chevy oil pump main stud, install info

[grumpyvette]

ok Ive got to point out that the use of a studs much better than a BOLT,because their use results in a stronger mount , and youve got much better control on the depth the threaded tip has on the rear main bearing , you install it by cleaning the threads with a thread die to verify they are correct and running a tap thru the main cap threads BEFORE installing the main cap, (COURSE THREADS ON THE STUD GO INTO THE REAR MAIN CAP) then after torqueing the REAR main cap in place , lightly coat the stud threads with LOCTITE, running it into the main cap threads until it touches the back of the rear main cap bearing then back it off about 1/2 turn, so it doesn,t touch the crank bearing shell... ONE FULL TURN max.
you then install the pump, place the hardened washer and tighten the oil pump nut on the stud.
(THE OIL PUMP MOUNT STUD MUST NOT EXTEND THRU THE MAIN CAP ENOUGH TO BEAR ON THE REAR OF THE BEARING SHELL)
MORE USEFUL INFO

BE 100% SURE that the oil pump bolt or STUD doesn,t protrude past the inner main cap surface , because if it bears on the rear main bearing shell it will almost always result in a quickly failed rear bearing

failure to use the correct stud, bolt or nut or check clearances when mounting an oil pump can cause problems

ONE RATHER COMMON MISTAKE IS USING THE WRONG OIL PUMP STUD OR BOLT TO MOUNT THE OIL PUMP AS IF EITHER EXTENDS THRU THE REAR MAIN CAP IT CAN AND WILL BIND ON THE BEARING AND LOCK OR RESTRICT, SMOOTH ROTATION

BE 100% SURE that the oil pump bolt or STUD doesn,t protrude past the inner main cap surface , because if it bears on the rear main bearing shell, it will distort the surface and it will almost always result in a quickly failed rear bearing

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it won,t hurt to check the pumps end gear clearances, remove any casting flash or crud and coat the gears with assembly lube, and braze the pumps pick-up tube to the pump body ater carefully verifying the pick-up to oil pan floor clearance is between 3/8"-1/2" (don,t forget to remove the bypass spring and piston temporarily, then replace them)
coating the gears with a decent assembly lube allows the pump to prime faster

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[grumpyvette]

question comes up, can you replace the oil pump while
the engine remains in the corvette,

Ive replaced BOTH oil pumps alone and oil pumps and oil pans several times, on c4 corvettes, both L98 and LT1s while the engine was still in the car and on the motor mounts,its fairly easy to pull the pan and replace the oil pump on a C-4,place the car on a level concrete surface and on 4 jack stands one on all four corners at about a 18"-22" height so you can work under the car safely,
the diagonal braces to the k frame usually need to be temp removed and the coolant lines under the oil pan disconnected, the starter usually needs to come off, but generally the only trick is the crank needs to be rotated slowly once the oil pans free to allow the counter weights on the crank to clear the front lip on the pan because you can only lower it slightly due to the cross member. make damn sure the oil pump pickup is 1/2"-3/8" off the oil pan floor once its installed and BRAZED or welded or bolted in place on the pump
now what does quite frequently happen is that the guys installing a high volume oil pump just swap out the standard pump, reinstall the stock or similar pick-up and bolt on the pan with the pick-up in the stock position on the oil pump. the stock pick-up is mounted about 3/8" off the pan bottom,the high volume pump is normally equipped with impeller gears about .3 inches longer than stock, the high volume pump body is that much lower in the pan, resulting in the pick-up being only about 1/8" from the pan bottom. the result is that on a normal Chevy oil pump pick-up this leave a space of about 1/8" x 2.5" for oil to flow into the pump. at low rpms this works but as the rpms climb the pick-up that can,t get any oil to pump gets into cavitation as it spins and fails to pump oil, result oil pressure drops until rpms are lowered no matter how much oil is over the pick-up. simply checking to make sure that about 1/2" of space is under the pick-up when the pan is installed cures that problem (a simple trick is to weld a 1/2" thick nut to the oil pump Pick-up base and test fitting the pan BEFORE WELDING OR PREFERABLY BRAZING THE PICK-UP TO THE PUMP BODY)theirs two ways , lets go the cheaper route,you clamp the oil pump body minus the gears and base plate (which you remove temporarily) in a vise with the tube entrance facing vertically and clamped between two sections of 1/2" plywood to cushion the vice jaws you find a crows foot open end wrench that slides over the oil pump pick-up tube but not over the ridge, in the tube that in theory prevents you from inserting the tube too deeply into the pump body.
use a 8" extension and the crows foot wrench and a rubber mallet to seat the pick-up tube into the pump body, then temporarily mount the oil pump and place a lump of modeling clay on the pick-up body lower surface and install the oil pan for a second to compress the clay giving you the distance between the oil pump pick-up and the oil pan floor, adjust it until the distance is approximately 3/8"-1/2"
once that distance is correct BRAZE the pickup to the pump body AFTER temporarily removing the bye-pass spring so it won,t get annealed
once that's done you clean lube and re-install the pump components and verify clearances, and the gears spin freely with out binding, don,y forget to use some MOLY assembly lube on the gears to assure it primes quickly
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[grumpyvette]

if you want more PRESSURE sooner you need a HIGH VOLUME PUMP WITH THE LARGER GEARS since the larger gears sweep more oil per revolution they build pressure faster, NOT MORE PRESSURE, JUST the SAME PRESSURE EARLIER at a LOWER RPM LEVEL, AND they PEAK OUT at what ever the BYE-PASS circuit spring pressure is when the CIRCUIT OPENS, and stops the increasing rpms from building FURTHER PRESSURE increases

Z-28/LT1 SB Chevy Oil Pump
Part # 12555884
Production high-pressure Z-28/LT-1 oil pump with 1.20" gears.

SB Chevy High Volume Oil Pump
Price: $64.97
Part # 14044872
This high-volume pump has 1.50" long gears. It has approximately 25%
more capacity over a production pump at standard pressure


look the difference is gear size, both pumps potentially make the same PEAK pressure ,if the same bye-pass spring is used... but the high volume pump reaches that peak pressure at about 80% of the RPMs NECESSARY for the standard pump to reach that same pressure because its sweep volume due to smaller gears is about 25% less so it requires about 20% more rpms to pump the same volume of oil to reach the same pressure

IF you use a stud to mount the oil pump, make sure you use loctite on the course threads and only spin the stud into the main cap until it barely touches the rear main bearing shell then back it out about 1/2 turn so there's no extra pressure & stress exerted on that rear main bearing or the main cap,the result will vary with the force exerted on the back of the bearing shell, if the force is MINIMAL, (as in the stud just touches but there's no compressive force on the bearing shell) nothing will happen that will effect performance, HOWEVER if there's significant force bearing on the rear bearing surface it will distort the bearing surface and disrupt the oil film supporting the rear main journal ans slightly distort the concentric radius of the bearing, adding drag loads(FRICTION) to the crank rotation, and lowering the load tolerance, potentially resulting in bearing failure, that can and does on occasion cause other problems, so be aware and prevent the problem .