JDODD

So i have an 87 jeep cherokee XJ 4.0L 6 CYL. and i was replacing the Oil pan seal and removed the oil pump to do so ( i dont have a lift)...and now i put it all together and am looking for a way to prime it i tryed while it was out.. i put the pick up tubein a container of new oil and spun the shaft on top with a electric screwdriver and well nothing happen maybe i have a crappy screw driver... i do know of the other ways to prime the engine just not sure of whats the best and how to properly do it .. the screw driver method down the distributor or disableing the ignition system and turning over the engine.. i even heard of filling the oil filter then quickly turning it over and screwing it on and trying to start the engine...just i dunno if that would work. so my questions is clearly whats the best way to prime an oil pump ( already in the jeep) and how to do so clearly.

Cherockee

I've always used the method of pulling the distributor (make sure your timing marks are lined up first), and I made a tool from a large, very long bolt. I attach it to a 1/2" drill and spin the pump up until it gets pretty stiff. Then reinstall the distributor correctly and you're on your way.

I'm sure in your case you can just pull the coil wire and crank it over until you get pressure would be fine. The above method is usually used when overhauling an engine.

cruiser54

Pull the coil wire. Crank it til you see pressure. That won't take long. Reinstall the coil wire.

kjc

Can't del a msg.. Well i'll try again.. Since I don't know how an oil pump works. May I suggest you kill the fuel pump as opposed to the ignition while cranking your engine to prime your oil pump..? My thoughts are that pumping raw fuel into your cylinders while you crank your engine to prime your oil pump would cause some unwanted friction. A little spark plug firing would do less harm i think. C'mon fellas, what do you think?

kjc

As I understand it, the reason for priming the pump is because it will not pump air.. at all. All the spinning in the world won't prime it whether it's in the engine or not. You have to fill it with oil, then install it. This according to the instructions I got with the rebuild kit. You can pull the distributor and spin it with a screwdriver or something, but i'm afraid that won't work w/o oil already in the pump itself. You said you spun it with a screwdriver on a drill and that it didn't pump. I think you're going to have to pull the pan off, take it out and fill it with oil. I'd get a rebuild kit. They aren't too expensive and it's well worth it for your peace of mind.

Bustedback

Packing the oil pump gears with grease or vasoline will help it prime.

cruiser54

I have never primed an oil pump on a 4.0 and all I did was crank with the coil wire disconnected til I saw oil pressure (less than 30 seconds) and then hooked the coil wire back up. Simple. It works.

cdf43

X2
I just did the oil pump on my 87 XJ I just disconnected the coil and turned the key for about 30 seconds. Hooked the coil back up and started it

cruiser54

It ain't much different than right after you change your oil. When the oil pan is empty, all the oil in the pump drains out through the pickup screen. Think about it.

cdf43

That's not entirely true. When you disconnect the pump a lot more comes out. So when you put a new pump in its dry and you have to prime it so you don't damage the pump and engine components

cruiser54

It doesn't get damaged in 20 seconds at 300 RPM cranking speed. It has assembly/machining lube in it anyway. So do the original bearings have oil on them. The same oil they would have from shutting the engine down anytime. And, a new engine would have assembly lube on the bearings for that specific purpose, to protect the bearings until the oil pressure appeared in about 20 seconds.

I've done this way too many times on many different types of motors and I know it works just fine.

And, if the oil doesn't drain out of the oil pump after an oil change, how come it takes a few seconds to build oil pressure upon start-up afterwards.

SeriousOffroad

any engine builder worth his salt will tell you the same thing;
1) pack the pump with vasoline
2) pull the dizzy and use a drill and rod with a flat to prime the entire system. A got 60-120 seconds will ensure your galleys are all full.
3) if your motor doesn't fire...STOP. Fix the problem and don't keep cranking the engine.

rrich

SOME drains out on an oil change. But there's enough left to help it get started pumping again.

Best way - when it's out, pack it with Vaseline.

But now - cranking or starting it with 0 oil pressure - it doesn't really hurt the pump much, but the cam really suffers!
Sure you can try it, but at what price?

cruiser54

Guys: We're talking about an oil pump replacement, not a new engine. All the bearings will be fine. The cam is broken in. Crank til there's pressure on the gauge. Hook up the coil wire.

SeriousOffroad

Removing the pump allows the oil in the galleys to drain out, this doesn't happen when performing a basic oil change.

A little extra effort can prevent damage to bearings and the rotating assembly.

Seems like a simple preventative step to take.