes on upward stroke of the pistons, creating vacuum in the crankcase.
  • This splash oil blown from the crankcase to the gearcase lubricates the generator drive gear, cam gears and cam bearings.
  • Crankcase exhaust air escapes from the timing gearcase through the outside breather tube.15) Any oil still carried by exhaust air is separated form the air by an oil slinger on the generator drive gear.16)
  • Gearcase oil flows through the fine mesh oil strainer preventing foreign particles from entering the scavenge section of the oil pump.17)
  • Engine oil returns to the oil tank by the scavenge side of the oil pump and also supplies oil to the rear chain oiler 18)

Engine Oil Cycle (1977 to 1985)

  • Oil is gravity fed to the gerotor type oil pump. Oil enters the feed section and fills a cavity under the feed pump. Oil is transferred from the inlet cavity to a one way check valve located in the outlet line. 19)
  • The check valve prevents gravity oil drainage from the oil tank to the engine and acts as a restriction to activate the pressure switch. The check valve is set to open between 4 psi and 6 psi of oil pressure. 20)
  • As the oil pump pressurizes, it causes the oil pressure indicator light, sending unit to activate and the check valve opens. With the check valve open, oil flows into the right case half through a hole located in the oil pump gasket surface and into the gearcase cover passage through a hole in the gearcase cover gasket. 21)
  • Oil is routed to the crankshaft and to the head areas. Oil enters a hole in the pinion gear shaft and travels to the right flywheel then through the flywheel to the crank pin. Oil is forced out of the crank pin through 3 holes located to properly lubricate the rod bearing assembly. 22)
  • Oil that bypasses the pinion gear shaft travels upward through the gearcase cover to the right crankcase and through a channel in the crankcase to the overhead lines to both front and rear intake rocker arm shafts, lubricating the rocker arm shafts, bushings, intake valves and pushrods. 23)
  • Oil continues around a groove machined in the outside diameter of the large end of the rocker arm shaft and through the rocker arm arm cover to the exhaust rocker arm shaft lubricating the rocker arm bushings, valves and pushrods in the same manner as is described for the intake shafts. 24)
  • Oil collected in the pushrod area of the heads flows down the pushrod covers to lubricate the lifters. The lifter's rollers are lubricated by oil draining into the gearcase through the 2 drain holes in the lifter bodies. 25)
  • Oil collected in the valve spring pockets drains to the flywheel compartment through horizontal holes in the cylinders. Oil returning from the heads, rod assembly and gearcase collects in the sump area below the flywheels. 26)
  • Oil collected in the sump area returns to the scavenger section of the oil pump through a passage located in the rear section of the pump. Oil flow to the pump is accomplished by the scavenger effect of the oil pump and the pressure created from the downward stroke of the pistons. 27)
  • Return oil fills a cavity above the scavenger section of the pump which transfers return oil to the outlet side of the pump and sends the oil back to the oil tank.
  • All engine breathing is accomplished through the gearcase into the breather system. Any oil still carried by the exhaust air is centrifugally separated from the air by an oil slinger on the end of the generator drive gear shaft.28)
  • Crankcase exhaust air is routed through a one way check valve to the air cleaner. 29)

Engine Oil Pressure (57-85)

See also Sportster Oil Pressure (57 to Present) in the REF section of the Sportsterpedia.

The oil pump is non-regulatory and delivers its entire volume of oil under pressure to the oil filter mount.
When an engine is cold, the engine oil will be more viscous (ie., thicker).
During start-up of a cold engine, oil pressure will be higher than normal and oil circulation will be somewhat restricted within the oiling system.
As the engine wams to normal operating temperature, the engine oil will warm up also and become less viscous - oil pressure will decrease.

When an engine is operated at high speeds;
The volume of oil circulated through the oiling system increases, resulting in higher oil pressure.
As engine speed is reduced, the volume of oil pumped is also reduced, resulting in lower oil pressure.

Ironhead engine oil pressure was measured (by the MoCo) with a pressure gauge at the oil pump.
See expected oil pump pressures below (per FSM's):

Gauge mounted at oil pump:

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.

1957-1969: 30)
Minimum: 3-7 psi (idle, with spark retarded)
Normal riding conditions: 10-14 psi (6 psi at 20 mph)

1970-1978: 31)
Minimum: 3-7 psi (idle)
Maximum: 15 psi (60 mph in high gear)
Normal riding conditions: 4-15 psi

1979-1985: 32)
Minimum: 4-7 psi (idle)
Maximum: 10-20 psi (3500 rpm)
Normal riding conditions: 4-15 psi

Note: On a cold startup, expect pressure to reach ~60 psi 33)

Checking Oil Pressure

See also Installing an Oil Pressure Gauge in the Sportsterpedia.

When checking oil pressure, it's important to note that you are not testing pressure at a dead stop standpoint.
The oil is flowing into the engine at the same time you are testing from a still test site.
Likewise, the resulting pressure reading is a reflection of residual pressure while that pressure is being manipulated.
(by oil flow as well as the current viscosity)

According to the MoCo (FSMs), the oil pump is the prime testing point of oil pressure to the engine.
The procedure is to take the oil pressure gauge off and install an oil gauge there.
This works if you have verified that you do have oil flow to the engine and just want to check the pressure at the pump.
This takes the oil pressure switch as well as the oil light out of line.

However a tee can be added inline for a dedicated gauge.
You can either mount a permanent gauge to the tap or plug it off until needed.
This will keep the switch and the oil light inline and working if you need it.

34) 35)

Low Oil Pressure

The oil pressure light can fluctuate on and off for many reasons.
It doesn't necessarily mean you have low oil pressure (or flow) to the engine.

However, it does warrant immediate concern and diagnosis.
In fact, at idle, the oil pump check valve is barely opened past it's cracking pressure.
Low revs at idle can cause the oil light to flicker off and on.

First, verify that the oil pressure light is functioning properly:

  • Check for a loose or faulty connection at the oil pressure switch.
    • The wire connection at the oil pressure switch has to be tight so vibration won't cause intermittent signal loss to the oil light.
  • Inspect the signal wire between the light and the pressure switch for kinks, cuts or faults.
    • Make sure it's not grounding out on nearby metal parts (especially melted PVC jackets under wire ties).
    • Run a continuity test on the entire length of wire with a multi-meter.
    • Repair or replace the wire as needed.
  • Verify the light is not faulty or burnt out.
    • Disconnect the wire at the oil pressure switch.
    • Run a jumper wire off the (+) side of the battery to the end of the oil light wire.
    • Verify it lights up and then bump the light by hand to verify vibration doesn't affect it.

Verify the oil pressure switch is working properly:

  • The oil pressure switch is a spring loaded diaphragm.
    • With insufficient pressure pushing against the spring mechanism, the switch is normally grounded.
    • This grounds out the circuit to the light, and it stays unlit.
  • With adequate oil pressure against the spring, the ground contact is broken which lights up the oil light.
  • If the pressure switch is stuck in the closed position;
    • The circuit stays grounded and the light will not come on.
  • If the pressure switch is stuck in the open position;
    • The light will come on during startup and stay on during engine operation.
  • If the pressure spring is changed with a stiffer spring (57-76);
    • The oil pump will not make sufficient pressure to overcome the spring pressure at warm idle.
    • The oil light will illuminate on a cold startup due to startup oil pressure.
    • The light will then go out when the oil heats up (lowered pressure against the spring).

A faulty oil pump check valve will not turn off the oil light:
The restricted orifice in the check valve creates the back pressure to actuate the oil pressure switch.

  • If the check valve is stuck in the open position;
    • The oil still has to travel through the restricted orifice in the check which creates backpressure to actuate the pressure switch → oil light.
  • If the check valve was stuck in the closed position;
    • Pressure would still build up inside the oil pump and actuate the oil pressure switch and then the oil light.
    • This would seem like everything is fine with the engine running and the light off.
    • However, with the check closed, no oil would enter the engine.

Check for possible causes of low oil pressure:

  • If the tank is empty, obviously oil pressure will be low.
    Check for oil returning to the oil tank.
  • The oil filter (if applicable) could be restricted or plugged up.
  • The oil lines may be pinched / collapsed, leaking or stopped up.
    Inspect the oil lines.
  • There has been occasions where silicon (placed on the oil pump gasket during installation) had made it's way into orifices inside the engine.
    You can blow compressed air thru oil inlet and outlets in the engine.
    You can also blow out the oil lines.
  • The oil check valve could be stuck closed.
  • No oil to the top end:
    • Make sure the rubber grommets on each end of the stock rocker feed lines are not partially plugging the ends of the rocker feed lines.
      Then remove the allen-hex rocker spindle plug from the front exhaust rocker spindle, at the right-hand side of the rocker box.
      Oil should come out there if you have flow with the engine running. 36)
    • You can loosen or remove the 1/8“ NPT pipe plug from the right side, front corner of each rocker cover.
      With the engine at idle, you should get a small amount of oil plopping out (not shooting out like a fire hose). 37)
    • You can also use the same 1/8” plug hole to install a barb and clear hose to visually inspect for oil flow.
    • Check the pinion shaft to bushing clearance to the specs in the FSM.
      If the fit is overly loose, this condition will not allow oil to be transferred up the lines at low speed.
      Oil will just be bled out into the cam chest until RPM sends and over-runs more oil than can be spilled at the bushing.
      • If the fit is out of spec, you'll need to replace the bushing. 39)
      • Then line ream it using a special reamer through an old right-hand crankcase half to use to guide to get it in square.
    • On 76< motors, it's best to eliminate that possibility before spending time and money yanking the engine out of the frame and inspecting the oil pump.
      (and before spending money getting a new pinion bushing reamed with the special tooling etc.) 40)
  • The oil pump could be weak or malfunctioning.
  • 76< pumps:
    • If the pump shaft seal is blown, then the scavenge pump will continue to function because the pump pressure is higher than scavenge pressure. 41)
      So oil will flow from your pump down the shaft into the scavenge pump and goes back to the tank from there.
      It's possible the pump got some trash in it and got scarred and now just doesn't pump very well.
      It's a nasty job getting the thing off, made doubly nasty if you don't find anything wrong.
      If you have an oil flow problem from the pump, you can either rebuild it or put a new one on just to make sure that this is not the problem.
      If it isn't the pump, then start looking for leaks.

If oil is not returning to the oil tank:

Check the oil lines:

  • Pull the feed line from the engine / pump.
  • Verify that oil from the tank will voluntarily flow out the end.
  • If not (and the tank has enough oil), check the vent line.
  • The vent line runs from the tank into the crankcase where tank pressure is vented to atmosphere.
  • Verify this line is not pinched or stopped up (not allowing pressure to equalize in the tank).
  • Pull the line at the engine, induce air into the line and check that the air is coming into the tank.
  • Pull the return line from the engine / pump.
  • Place a spare hose on the return fitting and to a catch can.
  • Roll the engine over by hand and verify that oil will shoot out of the fitting.

Remove and inspect the oil pump.
The oil pump supplies pressurized oil into a hole in the cam cover.
That pressurized oil is forced up the lines (between the cylinders) to the rocker box by the oil pump.
That is the vertical end of responsibility (pressure wise) for the oil pump.
Before the oil reaches the rocker lines, it splits off to a hole through the pinion shaft (to get to the rod bearings).
This is the horizontal end of responsibility (pressure wise) for the oil pump.

With this pressure comes a certain amount of oil flow from the oil pump.
With a weak oil pump, there will be less pressure forced up the oil lines.
This will result in less oil reaching the rockers.
But, not necessarily less oil reaching the rod bearings (depending on degree of pump pressure reduction).
How much oil loss to the rockers is acceptable is yet to be determined.
However, the MoCo had to have accounted for a certain amount of pressure loss from the pump during the engineering phase.
But, the service limit for oil pressure was not detailed in the FSM.

  • The scavenge and / or feed side of the pump may be damaged or not working properly.
  • 77-85 oil pump checks.
    • Oil Pump check valve:
      • Check for a stuck closed check valve.
        • Open the pump cover and push a small screwdriver or suitable metal rod into the hole in the check valve.
        • The valve should be closed and the rod should push back on the internal spring with ease.
        • If it is stiff, remove the check from the pump body and then remove it's O-ring seal.
        • Soak it in solvent while pushing in and working the valve open and closed until it is easy to move with the rod.
        • If it won't spring back, replace the check valve.
    • Check that the feed and scavenge gerotors aren't damaged or scratched bad enough to warrant replacement.
    • Check that the gerotor keys (solid pins on the gearshaft) are not sheared.

Oil Pressure Switch

See also Testing the Oil Pressure Switch in the Sportsterpedia.

The oil pressure switch (for the oil light) is a pressure actuated diaphragm type on / off switch basically.
The diaphragm is spring loaded and held against its contact point when then engine is not running or the when the oil pressure is too low while running.
With the switch contacts touching, this closes the circuit to the oil pressure light and causes it to light up (with the key on, of course).
When the engine is fired up, oil pressure builds in the oil pump, activates the oil light switch and opens the oil pump check valve (allowing oil to enter the engine)
Oil pressure is sensed by the oil pressure switch.
By the time the engine reaches over 1000 to 1200 rpms, the oil pressure is sufficient to move the oil pressure switch diaphragm completely off it's seat.
This opens its contact point, breaking the circuit to the oil pressure light and it goes off.

Cold cranking oil pressure can reach between 30 PSI and upwards of 60-100+ PSI.
Oil pressure will vary from 4-15 PSI under normal riding conditions.
However, idle oil pressure will vary from 3-7 PSI.
So, at idle, the oil pump check valve is barely opened past it's cracking pressure (not to it's end of travel).

In the Case of a Defective Oil Pump Switch:
This switch opens and closes the contacts to the oil pressure light.
The oil light is important to have since if it is not working, it can be assumed that you have little to none oil flow to the engine.
If the pressure switch doesn't operate the light it should be checked for proper operation or replaced.
For the $30 or whatever you save by not buying the switch, it's just not worth it to not have the low engine pressure idiot light working. 42)
If your motor is ready to run and you need to test it then you can connect a piece of clear hose so you can see oil in it.
Don't plug the end till you've primed the pump (with ignition off kick it over a few times until oil comes out the clear pipe where the pressure switch lives).
Replace a defective switch as soon as possible.

Oil Pressure Switch Pics

Oil Pump Check Valve

The oil pump check valve plays a role in the operation of the oil pressure switch.

The check valve is not a pass through but instead a cartridge type one way check valve operated by a spring loaded cup against a seat pressing at 4-6 PSI.
Oil pressure enters the center of the check valve, lifts the cup against its spring and exits the check valve by pushing around and past the cup and into the engine.
At a point, the cup will float off it's seat up against the spring towards the end of it's travel.

According to the FSM, the check valve has two main functions;
It prevents gravity oil drainage from the tank to the engine when not in operation.
It also acts as a restriction to activate the oil pressure switch.

Without the check valve, the pressure would not build up as much in the pump.
It would free flow into the crankcase and disperse.
With the check valve installed and the oil having to find it's way around the cup, pressure builds behind it.
This back pressure builds inside the pump and pushes the pressure switch contacts open, shutting off the oil light.

The cup will stay off it's seat and open as long as there is sufficient oil pressure pushing against its spring.
This spring actuates the 4-6 PSI pressure that the pump must overcome.
If there is not enough oil pressure coming from the pump to keep the check valve cup completely or partially off it's seat;
The back pressure from the spring will push the cup toward it's seat, or closed position, equal to the amount of minimum pressure loss from the pump.

Until the seat is fully closed, the remaining oil pressure will still try to push past the cup.
At a point, the pressure from the pump will not be sufficient to completely float the cup off it's seat.
So, the cup will turn sideways a bit only allowing oil to pass it on one side.

This reduction in pressure is also sensed by the oil pressure switch.
When the pressure drops, the diaphragm eases back toward the closed position.
If the pressure is low enough, the contacts will close or partially make contact while closing or intermittently opening and closing.
The oil light will come on or flicker depending on the action of the contacts.

The pressure switch requires no back pressure from the engine to stay open.
It opens solely from the pressure generated from the oil pump with the assistance of the check valve to hold some of that pressure in the pump.
So, it is possible but not likely to have a stuck closed check valve with no oil light on.

Top End Oiling

Cam Cover Oiling

The oil going up to the top end not only passes by the bushing in the cam chest, but also is fed to and from the cam cover and through the cam cover gasket. 43)
It is possible for the gasket to blow out and seal up the oil galley feed passages.
Also if silicon was used on the cover, it is possible for that to break loose and stop up the passages.
You can take the cover off and run a tap down all the threaded holes to clear out any obstructions.
Also check that the face of the cover and case are not marred by some big scratch or dent.
To get old silicone out of bolt holes, you can use an inflation needle for footballs/basketballs/soccerballs. 44)
Cut the tip off of it then screw it into the end of an air blowgun.
It's narrow enough that it doesn't block debris from getting out of the hole.

Oil path of 85 style cam cover 45)

Oil Lines to the Rockers

There are rubber grommets on both ends of the oil lines. 46)
Some guys install two on each end, which is a wrong thing to do.
Sometimes the rubber from an improperly installed grommet plugs the oil line.
Before going into the gearcase (to check for low / no oil to the rocker boxes);
Remove both oil lines, and check the rubbers on both ends of each.

Oil line sleeves. 47)

Rocker Box

The feed to the rockers is not a large diameter passage and not a lot of oil goes to the rocker gear. 48)
But if you pull the lines off with the engine running you should be getting a good steady flow out of them.

Bottom End Oiling

Transfer Valve (76 and earlier)

The foregoing by Dr Dick 49)

The transfer valve is staked into position. 50)
Look very close around the edges and you'll see two spots that have been lightly punched.
If you clean the metal away from there with a sharp instrument it will come out fairly easily.

Transfer valve 51) Transfer valve location 52)

The purpose of the transfer valve is to keep your garage floor clean.
It's an oil control device to control the oil in order to keep it in your bike.
There is so much speculation on this subject that sometimes the myth becomes the reality.

  • The transfer valve is a part of a bigger system.
    A system that we often break down into its components.
    Then we deal with the (target component) often losing sight of the big picture.
    It's our nature as mechanical guys.
    Pin point the problem and then bring the hammers of Hell to bear on it.
    If we can let go of that instinct for a moment this will make perfect sense.
    So you want to think big picture here.
  • The Transfer Valve:
  1. Fact: If you blow thru the valve it only allows flow from primary to engine.
  2. Fiction: That means its a one way check valve. Bad assumption.
    It allows flow one way only when pressure is different one side of valve to other. See #3.
  3. Fact: When taken apart carefully as not to bend the triangular reed we find no spring that 'checks' the valve when pressure differential is absent.
    So it's allowed to 'leak' in state of equilibrium.
  4. Fiction: There's something missing from this valve.
    That's why its not checking and allowing leaking oil into my primary as I found when I left the primary cover off an saw the trail of oil from the valve.
    If you dismiss the assumptions and stick with what we can prove this truth emerges:
    The transfer valve is a one way feed when engine is running but not when engine is static.
    (then it's relaxed and oil leaks from motor thru it)
  5. Fact: Oil is leaking out of your valve when the primary cover is off.
    (it's leaking when the primary cover is on too)
  6. Fiction: There's only supposed to be a small amount of oil in the motor so there's something else wrong too. What could that be?
    Aha, it's got to be the check valve in the oil pump leaking.
    (This is the spot you go off course chasing ghosts. Because your motor is not running, oil is leaking into it before it even gets to the check valve).
  • You are told to inspect the check valve in response to any noticeable change that increases oil exiting thru the breather tube.
    Because a check that leaks will shorten the time it takes to fill the motor enough to puke.
  • Even a perfectly sealed check can't stop oil that's getting in thru a different path.
  • If we slow down now and think, we get to this:
    In order for the pump check to leak, oil has to get to the tank side of pump check.
    In order to get there its got to sneak past gear clearance in pump (which it obviously does).
    But this is not the only place this errant oil can go:
On the way to the check, it finds clearance here, where
the breather valve fits thru the upper oil pump housing.
Where it leaks into the space between the breather
sleeve and housing, exiting at the first place it can
(the bottom of slot in the upper housing).
Now, it's filling the breather passage that leads to the
crank case. This passage is located lower than
the floor of the cam chest.
  • So, oil is now filling the crankcase and not the cam chest.
    The factory made sure that it happened like this.
    They wanted this unchecked oil to stay out of the cam chest so that your bike is less likely to puke oil.
  • They didn't want the oil to just sit in the case sump either because it would just end up in the cam case soon after the bike was started.
  • They wanted to somehow 'transfer' it to a reservoir allowing it to re-enter the engine in a controlled volume that the return pump could handle without being drowned.
Look at the position of the valve compared to the
breather passage. It's about even.
Go back to the 1st case pic. Note, the floor of the cam
chest is about even to the bottom of the pinion race.
Now look at the position of breather passage in
regards to floor of cam chest. Chest floor is higher,
breather passage lower. Crap flows downstream.
  • So oil flowing unchecked into the pump from the oil supply line leaks clear thru engine into primary before it can start to fill the cam chest.
    On the primary side though, there is plenty of room to fill with the errant oil.
  • The transfer valve 'transfers' “pre pump check” oil leakage out of the motor and into the primary.
    Where it re-enters the engine on startup in a controlled volume that the return pump could handle without being drowned.
  • In other words, it 'transfers' it back to engine when bike starts.
  • This is the improvement refined from the 52-54 siphon tube that used the same valve guts.
  • It does makes perfect sense don't it?
  • Now, given some thought you will see why the valves aren't used on the racers.
  • The '77 style oil system did away with the unchecked supply leakage. (so there is no reason to 'transfer' what isn't there).
  • It's name is absolutely 100% correct: It's the transfer valve.
  • The factory 'got it right' with this part. 
  • Keep an eye on the big picture.

Wet Sumping

See article on Wet Sumping in the REF section of the Sportsterpedia

1986-1990 HD Sportster FSM pg 3-42
13) , 14) , 15) , 16) , 17) , 18)
1959-1964 HD Sportster FSM pg 3A-15
19) , 20) , 21) , 22) , 23) , 24) , 25) , 27) , 28) , 29)
1970-1978 HD Sportster FSM pg 3-7
1970-1978 HD Sportster FSM pg 3-5
1959-1969 HD FSM pgs 3A-11, 3A-15
HD 70-78 FSM pgs 3-1, 3-5
1979-1985 HD FSM pgs 3-1, 3-10
34) , 35)
photo by Dieselox4 of the XLFORUM http://xlforum.net/forums/showthread.php?t=1456449
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