• The 86-90 gerotor pump can be removed with the engine in the frame and the gearcase cover installed.
  • Disconnect the oil lines.
  • Remove the four mounting bolts and the pump should drop down.
  • There is a flat spot on the frame just under the pump. ²⁾
  • The complete pump assembly comes out as a unit.
    • It´s not possible to take only the cover out because of the of limited space between the cover and frame. ³⁾
  • Its a tight squeeze but you can wriggle the pump out. ⁴⁾

The 86-90 oil pump is the next generation from the ironhead (77-85) pump.
The FSM's for those year pumps say to apply gasket sealer to the gasket before installation.
The 86-90 FSM leaves this step out. However, the practice did continue.
So the pump may be stuck to the engine case after the bolts come out.

There are also times when a gasket could not be found, so RTV or other sealers were used in addition to or instead of a gasket. ⁵⁾
Either way, if gasket sealer was applied, expect that to make it more difficult to remove the pump from the engine.

• First, be patient with it.
  • Try to turn the motor over by hand. It may push the pump out. ⁶⁾
  • Try a rubber mallet.
    • Gently tap down on the pump's rear side so you're not forcing extra pressure against the drive gear on the pinion shaft.
  • Try a short piece of 2×4 to gently tap on the pump.
  • Try using a crowbar with a “catspaw” on the rear side of the pump.
    • It's a wood working tool for pulling nails. ⁷⁾

There are several ways to remove a stuck gasket.
The use of metal abrasives on aluminum mating surfaces can result in distortion or scratching of the surface and a possible leak thereof.
A straightedge razor blade can cut ruts in the surface guaranteeing a leak.
Plastic scrapers and elbow grease is good alternative.
Soaking the gasket with a solvent will soften it somewhat so removal is easier.
However, the outer plate and cover seals will have to be replaced before reinstallation.
You may have to soak it and scrape several times while removing gasket layers.

Below PB Blaster was used with an auto window scraper. ⁸⁾

The spring washer inside the pump puts a lot of tension against the cover.
This pressure should push the cover off of the body when the pump assembly is removed from the engine.
Although in use, oil glazing will build around the mating surface between the oil pump body and cover from heat and time.
So, it is common for the cover to be stuck to the pump body.

According to the FSM, the pump to case mounting gasket should be coated with gasket sealer before installation.
This is a debatable procedure as many have reported that is not necessary.

However, sometimes people will also apply sealer to the cover O-ring or the channel that the O-ring sits in.
This later makes separating the cover from the body more difficult.

• Try holding the pump body in one hand and twisting the cover with the other hand.
• Try laying the body on the corner of a wooden table (cover hanging off the wood) and gently tapping the cover to twist it.

79 oil pump 9)

For whatever reason, the cover can be stuck bad enough that it will not come off by tapping it with a rubber mallet.
Before using a screwdriver or prybar;

• Try soaking the entire pump in solvent (as in a gallon of carburetor cleaner).
  • The pump will fit in the small bucket that's inside the gallon can.
    Make sure to remove the oil pressure switch before soaking.
    Also check the label for safety precautions.
    
  • Keep in mind, any rubber parts on the inside will have to be replaced before reinstallation.
    The solvent will soften and expand the cover O-ring and outer plate seal and render them useless.
    
  • Drop the oil pump in the bucket, lower the bucket into the can carefully so as not to splash the solvent and close the lid.
  • Depending on how old or how 'stuck' the parts are, soaking for a couple hours may help to separate the old gasket in between.
  • However, a 24 hour soak will help to soften the gasket / sealer and make it easier to break free.

Carburetor Cleaner 10)

• After soaking, open the lid, remove the small bucket inside by the handle, set the bucket on the ground and wash the parts cleaner off with a water hose.
• Let them air dry and most, if not all of the grease/grime should be gone.
• You may have to re-soak heavy grimed parts or use a wire brush to break grime hardened areas before soaking again.

This oil pump had to be soaked overnite before the cover would separate from the body.

Cleaning and soaking gaskets for more easy removal 11)