Alrighty guys, its been a while. To keep things relatively short im just going to get into it.
Roughly 1.6-2 months ago I had my freshly rebuilt 351W installed in my 1993 F250
This engine was sent to a machine shop in Tennessee over a year ago, where I lived at the time. But I no longer live anywhere near there. The gentleman who measure my block said I didn't need any machining work done. The block was 4.060 bore, .020 undersize rod bearings and main bearings. I can not remember what he said about the cam bearings, all I know is he said they were good and he left the original ones in. There was no visible damage by what I could tell. I had installed brand new rod bearings and main bearings.
I will give a detailed list of parts of anyone inquires about it. But I also installed a new Melling oil pump with both sump gaskets, and the blocks mating surface.
Skip ahead roughly a year I finally get this engine installed in my truck in my new location, Kansas. She starts up beautifully, no sounds, no aches or groans. But as she warms up she loses oil pressure. Cold she started at 59 psi. As she warmed up she kept dropping, fully warmed up she was at 12 psi at 1500-1600 psi, at idle she dropped to right near zero. I stopped the engine, and drained the oil. Was misty from the assembly lube, but no metal shavings (*yes I used break in oil), Next I had put in 10w30 shell rotella, off and on (I made sure that it never got to where oil pressure would affect the engine as stupid as that sounds), drained again, no metal shavings. Since then she has been docked.

Anybody who has any idea on what the cause could be, if you could comment down below. I would be very grateful. My brain is leaning towards a bad oil pump *even though it seemed to work fine when first primed*, or bad bearings/machine shoppist did not do his job properly.

 

Did you change your oil filter with your oil change?

Mechanical oil pressure gauge or electrical?

Did you check clearances on your bearings?

 

#1 yes
#2 first noticed the problem with electrical, installed mechanical after and same result
#3 No, this was my first rebuild and this is one of the things that were not done. I assumed that after the machine shop was done with it that it would be good to go? Also if there was to much clearance what would one have to do to fix it? Send it to the machine shop again?

 

The engine will not go much over .060 oversize
Same with the crank at .020
That is possibly why the machinist said it was okay (tolerable he should have said)
You had better either put a washer or 2 in the oil pump relief spring or install a HV pump
While you have the pan off, use plastigauge to check the bearing clearances
New to all this or not, you got to start somewhere, and this is it for you
The plastigauge is a must if you do not have a set of mikes and the where with all to use them
Possibly get some inside and outside micrometers and start to acquire the feel (used ones are cheap)

 

Good oil pressure when the engine is cold that drops when the engine is warm is a sign of excessive clearance in your main or cam bearings.
It could also be caused by forgetting to install (or falling out) lifter oil galley plugs behind the timing chain cover, but your hydraulic lifters will be noisy at cold-start if this was the case.

 

I'm sorry to say I have the same darn issue. I rebuilt my 351W over winter and installed it about a month ago. Ran like champ for about 500 miles then lost oil pressure on the dummy gauge. Installed a brass T fitting with a mechanical gauge with almost the same results as you, 45psi cold 5psi warm at idle. Possibly the new oil pump failed; I'm not sure the cause but main bearings are likely spun (excessive clearance). I'm in the process of pulling my engine to install a new crankshaft, AutoZone has them for $450, should be here in a couple days. Lucky for you KC is the Midwest hub so you might get it the same day. I really am sorry for your loss but happy to know I'm not the only one who didn't plastigauge the bearings before installing the engine. With it on the engine stand, this would've taken less than an hour but I was in a rush...

 

Well I appreciate all your guys thoughts on this. Been talking with my Grandpa and a coworker who used to rebuild engines. We all agree that there is probably to much clearance, however I already have a high volume oil pump on order. So my plans are to first use 20w50 (on a new motor, I know, my stomach turns just thinking about it). And see where the oil pressure ends up, it if it rises, it means its a clearance issue, if it doesnt, probably the oil pump. Which I will replace after the oil test. However if the oil pressure does rise to within acceptable levels, then I will probably just be forced to run it with how it is. I knew when building this engine that if it could even be rebuilt, that it would be its last life. As "manicmechanic007" said, .020 undersize bearings and 4.060 bore is the max that you would want to do. I will let you guys know what happends this weekend, but if it does work. I will probably get a plan together to build the original motor that was in my truck, that was all standard (the engine that has the oil pressure issue I bought from a gentleman in Tennessee due to the original 351w in the truck melting cylinder #3 because my foot got a little heavy, she had near 400,000 miles anyway, cylinder walls appear fine, but I will findout more as I tear into her).

Thank you guys.

 

Update: Put 20W50 in her, only raised oil pressure by about 3-4 psi. I went ahead and changed the pump. For the love of god, this was probably the most difficult thing I have ever had to do on this truck while it was still in the truck. Undid engine mounts, tranny crossmember, I had to push on the crank pulley with a 2x4 on jack, only to find a piece of railroad iron laying around to wedge where the engine mounts are to hold it up. Then blindly shuffling around trying to get a feel for where everything was. This was definitely not fun. But oil pressure definitely bumped up a notch. I didn't have a chance to drive her but when she was at operating temperature oil pressure was idling around 17ish, and when you press the gas she easily made 40. Will let you guys know what happens where he takers her on a drive.

 

That is exactly how you do it
I jack the motor up (using the harmonic damper) and use big sockets to hold it up
At the shop, on a hoist, you use a pole jack and quit cranking it up just as the truck starts to move on/ off the rack

 

Yeah, I remember doing the pump on my 5.8, not a fun job at all. Oil dripping on me the whole time and hoping that my wood shims didn't shift and have the engine come down on me. While you were in there, it might have been wise to replace the main bearings. Hopefully the new pump serves you well.