So I guess first I should say this is my first post here,but I have been using all of this great information on this site for quite a while. It's been very helpful with my latest truck. I recently purchased a very nice 85 f250 2x4 with a 300 and a 4 speed. I bought it to drive to work everyday, which it was great for until last night. I was on my way to work and noticed a odd noise. I was only about 2 miles from the house so i decided to go right back home. By the time I got home it was much worse. I took a quick video right when I pulled in. Here is the link to the video

1985 F250 knocking - YouTube

Before this happened I had installed a mechanical oil pressure gauge and I was getting 25ish at idle and 40 while at 2000 rpm. Now the oil pressure would always increase when you gave the engine some revs but right after you let off the gas from being reved it would increase by another 5-10 psi then slowly decrease back down to 25. While i was driving home it still had good pressure and was acting normal aside from the noise.

I would assume this means that either a main or rod bearing is on its last leg and its time for a rebuilt. However I figured I would see if anyone else who has more experience with these engines has ran into something different. No chance it has anything to do with the oil pickup or pump? I'm trying to be optimistic. From what I can tell the engine probably has 130K on it due to the shape of the rest of the truck is nearly like new. I was told it has 30K but I doubt that is the case.

If it is a bearing and it needs a rebuilt, have any of you found that rebuilding vs buying a reman is cheaper or better in the long run? I really like the truck and would like to keep it but I can't afford to spend a lot.

I appreciate any help
Thanks,
Shawn

 

Is it at all possible it could be the water pump going bad.

Get a piece of pipe, pvc, steel, copper.... Use it to listen around with. That would tell you which slot to pay attention to.

To me rebuild is always better than replace. You make it how you want it..

 

No way your truck has 30k miles with that much blow-by out of the oil breather. Mine is supposed to have 122k miles on it, and mine has a bit less blow by than yours, and I estimate my truck actually has 222k miles on it due to how worn the motor is and what kind of condition it was in before I got it. My oil pressure is almost identical to yours as well, idle fully warmed is about 20 and cold is 40 or so.

Also, you'll do good going to a junkyard and getting a factory style oil breather that hooks to the air cleaner. I have that exact same chrome one on my valve cover and it lets all the blow by out of the worn out motor, sucks into the heater and blows it in the cab, and leaves a fog behind the truck while it blows oil all over the motor. I modified mine to accept a piece of 3/8'' fuel hose and ran the hose to the air cleaner like a factory breather, and so far no problem.

Blow-by indicates your piston rings are worn out or cracked. I can hear a little bit of valve-train rattle when the motor is running too.

I have a lifter knocking in my motor, and yours sounds sort of like my lifter knocking, but yours has a raspy, uneven sound to it that mine doesn't have. Unbolt the fuel pump from the motor and make a block off plate and run the motor without the fuel pump and see if it quits. The other reason why I suspect the fuel pump is the location of the noise, around the #2 or 3 cylinder. That, and a lifter won't just start knocking like that out of the blue unless it was oil starved, and you've still got pressure.

It does NOT sound like a rod knock, which has a tick-tock-tick-tock rhythm to it. A lifter has a tick-tick-tick-tick rhythm.

Also, I've noticed that with my motor, the lifter knocking on the camshaft sort of has a hollow sound to it sort of like someone hitting a piece of metal pipe. It resonates. It's definitely something on your camshaft, being a lifter or the fuel pump.

The bottom end on a 300 is STRONG. The only problems I think you have are the worn out piston rings, a little bit of wear in your bearings causing the low oil pressure, and that knocking on the camshaft.

If it's not the fuel pump, I'd look at the water pump like was suggested.

 

Doesn't sound like a rod knock to me either. Sounds more like an air compressor with a bad head gasket. Pull the belts and run it to rule out anything external.


Just for reference, here's what a rod knock sounds like

 

You need to diagnose this, first.

I would take the valve cover off and see if anything looks amiss. One of the guys who used to be on this forum (CamoLaw) came to my house with a 6-banger with similar symptoms, turned out one of the pushrods had somehow freed itself from being contained between the lifter and rocker arm. That cylinder wasn't firing at all (obviously) and, being loose like that, made a noisy racket (don't remember about the blowby).

Here's a pic of the guy holding his bent pushrod:

 

Ok so I've been messing with it tonight. I first took off the fuel pump and blocked it off and ran it. Still making the same sound. Then I pulled the pushrod cover and all pushrod could be spun by hand. Then I pulled the belts off and tried that all still the same. I got me a piece of hose and listened all over. Sounds like it is coming from the rear of the oil pan and more so on the passengers side.

 

I listened a couple more times. I could swear it was clearest and loudest when you was by #1-#2 plug. Almost seemed in time with the puffs from your breather. I also heard it at the rear heater core side but back there it sounded more hollow.

Does it get louder or faster with rpm. For some reason it reminds me of a first boiling steam sound.

 

I should have said that but no it literally completely stops making the noise when the engine is revved up at all off idle. It has a very poppy sound to it.

 

Then it's a lifter.

It will tick like crazy at idle, but if you rev it up in neutral or park with no load the tick will go away because there isn't a load on that lifter and the lash gets taken up while it sort of "floats" in the lifter bore. Same thing with giving it gas when your driving. It'll tick like crazy and sound like it's going to blow up under load, but as soon as you get off the gas and take the load away, it'll go quiet.

You can pull each individual lifter and clean them/inspect them to see if you can re-use them or spot which one is bad, but I'd just replace the whole set. Get a quality set of lifters, don't get the cheap ones.

Usually, when a lifter goes bad, it's due to wear where the push rod sets in the cup just above the check valve in the lifter body, and it'll also wear on the body of the lifter where it rides on the cam lobe. Chances are, that lifter is probably dished on the surface that rides the cam, and if your motor is like mine, the rocker arms, push rods, and lifters are all pretty worn and should be replaced. While you're pulling them out, it would be a good idea to check the camshaft to make sure the cam lobe isn't worn down or damaged.

I went back and took another close listen at your video. Right when the tick happens, I hear slack being taken up in the valve train.

If you take a fancy to snake oils, you could try Marvel Mystery Oil.