Unusual Oil Problem, need advice!!!

[Monziac]

I just rebuilt my 68 383 motor with a basic re-ring kit.  STD on both rods and mains and used the stock oil pump.  Clearances were .003 on all bearings.  I packed the oil pump with vaseline and tried to prime it (yes I spun it CCW).  The motor would not prime no matter what I tried.  I finally hooked up a vacuum pump to the oil sending unit port and got the pump to prime, I thought all is good!  I started the motor and I had 15lbs - 20lbs pressure hot which I also saw as good.  Reved oil pressure was 25lbs which I was not happy with.  I figured the regulator spring was weak so I pulled it out and put in a stiffer one.  I started the motor and had zero oil pressure.  I pulled the distributor and tried to prime the motor and again it will not prime?  What is causing this to lose its prime?  Is this a common problem with these pumps that is solved by installing a high volume melling pump?  Anyone have any advice? 

Thanks,
Jon

[BSB67]

Nothing jumps out to me as an obvious problem.  Check:
1) that you have oil in the motor
2) The gauge is correct
3) Filter is okay ( just change it)
4) There is a oil gallery plug in the front of the motor that is occasionally overlooked or forgotten, but this usually results in only zero pressure.
5) Pick-up problem (cracked/loose)
6) Bearing problem.

It is possible that it is a stack-up of problems, bearing clearances, lifter clearances, wore out oil pump.  Are they full groove mains?

[Monziac]

Yes, everything is new accept for the oil pump. 5 qts in the motor, pick up is new, bearings are new etc. Only reused part was the oil pump. As a matter of fact I left the housing on the block when hot tanked and only pulled the pump gears and shaft. I am very used to this style of pump as its similar to my old Buicks. I am dumfounded by the lack of oil prime.

Thanks,
Jon

[c00nhunterjoe]

I would replace filter and install a new pump, if no change then pull pan and check pickup.

[BSB67]

As a matter of fact I left the housing on the block when hot tanked and only pulled the pump gears and shaft.
Jon

How do you even do that.  You cannot take out the rotors without removing all of the bolts that hold the housing to the block  Did you then re-install three of the bolts to keep the housing from falling out?

I don't think you responded to half of the items I mentioned.

You seem to think that because something is new, it is not the problem.  New std bearing will not have 0.003" clearance.  And, again, are they full grove?

Just do what c00nhunterjoe said.

[Monziac]

I know "new" doesn't mean it can't be the problem, believe me I have replaced a lot if new items in the past. When I removed all the bolts the thrust plate came off but the housing stayed in the block. I tapped it with a hammer and it wouldn't come out so I left it in. I measured everything before assembly and paid attention to oil plugs. As for full groove they were standard bearings and yes it measured out to .003 on everything +- a thousand. I guess I will order a new oil pump and filter and see if it cures what ails me.


Thanks,
Jon

[fy469rtse]

you don't need to remove all the bolts to get pump off ,
put it back together and just take the bolts that hold it in to engine , 4 x off
hard soft mallet , not a steel one
gasket is holding it , with all the bolts out you can tap it so it turns breaking the seal of the gasket and o ring on shaft, 

[Monziac]

Thank you for that tip. I will tackle it tomorrow.

Thanks,
Jon

[Monziac]

So a new oil pump solved the priming issue. It must have been sucking air somewhere. It primed quickly but the guage read 20lbs so I replaced the gauge and it read 70lbs cold. I reassembled and everything is fine. New gauge on order. Thanks!