IH: Oiling & Lubrication - Sub-03C

77-85 Oil Pump Damage and Repair

Cracks in Housing or Cover

This cover was cracked at the oil pressure switch end.
The crack was welded over and a Dremil tool was used to reshape the cover.
Due to warpage during welding, the threads need to be chased with a tap to straighten them back out.

Repair on oil pump cover 1) Oil Switch Torque 2)

Scratches on Gerotors or Mating Surfaces

  • Many used oil pumps have scratches on both the gerotors and pump surfaces that the gerotors ride on.
  • But, there is one certain spot that seems to be scratched more times than others. 3)
    • It's on the larger of the two pads in the pump body and the cover seem to usually have more wear.
    • Sometimes, the small pad is scratched or damaged also but not always.
    • The gap between the inner and outer gerotors on both the feed and return sides tends to be scratched as in the pics below.
    • Debris caught between these two gears cannot slide over and fall to the other cavity and out of the pump.
    • It gets locked between the gears and ripped across the aluminum surface.
  • In theory, no particles of any size should be able to spin around to the small pad due to the pressure generated by the spring washer and the gerotor spacing there.
  • Also, any debris picked up from the source side cavity should drop down into the feed side cavity and out of the pump.
  • The side toward the motor is where oil is transferred to and from the pump.
  • The inner and outer gears come together on the other side (right side).
  • This spacing relationship doesn't change between the motor side or the outside of the pump due to the offset gearshaft.
  • But in reality, debris gets caught in or between the gears and gets dragged over the aluminum flats.
    • Some then find their way under the gerotors while the spring washer flexes from the stress.
    • The debris spins around under the gerotors and wears scratches in the flats (pads) or worse.
Gerotor rotation 4)
Oil pump from an 83 model 5) Gearshaft pin broke off into this 77 model 6)
  • There should be some reduced pressure because of the scratches.
  • Pressure generated to the output cavity can squirt back to the input side through these scratches.
  • How much pressure loss would depend on the width, depth, length of the scratches and oil viscosity.
  • To make the pump inoperative or not make pressure (from the scratches alone);
    • The scratches would have to be proportional to the relative volume of all four gerotor reservoirs combined.
    • Then, the check valve would have to accept less pressure flow than the backpressure from the pump.
  • The gerotor surface in the cover would have to be eat up pretty bad to make the pump completely ineffective.
  • The pump would have less pressure loss with multi-weight or straight weight oil when cold than hot.
  • They'll both flow faster when hot.


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