I just finished putting the engine (5.4) back into my truck (1997 F-150 4X4 supercab) after new bearings, rings, pistons, valve guide seals etc. All clearances checked o.k. although one cam tower which I had welded and re-machined due to scoring was at the wear limit. I did not install a new oil pump. Oil pressure was fine prior to the re-build. Everything seems quiet and smooth but at normal operating temperature the oil pressure at 1500rpm is only 30 psi and it drops to 10 psi at idle. Before I start removing the engine (not much fun) and tearing it apart (no fun, but not as miserable as removing) does anyone have any ideas ?
If anyone is contemplating removing the engine from a similar truck I have a few words of advice that will facilitate the job if they want to ask.

 

Dirty, clogged or leaking pick up tube/screen. Faluty, oil pressure sender. Did you check pressure with a proper guage?

JMC

 

I cleaned the pick-up tube before I re-assembled the engine and used a new o-ring on the tube to pump body connection. I used a liquid filled 0-100 psi pressure gauge on the oil pressure sender port to measure the oil pressure.

 

Ring might need to seat. pump might need to be replaced. How about running the pump man. and see what pressure you get with the engine not running.

 

I'm not sure what ring it is to which you are referring. The oil pressure was o.k. before the tear down so I'm guessing that the pump is ok, although my first step will probably be to replace it if the pressure relief valve proves not to be sticking. The pump is a gyrotor style pump which runs off the nose of the crank so it would take a lot of work to make up a jig to bench test it. I apologize if I look like I'm shooting down everbody's ideas. I do appreciate the input.

 

Low oil pressure is often associated with crankshaft bearing clearance.
I know you did not want to read that but that is the best I can come up with.

 

I mic'd all the main and rod journals and I plastigaged every assembly when I was putting the thing to-gether (mains, rods, cam towers). With the exception of the one repaired cam tower which came in at the wear limit (.005 clearance) everthing came in basically nominal within a few tenths. I was wondering if any one can think of any small plug that I might have left out of the block or if there is any history of leakage between the pump body and block or the cam chain adjusters and the block ?

 

What does the oil pressure read when the engine is cold? If the oil pressure is near normal when the engine is cold, then I doubt that a oil passage plug is missing. With the oil pressure problem your having is usually caused by internal oil leakage due to excessive bearing clearances & or worn pump gears/housing. Did you have the block hot tanked & all the oil passages cleaned? Did you pack the oil pump with petrolem gelly before start up? Starting a new engine dry can destroy the new bearings before the oil pump can pickup the oil. Contaminates in the oil passages can do the same thing. Your probally going to have to drop the oil pan & look at a few rod & main bearings to see if there is any damage to them or the crank. I'd also plastic gauge them again as well. Good Luck!

 

I haven't checked the oil pressure cold. Thanks. I'll try that. I primed the oil pump with 90 weight gear oil and the pressure came up on the instrument panel gauge very quickly on first start-up. I changed the oil and filter after the first 15 minutes of running. I cut the oil filter apart and found only a couple of small smears of assembly lube and one almost microscopic sliver of steel so it looks like the engine survived initial start-up in good shape. I did have the block hot tanked, bored and decked by a reputable engine builder. Maybe I should have had him do the assembly.

 

I have never heard of reusing an oil pump after a rebuild? Just cheap insurance IMO. Hope it works out for you.,,,,98

 

In retrospect it does seem like it would have been a good idea to install a new oil pump. At least the quality of this component would not be a consideration in my current circumstances. Its starting to look like the old girl may get a new pump anyway. Thankfully the pump can be replaced without pulling the engine, although I'm tempted to do it anyway since its easier to a good job with the unit bolted to an engine stand rather than nestled in the engine bay.