I have a 85 351W From a F-150 pick-up which I have recently rebuilt.
During cam break in I had a drop in oil pressure from 40 to 20 psi half way through break in, it then even got to about 15psi I shut it down, I wasn't sure if it was the gauge or something else.
I changed the oil and filter the oil was pretty dark but didn't have anything really noticeable as damage.
After I'd changed the oil I also added another gauge to double check the one I was using I then reprimed the oil pump with my drill, it went to 40psi both gauges after running engine after about 5 minutes oil pressure started to drop again.
My engine has a Comp Cams camshaft with flat tappet lifters which are also Comp Cams I initially used Joe Gibbs break in oil which has the ZDDP additive in it, second time I used 5w30 with Lucas Oil ZDDP additive, can any body help me out? Thanks

 

I have been told it could be a cam bearing, can any body agree with this; could it be the oil pump please let me know.
thanks

 

What exactly did your "rebuild" include?

 

I see 3 possibilities:

1. broken Sensor -> maybe the pressure is fine

2. Oil Pump worn -> maybe the pump hold pressure as long as the oil is cold

3. Oil to thin -> Try a ?w40, ?w50 or ?w60 ans see if the gauge changes

 

My rebuild of my 85 351w included having rotating assembly balanced, cylinders bored .030 over, resize connecting rods, hot tank block and install cam bearings and polish crank which were all done by a machinist also had new hypereutectic.030 pistons on to rods.
Comp Cams Xtreme 4x4 35-239-3 cam, Comp Cams High Energy lifters, Comp Cams High Energy alum roller rockers 1.6 and Comp Cams Hi-Tech push rods.
I also used Edelbrock E-street heads 5023 the ones with 1.90 intake valves, Edelbrock accudrive geardrive , Edelbrock victor series water pump also Edelbrock performer intake manifold.
The oil pump I believe is a melling, the distributer is a Pro Form HEI, I used Comp Cams Assembly lube on valve train components, I used Red Line assembly lube on main bearings, rod bearings cylinder walls rings and pistons.
I would appreciate any advice or input Im to the point of pulling engine to investigate which is not a big deal the front clip is off so a few hours it could be on a stand if needed.
Thanks Mike

 

If you do get into the engine, I would check the clearance in the main and rod bearing journals with plastigage.

 

Could be oil pump failue or a spun bearing.Either way,you'll likely be pulling the engine.That's the only way to find the problem and correct it.As beanscoot said check the measurements of the journals and the clearances.Also check the torque specs before you disassemble.

 

is that a standard volume pump or hi volume pump?

your using oil that is to thin. for engine break in for the first 3000 miles you should use delo or rotella 15w40, this will help the rings seat properly and gets all the crap out with each oil change. its a hi detergent oil.

 

I decided today I am going to pull the engine, you guys are right I will check clearances and torques again, when I get it done again I will use a thicker oil I still need to finish cam break in, I wasn't planning on running the engine with the thinner oil I was hoping I clean something out by just priming, without spinning anything; but when I had the pressure back to 40 psi I got excited hoping it fixed itself, you guys have been there right!!
Thanks for your help, Mike

 

By the way, I'm sure It is a standard oil pump It is what came with the engine rebuild kit

 

With a proper rebuild, a standard oil pump and regular grade oil (i.e. manufacturer's recommended) will be fine.

A high volume pump is suitable to compensate for a worn engine or a rebuild with excessive bearing clearances.