Low oil pressure on rebuilt engine...help

[351YJ]

We were going to attempt to set the timing on the motor I just rebuilt. However, the oil pressure seems really low. We had the motor running at 1100-1200 rpms, but the psi was only 10-15. If we goosed the carb up to 2000rpm's it would only go up to 25psi. It doesn't go any higher than that. I'm not sure what's going on. Last weekend when we started it for the first time it was at 40psi, and it hasn't been there ever since. I replaced the oil pump today, but haven't had a chance to check it out yet, b/c I ran out of time. So it will have to wait til next weekend when I can get the pump primer. The pump I replaced was a Sealed Power pump. The "new" one is a Melling pump. I have a Melling pickup tube on it as well. I believe they are standard volume pumps. The oil pump driveshaft was new when I put the first pump in.

A mechanic-friend said it "could" be the main bearings, but we would hear the crank "slapping" around. We didn't hear anything like it.

I'm running a mechanical Autometer gauge. We also tried another gauge on it to see if that was the problem, but it gave us the same reading.

Specs: '79 351W, hydraulic cam/lifters, D00E heads, flat top pistons, Melling oil pump.

I'm really lost here, and need some help from you expert Ford guys.

 

[351YJ]

Forgot to add: The oil is Valvoline 20W-50 from the advice on this board, along w/ a Purolator filter.

Also, when I dropped the pan to change the oil pump, I noticed a few small chunks of dirt. I have no clue where they came from cuz the pan was clean when I put it on. Anyway, they're cleaned out. Do you think they somehow got in the pickup screen or old pump and caused it to read low?

Also, does my line for my oil press gauge have to be bled? I don't think it does, but I was told that I need to.

Sorry for so many questions.

 

[76Broncofromhell]

did you put the plugs in all the oil passages? Check that all of them are there, otherwise the pressure will be extremely low.

 

[74bronc]

Did you plastiguage the mains and rod bearings during assembly? If so, what was the clearance? did you replace cam bearings? I am leaning toward a missing oil gallery plug on this one.

 

[351YJ]

I didn't plastigage them. (I guess I should've)

The cam bearings are new.

The machine shop that did the block put the plugs in. Pretty sure they are all in there, but I'm not positive. Where are they all located? There are I believe 2 behind the timing cover...how bout the others?

Thanks guys.

 

[ABurns]

Sounds like main bearings to me. I did the same thing once, didn't check the mains, and had oil pressure exactly like you're describing. Also check the plug under the intake manifold at the back of the block.

 

[74bronc]

[quote author=351YJ link=board=5;threadid=16832;start=0#msg128218 date=1051541229]
I didn't plastigage them. (I guess I should've)

The cam bearings are new.

The machine shop that did the block put the plugs in. Pretty sure they are all in there, but I'm not positive. Where are they all located? There are I believe 2 behind the timing cover...how bout the others?

Thanks guys.
[/quote]

A little story... When I rebuilt my 351W, a very reputable machine shop, specializing in Ford Racing engines, bored my block .030 and gave me .020 pistons balanced, pressed on the rods and ready to go. Luckily, I do not trust everything the machine shop does, so I ALWAYS check every single clearance, just to make sure. It is very possible that they messed up the machining of the crank or gave you the wrong bearings. It does happen. One thing we know for sure, you should have a hell of alot more oil pressure than 25lbs on a brand new motor.

 

[351YJ]

The plug under the intake is there and good. I checked it out before I put the intake on.


If it was the main bearings, wouldn't we hear the crank?

 

[ABurns]

[quote author=351YJ link=board=5;threadid=16832;start=0#msg128273 date=1051556195]


If it was the main bearings, wouldn't we hear the crank?
[/quote]

Not always.... Did you get the crank reground, or did you use new bearings on an old crank?

Just checking the possiblities, been there done that with the results you're having.

 

[351YJ]

I did not get the crank reground. It looked to be in excellent shape, so I didn't bother.

I'm kicking myself right now for not looking what size the old main bearings were. :-

If it is the main bearings, do I have to drop the crank completely out to change them? That's gonna be a huge pain in the rear.

 

[74bronc]

[quote author=351YJ link=board=5;threadid=16832;start=0#msg128312 date=1051565028]
I did not get the crank reground. It looked to be in excellent shape, so I didn't bother.

I'm kicking myself right now for not looking what size the old main bearings were. :-

If it is the main bearings, do I have to drop the crank completely out to change them? That's gonna be a huge pain in the rear.
[/quote]

So what size mains did you put in there? STD? I wonder if its been ground in the past and you put standards back in it. Keep us posted. I am interested in finding out what you find the problem to be.

 

[351YJ]

So what size mains did you put in there? STD? I wonder if its been ground in the past and you put standards back in it. Keep us posted. I am interested in finding out what you find the problem to be.

That's kinda what I'm thinking. I'm also wondering if it was reground in the past. I put STD bearings in it, and now I'm p.o.'d b/c I forgot to look at the originals. There is a decent possibility that is was reground. But would .010" of bearing clearance really make that much difference? I'm just curious.

Thanks for your help so far.

Is there anyway to drop the crank easily to replace the bearings or am I gonna basically have to pull my engine again?

 

[Lttrbox]

Is there anyway to drop the crank easily to replace the bearings or am I gonna basically have to
pull my engine again?

Ive done it once in my previous life. Lookin under my Bronco, I think you could drop the pan. loosen
up the mains and then go one at a time. Just need to make sure you dont force the orientation tabs the
wrong way. It seems you cant loosen the mains up too much or all those bearings will be a b*#$h
to align all at the same time. Dont know, I think Id pull it and avoid creating some other problem.

 

[351YJ]

That's true, plus my engine is in a Heep so I actually have a ton of open space under there. It's kinda nice. I might be able to do it that way. That would be a ton easier than having to move the tranny back or pull the engine out so the crank will drop out. Thanks for the idea man, that helps a lot.

 

[351YJ]

One question I just thought of: When a shop regrinds a crank, do they make all the journals the same size so I can use the same size bearings in all the mains? Or do they just resize one and leave the rest alone?

 

[74bronc]

[quote author=351YJ link=board=5;threadid=16832;start=0#msg128463 date=1051584787]
One question I just thought of: When a shop regrinds a crank, do they make all the journals the same size so I can use the same size bearings in all the mains? Or do they just resize one and leave the rest alone?
[/quote]

All machine shops I have ever dealt with will grind all the journals the same in order to avoid problems finding bearings. I have seen some cranks with the rods ground .010 and the mains .020 or vice versa.

And yes, if the crank is ground .010 and you put STD bearings in it, it will most definitely affect oil pressure. My bearing clearances were all .003 or less when I did my 351W, just to give you an idea. The oil pump is trying to pump oil into too big of spaces, hence the low oil pressure. I would bet this is your problem. If it is, it could be worse. You should be able to put the right bearings in it and go to town with no permanent damage.

You could do it with the engine in place. Might be kind of a pain, but might be easier than pulling the whole engine out again.

Good luck with this and let us know how it turns out.

 

[351YJ]

Thanks a ton, 74Bronc. You've been a huge help. I'll let you know how it turns out after I get to work on it this wknd.

If anyone else has any ideas, let me know.

Thanks

 

[Broncobowsher]

When I did my 351 I took the (bad?) advice from several sources. They said to run a loose bottom end. I set the mains to .0027" instead of the .0015". That little difference was enough to kill oil pressure. The HV pump and 15W50 it has good oil pressure mostly. It hasn't hurt the engine any that I can tell, nothing has degraded since the engine was new.

Again this was advice from several high performance engine builders. I also didn't just take the advice based on what they said. I though about it as well. The 351W has a big crank. those are 3" mains. The velocity of the jurnol against the bearing gets ugly at higher speeds. the bigger the jurnol, the higher the volocity for the same RPM.

Just think about this:
3" jurnol has just over 9" of curcumference. at 5000 RPM that is 45,000 inches the jurnol must slide across the bearing. (A 2" jurnol would only be 30,000 inches per minute) That's why I did my big clearences on the mains. The rods got standard clearances so they wouldn't "rattle around" on the crank.

Your performance engine builder may have given you a performance bottom end....

 

[351YJ]

Well, I didn't get to work on it much this wknd. All I had time to do was to prime the pump and crank the engine. After 15 seconds of cranking the psi only went to 10, it should be between 30 and 40.

I'm going to wait 2 more weeks til school is done so I can rip the motor out again and drop the crank out. Then I'm going to get the crank mic'd so I know what size bearings to use. Ugh...I'm trying not to think about it til then.

 

[j2hang]

just a simple question...Is the sending unit good / right for the application? It must be from a Bronco to match the guage.