From 1972 to 1989, the gear driven oil pump has went through several changes with the main body and design staying the same as in the ball check valve assembly and seals: ¹⁾

• 1972 - Feed pump speed was 1/4 of the engine speed and the return side operated at a 2:1 ratio of the feed side. The breathing system was used to return oil from the crankcase into the cam/ gear cover where the oil drained directly onto the return gears of the oil pump.²⁾
• 1975-1980 - The engine had a separate oil sump bolted to the crankcase. Return gears scavenged the crankcase oil through an external oil line.³⁾
• 1989-2003 - Using the same design of the '75-'80 pump, but with a more efficient drive gear design and improved oil routing, the oil pump speeds were doubled to 1/2 of engine speed for the feed pump and a 4:1 ratio on the return side. The oil pump drive gear was re-activated as a breather only. ⁴⁾

• The separate oil feed and scavenger (oil return) pumps are gear-type pumps and are incorporated in the same pump housing with a check valve on the oil feed side. The feed section is gravity fed from the oil tank and forced fed from the pump to the engine and back to the scavenger side of the pump which returns oil back to the oil tank. ⁵⁾
• In a gear type oil pump, the oil is transferred from the inlet to the outlet side of the pump when it is trapped between the rotating gear teeth and the gear housing.
• The oil pump seldom needs servicing. Therefore, before dis-assembling it for repairs because of no oil pressure, be absolutely certain that all possible related malfunctions have been eliminated. ⁶⁾
  • If oil in oil tank is diluted, pressure will be affected.
  • In freezing weather, the oil feed line may clog up with ice or sludge, preventing circulation.
  • Inspect oil pump check valve as it prevents the gravity flow of oil into the crankcase when the engine is not running and provides the correct oil pressure for the operation of the oil signal light switch. If the check valve is not seating properly, oil will bypass the valve and drain oil from the oil tank into the crankcase and upon starting the engine, a considerable amount of oil will be blown out the crankcase breather pipe.
  • Check for a grounded oil pressure switch wire or a faulty switch if oil indicator light fails to go out with the engine running.
  • If no oil pressure or return oil is not indicated at the oil tank, when engine is running, or an excess amount of oil is blown from the breather pipe, dis-assemble the oil pump for repair. Damage can occur by way of a foreign object lodged in the oil pump gearing. Check your FSM for dis-assembly and repair. ⁷⁾

• The oil pump is fitted with gerotors instead of gears consisting of two gerotor pumps in the same pump housing. The pump is gravity fed from the oil tank. The feed pump forces oil to the engine while the scavenger pump collects and returns oil back to the oil tank.
• A gerotor type pump has 2 elements, an inner (which always has one less tooth than the outer) and an outer gerotor. Both elements are mounted on fixed centers but are eccentric to each other. ⁸⁾
• In a gerotor type pump, oil is transferred from the inlet to the outlet as it is trapped between the rotating inner and outer gerotors. ⁹⁾
• During the first 180 degrees of rotation, the cavity between the inner and outer elements gradually increases in size until it reaches it's maximum size which is equal to the full volume of the missing tooth. The gradually enlarging cavity creates a vacuum into which the oil flows out from the inlet. During the next 180 degrees of rotation, the size of the cavity decreases forcing oil into the outlet.¹⁰⁾
• Oil is forced into a valve with a one way spring loaded cup set at 1 1/2 psi. From that valve, oil exits the pump and enters the crankcase. Oil pressure is indicated by the oil pressure switch. ¹¹⁾

• There are 3 basic pumps ¹²⁾
  1. 57-E62 (3 variations) these use 16t body gears.
  2. L62-71 (2 variations) these use 14t
  3. 72-76 (no variations) use 16t again
• & 2 basic plumbing styles: ¹³⁾
  1. Both feed and return are drilled passages in the right crankcase (57-66 all) & (67-69 xlch)
  2. Only return drilled thru case. feed goes from tank to pump by external hose. (67-69 xlh) & (70-76 all)
• With the correct knowledge any 57-76 pump, or parts of them can be mated to any 57-76 cases. But the combos can get confusing. ¹⁴⁾
• The stock slot in pre & post -72 pump bodies are .345“ ¹⁵⁾
• The stock slot in pre -72 pump gear is .375” ¹⁶⁾
• The stock slot in post -72 pump gear is .625“ ¹⁷⁾

• All these use 16t gear sets and style 1 plumbing ¹⁸⁾
• The production changes made during its run: ¹⁹⁾
  • 57-e58 baseline pump that all others came from. no oil seal. uses a snap ring and a full profile woodruff key at scavenge gear.
  • L58-59 same as above but now has body machined for a oil seal.
  • 60-e62 same as L58-59 but the retaining ring at the scavenge is replaced by half moon retainers. The scavenge drive gear is counter-bored for these half moons and the woodruff key is shortened so it won't interfere with the half moons.

• All these used 14t gears & scavenge sets got taller than the previous 16's were. ²⁰⁾
• All use half moons and shortened key on scavenge drive. ²¹⁾
• Bodies made till '66 are for style 1 plumbing. ²²⁾
• In '67, the body gets tapped for the external feed fitting for use on 67-69 XLH. This is when style2 plumbing started. ²³⁾
• Bodies tapped for style2 were still used on the last 3 yrs (67-69 xlch) of style1 cases. ²⁴⁾
• A plug is put in this new hole if body got used on a style1 case set. ²⁵⁾

1967 XLCH Oil Pump 26)

• These go back to 16t gears and a snap ring with long key ²⁷⁾
• Feed gears are the same as 57-e62 but the scavenge set is now wider again (wider than any of the previous sets).
• Breather gear gets enlarged slots in it. ²⁸⁾
• Breather timing:
  • Open 20-25 deg ATDC Front CYL ²⁹⁾
  • Close 85-90 deg ABDC Front CYL ³⁰⁾
• Body and breather housing get an extra hole (2 holes now) drilled in them for additional return capacity, cases also get extra matching hole. ³¹⁾
• Solid feed gear drive pin gets replaced by the hated roll pin. ³²⁾
• Dowels between body and breather housing are now history. ³³⁾

• Each complete pump breaks down into these components: ³⁴⁾

1. Breather or sleeve gear-has the 2 slots in it
2. Breather gear housing- cast iron part that breather rides in
3. Feed gear set and drive pin (the skinnier of the 2 gear sets)
4. Pump body
5. Scavenge gear set and drive key and retaining clip.

Click on a pic to enlarge:

(Missing are the -'56 breather gear and long full profile woodruff scavenge drive key and snap-ring). ³⁵⁾

Breather Gears 36)	Some of amf's signature quality control. These are 3 - 72 breather gears.37)	A closer view38)

The 2 different breather housings39)	Feed Gear Sets40)	More often than not the solid pin was a slipfit in cross hole.41)

On to the bodies. The 2nd text is “26217-56a L58-e62”42)

The 4 different scavenge gear sets. Lined up from early in foreground to later in background. This is to show the height progression.43)	Top view of all 4 sets.44)	A closer view of the height changes.45)

With the replacement of the gear driven oil pump by the new gerotor style pump, HD issued a recommendation to dealers regarding servicing of the new style oil pumps. ⁴⁶⁾

• Zero gerotor (gear) side clearance must be maintained by the flat spring located between the upper and lower gerotor sets in the oil pump to provide adequate oil pressure. For the spring to function properly, the upper face of the lower feed gerotors must extend slightly above the cover to prevent any side clearance which would allow oil to get past the gerotors and reduce oil pressure. ⁴⁷⁾

• If you encounter reduced oil, no oil pressure (oil pressure light comes on or stays on) or otherwise need to disassemble the oil pump for any reason, the gerotors should be checked and serviced. ⁴⁸⁾
• Using a straightedge across the feed gerotor set (installed) surface, measurement should be taken with a feeler gauge from the gerotor surface to the ridge of the edge of the aluminum cover:
  • The thin, feed gerotors (26492-75) are in the oil pump cover (26486-75) and should extend .001” - .005“ above the cover's aluminum ridge which surrounds them. ⁴⁹⁾
  • The later gerotors extend up to .011” above the ridge. If the feed gerotors do not extend above the ridge within the specified range, remove them, lay some sandpaper (#280 grit to start - #400 grit to finish), invert the cover and sand the ridge evenly until the gerotors extend properly when inserted. Check the measurement with a micrometer to see that both the inner and outer gerotors are the same thickness. ⁵⁰⁾
  • If the widths measure equally but the gerotors are not equal in height when placed into the cover, then the cover surface is not flat and the cover should be replaced. Be sure to check the gerotors in the new cover using a straight­ edge to assure a level surface and the proper elevation above the ridge. ⁵¹⁾
• Another possible cause of low oil pressure is air leakage into the pump due to a loose hose clamp at the oil pump feed hose fitting (63540-62) and at the oil tank feed hose fitting. If the existing feed hose clamp (10020) cannot be evenly and securely crimped to the fittings, remove the clamp and install a worm drive hose clamp. This will prevent air leakage into the system which could cause loss of oil pressure due to an airlock in the oil pump. ⁵²⁾
• Oil pump covers found with an uneven gerotor surface should be removed. ⁵³⁾

77 Oil Pump Parts 54)

79 Oil Pump 55)

• The late 83 oil pump assembly (26197-83) gerotor gears are fabricated without the chamfered top and bottom on the outer diameters as was in the 77-E1983 gerotors. This new assembly will retrofit to 77-E83 ^{56) 57) 58)}
• Late 1983 pump bodies and covers were also under-cut or relieved to accommodate for clearances with the new gerotors.
• The 77-E83 chamfered gerotors have a (.020“ x 45° chamfer or .020”) radius and the same radius is designed into their respective oil pump body / cover.
• The Late 83 pump body and cover has a (.010“ Max.) undercut for clearance designed into them.
• These modifications limit interchangeability and affect the installation of repair parts:
  • Either early style or late style gerotor gears may be used with late style (under-cut) oil pump bodies and covers.
  • Only early style chamfered gerotor gears may be used with early style oil pump bodies and covers (Use of late style gerotor gears in early style oil pump bodies and covers could cause the oil pump to bind up and possible pump failure).

The foregoing by Dr Dick ⁵⁹⁾

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 some thing 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 primary cover is off. It's leaking when 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.