No Oil Pressure on Newly Rebuilt 304

[jdcxyz]

Hi everyone, have a problem that I could use some advice on. Little background on this, it's my first engine rebuild. Did months and months of research before I ever started this project. Had machine work done by a reputable shop, magnaflux, line hone, block decked, heads rebuilt, had the whole thing balanced. Many new parts on this thing, no expense was spared. I was absolutely meticulous when I built this thing. Plastigauged everything and all was within tolerance. Filled her up with fluids, pulled the dizzy and primed with a drill and an old dizzy shaft. Oil pressure switch turned my electric fuel pump on so I thought the pressure was good. No real deflection on OP gauge, I thought maybe not enough RPM on my drill. Put the dizzy back in and turned the key. Literally started right up before the rotating assembly had completed one revolution I think. Sounded great even though I hadn't set timing. Ran smooth. Looked at OP gauge and it read zero. Turned it off immediately. Setup at the time was an electric sending unit for OP. Grabbed an old mechanical gauge and hooked it up. Got as much air out of the line as I could. Started it up, zero pressure. Turned it right off. Pulled the line of the back of the gauge, pulled the dizzy again and tried priming with my drill while observing the disconnected line from the OP gauge. A few drops dribbled out, that's it. I expected it to squirt out.

I packed the oil pump with Vaseline like I've read in numerous places. Plastigage clearance on the pump gears to pump body was good. pump spins smoothly. AND it is a brand new oil pump.

I'm at a loss. Is there something easy that I'm missing? I really don't want to pull this motor out and start again! Help!!

Thanks for any suggestions!

 

[Lumpy Grits]

IF you really had no OP, the engine would have made all kinds of noise.
I would try another OP sender and gauge.
Hope this is an OEM ele gauge deal.
LG

 

[jdcxyz]

IF you really had no OP, the engine would have made all kinds of noise.
I would try another OP sender and gauge.
Hope this is an OEM ele gauge deal.
LG

Thanks Lumpy, I would have thought so too, but I used a TON of assembly lube and the motor only ran for about 15 seconds each time. I would have expected more than a few drops of oil from the mech gauge's oil line when I was manually spinning the pump.

It was an OEM gauge from quadratech. When the gauge didn't work, I hooked the contact to an ohmmeter and watch the resistance to ground (which is my understanding of how they work, a resisted ground to the gauge) and did not observe and change when manually spinning the pump. Guess I'll try a new one! Here's a picture of the sending unit

 

[RiverandSand]

I have never been a fan of packing the oil pump with anything(Except oil)! I think what your are seeing is a plugged oil passage to your sending unit. The Vaseline has created a blockage. I think you can remove the oil filter adapter on the AMC 304 which is also has your oil pressure port to clean it out.
No oil pressure as LG mentioned would have made big racket because the lifters wouldn't have pumped up. One way to verify pressure is to pull a valve cover, start it, oil should be runnig if not shooting out of the rockers.
Worst case if no pressure after checking the above is a galley plug is missing somewhere in the system.

 

[Lumpy Grits]

On the plugged passages.
I always used a light coat of grease and thick motor oil to prime the AMC V-8 oil pump.

Get one of these mechanical deals.......
Oil Pressure Gauge. Black Dial, Mechanical Oil Pressure Gauge.

Teflon tape on the sending unit treads messes with the GND, and can lead to the gauge not reading 'rite'.

LG

 

[JeeperChris]

15 seconds really isn't that long, that's why we use so much assembly lube on the cam/lifters, rockers and mains journals. That vaseline is probably still making it's way up the tube.

 

[Lumpy Grits]

IF there truly was 0 oil psi.
The lifters would not have built up pressure to work.
The engine ran-The lifters were working.
LG

 

[jdcxyz]

Thanks for the responses everyone, next step is to take a valve cover off and check for oil on the rockers. I also heard from a local AMC guy that there are two journal plugs in the lifter valley, that if removed will cause very low oil pressure.

Wrenching this weekend!

 

[Lumpy Grits]

PlZ keep us posted.
Good luck.......
LG

 

[yleefox]

I'm going to take a stab in the dark here. Assuming that you did not fill the oil filter with oil prior to installing it, I'd be curious if it was now full of oil. If it is, that oil had to get pumped there from the oil pan.

 

[jdcxyz]

Well it seems I may have found the problem. After removing a valve cover to discover bone dry rockers, I decided to remove the intake. Lo and behold, two journal plugs missing in the lifter valley. After consulting my local AMC guy, he
is pretty certain that's the issue. There are two additional journal plugs on the back of the block that if too long, will block the oil passage, and if missing altogether, will result in oil squirting out of the back of the motor. I about 95% certain I didn't see holes in the rear of the block, so I'm keeping my fingers crossed that this will sort out the problem!

 

[Lumpy Grits]

PLZ keep us posted and good luck!
LG

 

[RiverandSand]

Well it seems I may have found the problem. After removing a valve cover to discover bone dry rockers, I decided to remove the intake. Lo and behold, two journal plugs missing in the lifter valley!

Did a machne shop install all the plugs? If so I would have a talk with them, to ensure they know they were missing. Also make sure they aren't just oil drain back holes. I would spin the oil pump with a drill to see if oil comes out of the open holes.

 

[Lumpy Grits]

LG

 

[jdcxyz]

Well case closed. Plugged the journal holes in the lifter valley, spun the pump and pressure jumped right up. Pulled a valve cover off and spun the pump and oil literally shot across my garage all over my Chevelle!! I'll definitely tell the machine shop about that. I'm just glad the problem wasn't that difficult and all it took were a few pipe plugs from O-Reilly's!

I appreciate everyone's advice!!!

 

[Lumpy Grits]

Would like to hear what psi you now see.
LG

 

[RiverandSand]

That's great to hear! Glad it was a relatively easy fix.

 

[jdcxyz]

I was getting about 45-50 while manually spinning the pump with an electric drill on highest speed. This was a mechanical gauge. Hope to go back to my electric sending unit and electric gauge.

 

[Lumpy Grits]

I trust a mechanical over any electric.
LG

 

[JeeperChris]

What he said!