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⁾

• There are 3 basic pumps
  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:
  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.

• All these use 16t gear sets and style 1 plumbing
• The production changes made during its run:
  • 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.
• All use half moons and shortened key on scavenge drive.
• Bodies made till '66 are for style 1 plumbing.
• In '67, the body gets tapped for the external feed fitting for use on 67-69 XLH. This is when style2 plumbing started.
• Bodies tapped for style2 were still used on the last 3 yrs (67-69 xlch) of style1 cases.
• A plug is put in this new hole if body got used on a style1 case set.

goes back to 16t gears. and snap ring with long key 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. body and breather housing get an extra hole (2 holes now) drilled in them for addl return capacity. cases also get extra matching hole. solid feed gear drive pin gets replaced by the hated roll pin. dowels between body and breather housing are now history.

gonna break each complete pump into these components 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.

pics of parts: (sorry i dont have all of the different parts handy. missing -56 breather gear and long full profile woodruff scavenge drive key and snapring)

breather gears.

below: some of amf's signature quality control. these are 3 -72 breather gears.

a closer view

nice huh.

the 2 different breather housings

more often than not the solid pin was a slipfit in cross hole.

on to the bodys

the 2nd text is “26217-56a L58-e62” i will work on gettin a bigger pic for the above.

the 4 different scavenge gear sets. lined up from early in foreground to later in background. this is to show the height progression.

top view of all 4 sets.

a closer view of the height changes.

• 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 form 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⁾