In the wake of multiple Threads lately concerning Questions about the Gerotor Oil Pump and its ancillary Seals and Pick Up Tube Issues, here are the ‘Complete Autopsy Images’ of the Pump along with all of the Dope on What this Pump Does… How it Works… and What its Modes of Failure are:
https://www.flickr.com/photos/126111508@N07/albums/72157713216978312/with/49571444046/
(1) The GM Atlas 4.2L LL8 Gerotor Pump is Mounted to the Inner Timing Cover. The Crankcase-Oil-Pan and Timing Cover MUST be removed prior to it being accessed and serviced. The Gerotor Oil Pump derives its Power from a Crankshaft Mounted Sleeve Gear that Keys Over a Single Steel Pin inserted into the nose of Crankshaft. The Gerotor Oil Pump is held in place by (7) Torx T-30 10.9 Hard Machine Screws that need to have Hi-Temp Thread-Locker applied to their Threads along with a MAX of 106 Inch Pounds of Torque. When removing the Gerotor Oil Pump Cover… the In-Dwelling Gerotor Gears should next be wiped down with Brake-Kleen Spray on a Rag and immediately Marked with a Permanent Magic Marker to locate these Gears in their ORIGINAL POSITIONS on the Two Inner Gear Segments prior to removal and cleaning of the Inner Oil Cavity of the Timing Cover. When replacing these Gears...Remember to install them both with the Beveled Edges toward the INSIDE of the Timing Cover Cavity... AND Soak them Down In Motor Oil FIRST.
(2) The Early Models of the 2002-2004 GMT-360s with the 4.2L LL8 Engine employed a Gerotor Oil Pump having a Shallow Beveled Inlet Manifold at its base and employed a “BLUE” Viton “O” Ring with a short-snout Oil Pick Up Tube. The Later Model Gerotor Oil Pump sports an After-Market (MELLING) Longer Inlet Tube, with a Deeper Inlet Port at the Base of the Oil Pump and uses an Orange Rubber Impregnated Metal Grommet-Gasket as the means to solve a problem with a Design Failure of the “BLUE” “O” Ring Seal on the First Generation Pumps.
(3) The Crankshaft Gear feeds into the middle of a Combination Small-To-Large Gerotor Gear Set contained inside of the Gerotor Gear Pump Housing Rotating Steel Sleeve. These Three Gears work to Propel the Engine Oil from the Wide Spacing in the Open Gearing areas leading to Smaller and Smaller Spaces while attempting to compress the in-compressible Oil Fluid. This action serves to build up Oil Pressure, thus advancing this Oil Stream up, through and out of the Pump and into the Engine Block Oil Galleries. This Animation shows how different the Gerotor Pumping Design is from how The Old Matched Gears, Camshaft Helical Gear Driven Oil Pumps work:
(4) The Gerotor Oil Pump Cover is held flush, with NO SEALANTS OR GASKETS in between its smooth facing Flange and the flat, smoothly machined inner surface of the Inner Aluminum Timing Cover. This area of the Timing Cover forms an Oil Collection Chamber that fills with Motor Oil getting vacuumed up from the Oil Pick Up Tube attached at the Base of the Gerotor Pump Manifold. As the Motor Oil is advanced and fed into the Gerotor Gears...it forms a Strong Vacuum that in combination with Capillary Action always present between the Oil Molecules for additional help… Pulls the Motor Oil Up from the Lower Crankcase.
(5) The Gerotor Oil Pump is fitted with an Oil Pressure Relief Chamber and Plunger-Piston-Valve that consists of a Smooth Bore in the Cast Aluminum Body of the Pump that holds a High Grade, Hollow Steel Cup-Plunger fitted with a Strong Coiled Spring. The Nominal Oil Pressure for the Atlas LL8 Engines is 12 PSI at an Idle of 1,200 RPM and 65 PSI at 3,500 RPM. The Coil Spring is held in place by an Aluminum Screw Cap with a 5/16” Hex Wrench Hollow Center. Likewise… the Threads on this Hollow Aluminum Cap MUST also have Hi-Temp Thread Locker applied. Do NOT Exceed 89 Inch Pounds of Torque on the HEX-Cap as this is an Aluminum to Aluminum Fastener.
(6) In order to Remove the Gerotor Oil Pump HEX-CAP holding in the Plunger Spring… the (7) Torx T-30 Gerotor Oil Pump-to-Front Timing Cover Machine Screws MUST be unwound and the Outer Pump-Cover-Assembly MUST be removed FIRST. The reason for this is because there is a LEDGE Cast into the Lower Horizontal Flange of the Aluminum Front Timing Cover-Gerotor-Oil-Pump Assembly designed in as a “Last Ditch” effort to keep the HEX-CAP from completely coming off of its Screw Mount over the Coiled Spring should it become loose. It IS possible to insert the 5/16” Hex Wrench Socket into the Hex Hollow of the Aluminum Screw Cap... but as the the Cap is being Unwound Counter-Clockwise… that small Cast Aluminum “Ledge” WILL Break Off that Piece of the Lower Aluminum Flange.
(7) The Gerotor Oil Pump is capable of Pumping 11 + Gallons of Motor Oil Per Minute during its normal operation. However, if the Oil Pressure were to exceed 65 PSI… The “Lost Foam” Cast Aluminum Engine Block Oil Galleries could be overcome by Excessively High Oil Pressure ...and Crack them Open like Egg Shells (Edited as per Instructions after Peer Review by @Sparky and @Mooseman NOT to include Personal or Speculative Information... Thank You, Gentleman.)
(8) The Oil Pressure Relief Valve is designed to use its Plunger or Piston to squeeze down against the Strong Spring just enough to allow the Over-Pressurized Motor Oil to By-Pass the Main Oil Pick Up Chamber and return the Oil to the Incoming side of the Oil Pump. This happens automatically and even though the Plunger-Piston is in the constant presence of the lubrication offered by the Engine Oil… if Sand, Grit or Metal Particles get Vacuumed into the incoming Oil Stream...Those Gritty Particles CAN get JAMMED in between the Steel Plunger-Piston and the Aluminum Bore and cause the Plunger to cant sideways and get JAMMED AND STUCK INSIDE of the Bore.
(9) If this Stuck Open Oil Pressure Relief Valve event lasts for even a small amount of time, a Catastrophic Drop In Oil Pressure can put the Engine Cylinder Walls, Pistons, Rings, Crankshaft and Connecting Rod Bearings at risk of Seizing Up. IT IS VERY IMPORTANT TO REALIZE THAT THE OIL GETTING VACUUMED UP FROM THE LOWER CRANKCASE AND FLOWING IMMEDIATELY INTO THE GEROTOR OIL PUMP IS UNFILTERED.
(10) It will NOT be Possible to Remove the High Grade Steel Plunger-Piston through the Upper Threaded Bore in the Base of the Gerotor Oil Pump as that component is TRAPPED below the Thread Lines for the HEX-CAP. However, It WILL be possible to use a Pencil Magnet to Check the Piston for Freedom of Movement gliding in and out in that Chamber. But If that Piston is found to be JAMMED solidly inside the Body of the Gerotor Oil Pump… REPLACING THE GEROTOR OIL PUMP & TIMING COVER CASE AS A COMBO-UNIT: GM Part # 126 28565 should be considered. An Alternative choice is to keep the Timing Cover Case and ONLY replace the Gerotor Oil Pump using the Sealed Power Kit Part # 22453582 which includes the Inner Gerotor Dual Gear Set, The Outer Pump Cover, the (7) 10.9 Hard T-30 Torx Fasteners and the all important Oil Pump to Engine Block Black Rubber Grommet-Seal. Before Installing the Dual Gerotor Gear Set into the Front Timing Cover Inner Cavity... Soak them both down in Motor Oil.
The Gerotor Oil Pump Autopsy Images can be seen as linked below via my “Flickr-Bucket”:
https://www.flickr.com/photos/126111508@N07/albums/72157713216978312/with/49571444046/
https://www.flickr.com/photos/126111508@N07/albums/72157713216978312/with/49571444046/
(1) The GM Atlas 4.2L LL8 Gerotor Pump is Mounted to the Inner Timing Cover. The Crankcase-Oil-Pan and Timing Cover MUST be removed prior to it being accessed and serviced. The Gerotor Oil Pump derives its Power from a Crankshaft Mounted Sleeve Gear that Keys Over a Single Steel Pin inserted into the nose of Crankshaft. The Gerotor Oil Pump is held in place by (7) Torx T-30 10.9 Hard Machine Screws that need to have Hi-Temp Thread-Locker applied to their Threads along with a MAX of 106 Inch Pounds of Torque. When removing the Gerotor Oil Pump Cover… the In-Dwelling Gerotor Gears should next be wiped down with Brake-Kleen Spray on a Rag and immediately Marked with a Permanent Magic Marker to locate these Gears in their ORIGINAL POSITIONS on the Two Inner Gear Segments prior to removal and cleaning of the Inner Oil Cavity of the Timing Cover. When replacing these Gears...Remember to install them both with the Beveled Edges toward the INSIDE of the Timing Cover Cavity... AND Soak them Down In Motor Oil FIRST.
(2) The Early Models of the 2002-2004 GMT-360s with the 4.2L LL8 Engine employed a Gerotor Oil Pump having a Shallow Beveled Inlet Manifold at its base and employed a “BLUE” Viton “O” Ring with a short-snout Oil Pick Up Tube. The Later Model Gerotor Oil Pump sports an After-Market (MELLING) Longer Inlet Tube, with a Deeper Inlet Port at the Base of the Oil Pump and uses an Orange Rubber Impregnated Metal Grommet-Gasket as the means to solve a problem with a Design Failure of the “BLUE” “O” Ring Seal on the First Generation Pumps.
(3) The Crankshaft Gear feeds into the middle of a Combination Small-To-Large Gerotor Gear Set contained inside of the Gerotor Gear Pump Housing Rotating Steel Sleeve. These Three Gears work to Propel the Engine Oil from the Wide Spacing in the Open Gearing areas leading to Smaller and Smaller Spaces while attempting to compress the in-compressible Oil Fluid. This action serves to build up Oil Pressure, thus advancing this Oil Stream up, through and out of the Pump and into the Engine Block Oil Galleries. This Animation shows how different the Gerotor Pumping Design is from how The Old Matched Gears, Camshaft Helical Gear Driven Oil Pumps work:
(4) The Gerotor Oil Pump Cover is held flush, with NO SEALANTS OR GASKETS in between its smooth facing Flange and the flat, smoothly machined inner surface of the Inner Aluminum Timing Cover. This area of the Timing Cover forms an Oil Collection Chamber that fills with Motor Oil getting vacuumed up from the Oil Pick Up Tube attached at the Base of the Gerotor Pump Manifold. As the Motor Oil is advanced and fed into the Gerotor Gears...it forms a Strong Vacuum that in combination with Capillary Action always present between the Oil Molecules for additional help… Pulls the Motor Oil Up from the Lower Crankcase.
(5) The Gerotor Oil Pump is fitted with an Oil Pressure Relief Chamber and Plunger-Piston-Valve that consists of a Smooth Bore in the Cast Aluminum Body of the Pump that holds a High Grade, Hollow Steel Cup-Plunger fitted with a Strong Coiled Spring. The Nominal Oil Pressure for the Atlas LL8 Engines is 12 PSI at an Idle of 1,200 RPM and 65 PSI at 3,500 RPM. The Coil Spring is held in place by an Aluminum Screw Cap with a 5/16” Hex Wrench Hollow Center. Likewise… the Threads on this Hollow Aluminum Cap MUST also have Hi-Temp Thread Locker applied. Do NOT Exceed 89 Inch Pounds of Torque on the HEX-Cap as this is an Aluminum to Aluminum Fastener.
(6) In order to Remove the Gerotor Oil Pump HEX-CAP holding in the Plunger Spring… the (7) Torx T-30 Gerotor Oil Pump-to-Front Timing Cover Machine Screws MUST be unwound and the Outer Pump-Cover-Assembly MUST be removed FIRST. The reason for this is because there is a LEDGE Cast into the Lower Horizontal Flange of the Aluminum Front Timing Cover-Gerotor-Oil-Pump Assembly designed in as a “Last Ditch” effort to keep the HEX-CAP from completely coming off of its Screw Mount over the Coiled Spring should it become loose. It IS possible to insert the 5/16” Hex Wrench Socket into the Hex Hollow of the Aluminum Screw Cap... but as the the Cap is being Unwound Counter-Clockwise… that small Cast Aluminum “Ledge” WILL Break Off that Piece of the Lower Aluminum Flange.
(7) The Gerotor Oil Pump is capable of Pumping 11 + Gallons of Motor Oil Per Minute during its normal operation.
(8) The Oil Pressure Relief Valve is designed to use its Plunger or Piston to squeeze down against the Strong Spring just enough to allow the Over-Pressurized Motor Oil to By-Pass the Main Oil Pick Up Chamber and return the Oil to the Incoming side of the Oil Pump. This happens automatically and even though the Plunger-Piston is in the constant presence of the lubrication offered by the Engine Oil… if Sand, Grit or Metal Particles get Vacuumed into the incoming Oil Stream...Those Gritty Particles CAN get JAMMED in between the Steel Plunger-Piston and the Aluminum Bore and cause the Plunger to cant sideways and get JAMMED AND STUCK INSIDE of the Bore.
(9) If this Stuck Open Oil Pressure Relief Valve event lasts for even a small amount of time, a Catastrophic Drop In Oil Pressure can put the Engine Cylinder Walls, Pistons, Rings, Crankshaft and Connecting Rod Bearings at risk of Seizing Up. IT IS VERY IMPORTANT TO REALIZE THAT THE OIL GETTING VACUUMED UP FROM THE LOWER CRANKCASE AND FLOWING IMMEDIATELY INTO THE GEROTOR OIL PUMP IS UNFILTERED.
(10) It will NOT be Possible to Remove the High Grade Steel Plunger-Piston through the Upper Threaded Bore in the Base of the Gerotor Oil Pump as that component is TRAPPED below the Thread Lines for the HEX-CAP. However, It WILL be possible to use a Pencil Magnet to Check the Piston for Freedom of Movement gliding in and out in that Chamber. But If that Piston is found to be JAMMED solidly inside the Body of the Gerotor Oil Pump… REPLACING THE GEROTOR OIL PUMP & TIMING COVER CASE AS A COMBO-UNIT: GM Part # 126 28565 should be considered. An Alternative choice is to keep the Timing Cover Case and ONLY replace the Gerotor Oil Pump using the Sealed Power Kit Part # 22453582 which includes the Inner Gerotor Dual Gear Set, The Outer Pump Cover, the (7) 10.9 Hard T-30 Torx Fasteners and the all important Oil Pump to Engine Block Black Rubber Grommet-Seal. Before Installing the Dual Gerotor Gear Set into the Front Timing Cover Inner Cavity... Soak them both down in Motor Oil.
The Gerotor Oil Pump Autopsy Images can be seen as linked below via my “Flickr-Bucket”:
https://www.flickr.com/photos/126111508@N07/albums/72157713216978312/with/49571444046/
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