Sportster Gerotor Oil Pump Overhaul
Text and Pictures by Mark Trotta
First seen on 1977 models, the gerotor oil pump was well designed and stayed in use until the end of Sportster production. When overhauling an older engine, the only way to know it's true condition is disassembly and inspection.
NOTE: Before the pump is removed, there will be noticeable friction while turning the top oil pump gear by hand. This is normal and OK, and here's why. To maintain zero side clearance, a spring presses against the inner plates in the pump. This is the drag you feel when you turn it.
Once the four bolts and the pump are removed, the shaft should spin easier.
Removal
Unless other services are being performed, like replacing cams or a bottom end overhaul, the engine gearcase cover does not need to come off.
Disconnect and tag the oil lines, then remove the four mounting screws that hold it to the crankcase.
Once off the bike, the cover should lift off the body. If it's stuck, don't try to pry it or force anything. To avoid damaging the soft alloy body, try some penetrating fluid (like WD40), or soaking the entire pump in a gallon of carburetor cleaner.
If you end up soaking it, any rubber parts, such as O-rings, will have to be replaced. All parts needed for a rebuild are included in an oil pump overhaul kit.
Gerotor pumps consist of rotating inner and outer gears. The Sportster gerotor oil pump has two sets of gears (feed and return).
The first pair of gears that come out are the feed gerotors (#13 in diagram).
There is a circlip and a roll pin on the gear shaft. You'll need a pair of needle nose pliers to pull the roll pin out.
With a pair of external lock ring pliers, remove retaining ring from gear shaft.
Also on the gear shaft is an outer plate, outer plate seal, and spring washer.
The 2nd pair of gears to come out are the return gerotors, which are thicker than the feed gerotors.
Check Valve
The oil pump check valve contains a spring-loaded cup. It is designed to maintain 4-6 psi of oil pressure.
After removing the small O-ring, the check valve can be pushed out of the housing.
Parts Inspection: What To Look For
After cleaning (brake parts cleaner and shop towels work well), inspect all parts for re-use.
Check that the spring-loaded cup in the check valve moves freely.
Check for excessive scratching of the cover where the feed gerotors sit, as well as the tops and bottoms of gears.
Check that the spring washer has no broken 'fingers'.
If your oil pump shaft has worn or damaged teeth, you can buy a replacement here.
Inspect all gears for wear. Light grooves on the gears indicate normal wear. Deep grooves are considered excessive. It's recommended that inner and outer gerotor gears to be replaced as a set.
Measure Tip Clearance
Mesh both rotors together, and measure clearance between tips of lobes.
If tip clearance is over .004" they are worn past recommended tolerance and gears should be replaced as a set.
New Oil Pump Replacement
If it looks like yours will not be rebuildable, V-Twin Mfg. offers a new Oil Pump Assembly which replaces OEM 26197-83 and fits all 1977 through 1985 Sportster models.
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Assembly
The following assembly procedures were taken from my well-worn factory service manual:
Install gear shaft through housing, then press roll pin into place with needle nose pliers.
Coat all internal parts with engine oil.
Insert inner (thicker) gerotor over gear shaft. Install new circlip with external lock spring pliers.
Install new seal into outer plate, so that the seal lip will be toward feed gerotors. Place outer gerotor over inner.
Install inner plate and line up for slot in pin. Place spring washer on inner plate.
Gently push outer plate over gear shaft, then place gerotor set over gear shaft.
Install new O-ring over check valve and push into place. Note the arrow on the check valve. Make sure it is pointing in direction of oil flow.
Place a new O-ring into groove between valve and pump body.
Place a new O-ring in groove in cover and place onto pump body.
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According to the FSM, the pump to case mounting gasket is to be coated with gasket sealer. This is a debatable topic, as many builders find it unnecessary.
Tighten four mounting screws to 90-110 Inch/Pounds.
Notes and Misc
Unlike 1976 and earlier Ironheads, breather timing is not required.
1977-1985 feed gerotors are the same size, with the exception of late-83 and up, which has a chamfer on the outside of the set.
Priming Oil Pump
Whenever an oil pump is removed, it needs to be primed before starting the engine. Loosely install oil pressure switch. Crank or start engine and allow about two ounces of oil to come out. When done, remember to tighten oil pressure switch.
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Oil Pump Repair Kit
James Gasket Oil Pump Repair Kit includes all parts needed to overhaul 1977 through 1985 Harley Sportster oil pumps.
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