Can bad lifter(s) cause low oil pressure?

I wouldn't say it is shot. I would do one of two things. Put a set of main bearing in it if you have the limited fund for doing so, or do what my Dad did for all those years and just make sure your oil is changed right at 3000 miles and run that GTX 20W50 or the straight sae 30 weight and a can of motor medic, STP or the like.

I am serious when I am telling you that Dad pulled the camper and did not baby that engine after the oil pressure dipped out. He put the title for the truck in the glove box and always said she'll either go or blow and his plan was if it blew up from lack of oil pressure he was going to have it towed into a dealership and let them take it for whatever he could get in trade on a new one... hahaha

But I even drove that truck with the weak oil pressure and I drove the dog piss out of her. Dad's mehanic buddy told him that while it certainly wasn't ideal but the engine would keep running as long as he held between 5-10 pounds at highway speed he said of course more would be better but said that it only take that 5-10 psi to get the oil to the top of the engine to keep everything coated.

The only thing I ever seen Dad do to give that engine a bit of a repreve was when he was pulling the camper and it was hot outside (most of the time he pulled the camper was hot out) he would put it in Nuetral or park when sitting at a traffic light or sitting in heavy traffic and keep his foot on the accelerator just a little bit to keep the pressure in the 2-5 psi range while at idle.

Cripe with all the new additives and such out there today I would even put a bottle of SLICK 50 in there just for a little more insurance.

 

I say tear the engine down and find out what is wrong. Might be a easy fix?
Just my two cents.

 

This got me thinking...I remember back in the mid 70's a friend had a low oil pressure problem. He found the pickup tube very loose on the oil pump. Loose enough to suck air. Would this be considered an easy fix?

Maybe...maybe not. Would a bad oil filter's bypass valve cause this?

 

That got me to thinking, too. Mine used to be the same way, it only held about 5-10 psi hot idling. I knew mine was a high mileage engine, but sometime in it's life it has been built, so I wasn't really concerned. I figured I'd run it a while to get the bugs out of the car then rebuild it.
I started out with a FRAM filter. At that time, you couldn't find a Motorcraft filter in my area. Don't know why, but nobody had them. I bought some NOS Motorcraft filters from Dan Hines at FFW that year in Atlanta. Didn't change the oil until the next spring, only had 2000 miles or so on it all year. When I changed the oil, I used 20w40 Pennzoil, 1 quart of Lucas, and a Motorcraft filter.
No more low oil pressure. Even just before I changed it this year, another 2000-3000 miles on the oil, it still held 20-25 psi at idle.
Long story, yes, but a bad filter will drop oil pressure.

 

Especially Fram junk. I just replace the main and rod bearings in mine, total cost for bearings was around $60.

 

Cheap fix: drop the oil pan, remove the rod caps a journal at a time and repl the rod brgs, remove the timing cover and trans and lower the crank about 1/2", slide new main brgs in and see what it does. It will cost you the gaskets and bearings. I did that for a friend on a budget and it lasted another few years. You can inspect the bottom end stuff while you're there, so you might find the root cause in the process. rthomas has a point with the bypass valve and the loose pickup.

 

I've replaced main bearings without removing the trans and TC cover. You will need to remove the main cap and loosen the others to drop the crank thousands of an inch. Insert cotter pin in the crank's oil hole and turn engine backwards with a socket. The pin will roll the bearing out. To install, reverse procedure. Then torque the mains to spec.
Side note: Never use sealer on the oil pump or pickup tube...use motor oil instead.

 

Is there a chance this could be just a rod bearing? Can one rod bearing cause a big drop in oil pressure?

I'm hearing rod, main and cam bearings from people. Of these, the only ones I looked at when I put this thing together were the cam bearings and they looked just fine. I know that they have to be measured to really know, but I would think I should see some of the plating eaten off if they were loose enough to cause this kind of a pressure drop, right? Overall, I don't think the whole engine is worn out. The bores looked great, there's no smoke...

If I drop the pan, look at the main caps one by one and I don't see visual evidence of wear, then replace at least the one, or maybe all of the rod bearings, (assuming I don't see visible crank damage) is that a reasonable approach or am I dreaming?

 

if a rod bearing is bad enough to cause that drastic of pressure loss, i would expect that you could move the rod end on crank journal. so you should be able to drop the pan and try wiggling each rod end to see if you find a loose one. dont forget the oil pump may be loose or its pick up tube could be also. it does sound like you need to pull the oil pan to make your next decision.

 

I was hoping to hear something like that.

I'm pretty confident in the oil pump and pickup tube. That was the first thing I did before I started this thread; replaced the oil pump.

Now, how will I know whether the crank has been machined? If the block's been bored .060" I have to assume this engine's been rebuilt twice. Maybe not, but let's assume... That to me increases the chance that the crank has been turned. There are different size rod bearings, right? Are they marked?

 

The crank should be marked

 

The bearings are stamped with the over/under amount on the back. (the side that is against the cap)

 

May want to do oil sample! It`ll show bad bearings. Ask a big truck shop if anyone local does samples or Black stone will do it through the mail.

 

Could be somebody used the wrong size bearings.....standard on a .030 under or something like that. You really need to mike the crank to be sure of what you have. I don't know if the parts houses rent mikes out or not, maybe you could borrow one if you don't have one....

 

I didn't pull all of the bearings, just enough to know what I'm up against. That's four rod bearings from the first two journals, and the #3 and #4 main caps.

Looks like I'll be replacing all of the rods and mains, since everything I've pulled so far is showing copper. The cam bearings did not look like this, at least not when I installed the cam.

How do I decide whether the crank is usable? Or does this picture pretty much say it's not?