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Roger, welcome to the forums!  Happy to jump into your oil priming issue...


Most remove the distributor and prime the oil pump with a drive key or appropriate tool and a drill motor.  The reason is clear:  Simply priming or filling the oil pump with oil will only create faster pickup of oil at the pump; this will not "prime" the lubrication system. 


If you do remove the distributor and spin the oil pump with the oil pan in place and motor oil in the pan, the pump will pick up prime then flow this oil into the lubrication system via the oil filter stand, the oil filter and the oil passageways within the engine.


There is an alternative; however, it's more costly and typically used by shops that do a lot of engine work.  This solution is an oil priming tank.  You place a suitable amount of oil into the clean tank, pressurize the tank with compressed air, and flow the oil into an engine block oil gallery plug hole.  If you select the right gallery plug for priming, the oil will charge the lifters, reach the cylinder head, crankshaft bearings and camshaft bearings, even flowing backward toward the filter and pump.  The idea is to have all lines charged for the initial engine startup, leaving no dry or lube-less areas in the oiling system. 


Note: Here is a Melling oil priming tank and more details: http://www.melling.c...e/Pre-Lube-Tank.  I have a tank like this, purchased from Goodson Tools several years ago, and have used it on conventional engine rebuilds, vintage engine restorations and performance engine builds. 


I would take the time to drive the oil pump through the distributor drive opening.  To begin, rotate the crankshaft in its normal direction of rotation and bring it just to TDC on the compression stroke.  Remove the distributor cap and note the rotor position carefully.  Mark the rotor's position in relationship to the distributor housing. 


Note: I use yellow auto parts marker and place this mark at the distributor housing's cap seat.  The mark should be centered with the rotor's tip and easy to identify later.


The distributor housing base has an indexing slot, but to be careful, mark a line at the distributor housing base and engine block.  Once the distributor housing to block position is marked, you can remove the distributor.  Do not rotate the crankshaft with the distributor removed.  You can install the distributor in the correct position later, with the rotor tip in correct alignment with the housing.


Now, you can drive the oil pump (crankcase filled to normal level with fresh oil), using an appropriate pump drive tool and drill motor.  I like to use a 1/2" heavier duty drill for this job, one that can center over the distributor hole in the block.  Carefully drive the oil pump.  If the pump pickup screen is properly positioned in the oil pan, the oil should pick up quickly.  If possible, use a slow drill speed for this task to prevent galling the pump gears during the oil pickup phase.


Caution:  Always make sure the lifters, pushrods and rocker arms are in position before charging/priming the oiling system.  Otherwise, the lifters can overfill and extend the lifter plungers too far.


Tip:  For those having difficulty finding an AMC/Jeep oil priming drive tool, consider this option:  Fabricate a tool from an old 4.0L distributor.  Remove the distributor's drive gear and the accessible electronic parts.  Use the old distributor's housing to keep the shaft on center with the oil pump drive.  (Clean all parts thoroughly before inserting them in your engine!)  The distributor shaft—with the drive gear removed—can be driven by a variable speed 1/2" drill motor.  Attach the drill where the rotor would normally fit.  Oil the shaft as necessary during the priming operation.  Carefully keep the drill on center with the distributor shaft .  (Again, the drive gear must be removed from the distributor shaft!)  Keep the shaft engaged with the oil pump drive to prevent damaging the oil pump drive.  Use a slow drill speed to help keep parts aligned.


Once oil is flowing through the pump and system (oil filter must be in place), you will hear the drill load increase.  It's helpful to place an oil pressure gauge on the system to monitor the oil pressure, or use the factory oil pressure gauge at the dash.


Warning: Do not crank the engine when activating the dash oil pressure gauge!  Carefully turn the key to just the 'On' position.  Avoid the 'Start/Cranking' position!  As the drill motor charges the oiling system, the oil pressure can be read on the dash gauge by a second person.


When oil has sufficiently charged the system, the crankshaft and camshaft/lifter areas will have oil.  You can now install the distributor, using the rotor position to determine which drive teeth of the camshaft to engage.  Again, do not rotate the crankshaft during this process.  If the oil pump will not engage with the distributor's pump drive, simply pull the distributor out of the way and rotate the oil pump shaft slightly.  Try again until the distributor drops back into its original housing position with the rotor aligned.  Make sure the distributor housing indexes with the engine block and seats properly.


If you haven't disturbed the position of the crankshaft and camshaft, you should be right back in original distributor timing.  The 4.0L distributor (used through 1999 engines before coil-on-plug) does not have a provision for "adjusting the timing".  Once in proper position, the distributor housing should not be moved. 


Note: On the 1991-up MPI Jeep 4.0L inline sixes, you do not "set" base timing like older engines with a conventional ignition.  Crankshaft at TDC on the compression stroke, simply align the rotor/distributor shaft properly with the distributor housing.  If the distributor housing is indexed correctly with the engine block, and if the rotor indexes correctly with the housing, spark timing will be referenced from the crankshaft position sensor (CPS) and controlled by the PCM (fuel and spark management computer).


Trust this raises your confidence level and inspires oil priming the engine correctly...



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I had a pretty bad rear mail seal leak and the engine oil pressure was on the low side. Decided to replace the oil pump at the same time. biggest chore was getting the pan off and back on, it was a very tight fit between the bell housing and front differential. I put the rig on jackstands, disconnected the shocks and let the axle sag as far as possible.


The install of the oil pump was very easy, would have been better to pull the distributor first (it was tricky lining up the oil pump drive with the dist. shaft). I followed Moses' instructions using a 1/2 cordless drill and an old screwdriver (removed the wooden handle, cleaned it up on a wire wheel and ground three flat spots to help the chuck grip the shaft). It was a little trickey keeping it centered in the dist. drive hole so using a modified dist shaft assembly would definitely be easier.


I spun the pump for about a minute (slowly at first) until it primed, and ran it for another 30 seconds or so (there was a surprising amount of resistance once the pump started moving oil).


The rear main seal went in easily, took my time and used quite a bit of liquid soap to lube the top half. Like I said the toughest part for me was getting that oil pan back in place and aligning the new pan gasket.


The old oil press was 40 psi at start up, dropped to 15 psi when warm at idle, now it's about 50 at start up and just below 40 at idle. I've only put 50 miles on it, but so far the new seal is dry.


I've never participated in a forum like this before, I'm looking forward to learning a lot.





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You accomplished a lot here, Roger!  Your home built oil priming "tool" worked nicely and is a great example of ingenuity around using inexpensive, on hand resources. 


Working beneath the vehicle with the pan down is always a challenge.  Raising the chassis and using stands on the frame to allow maximum axle sag was useful.  We're fortunate with these beam axle vehicles; trucks with IFS or even Ford Twin-Traction Beam models have chassis that can be difficult to work around.  Rolling new crankshaft bearings into a 300 inline Ford six (Twin-Traction Beam F150 4x4) and installing a new oil pump and pickup screen—in the vehicle—was a complex job.  The cross member support for TTB made pan clearance very tight.  I loosened the motor mounts and raised the engine, as much as the body, transmission and transfer case would allow, to get the pan out and perform this work.


The one piece oil pan gasket on your Jeep 4.0L inline six is a huge asset.  "In the day", I worked with a fleet of inline six GM, Ford and I-H trucks that had four-piece oil pan gaskets.  In-chassis work with the pan down meant juggling all four gaskets and keeping them in place during pan installation.  Side rail gaskets (sometimes even the end gaskets!) were cork, which required tying the rail gaskets to the pan bolt holes with thread.  (Once aligned, with pan bolts started, you could cut the thread loose before compressing the gaskets.)  A breakthrough at the time, stiffer, composition side rail aftermarket gaskets from Felpro and Victor made this easier.  The four-piece gasket arrangement plagued inline and V-engines for many years.


Modern, one-piece "rubber" pan gasket solutions were a major breakthrough for both inline and V-engines.  These gaskets have also proven tough enough for reuse in a trail emergency repair; replacement is recommended during service work. 


Congrats!  Good project, great outcome...Thanks for sharing your approach with others, this is valuable...Looking forward to your involvement at the forums!



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