Engine in question is newly rebuilt 368 Y-block (56 Lincoln). I just built up the engine and it overall it runs great, with the exception of nearly zero oil pressure at idle after it gets to operating temperature. Running 30w oil, at cold start-up oil pressure will go to 50-60 psi. Upon reaching operating temperature I will get 0-5 psi at idle 750 RPM. (At 1250 RPM it will go up to 10 PSI). General info and other things I have tried:



1 - I confirmed the pressure reading with 2 different direct read oil pressure gauges (not electric).



2 - Changed the oil pump, but no difference in behavior



3 - Verified crankshaft bearing clearances. I re-checked a rod and main and both came in at around .0026 . Service manual calls for acceptable tolerances of .0007 to .0036 so it appears bearing clearances are with range.



HELP I need:



1 - Could Cam bearing clearance be suspect? Would that potentially cause this?

2 - Only other major machine work that I had to be done was 2 cylinders needed to be sleeved. Could that have breeched an oil gallery? If so, I would assume that it would be sealed back up with the new sleeve.

3 - I do not believe the oil pump is sucking air, due to no oil pressure fluctuations or air in bubbles in the oil.



ANY help with ideas or past experiences would be greatly appreciated. This one has me stumped.



Rob

Rob, The very first thing that came to mind before I even finished reading your post was "Did you replace the can bearings?"

Obviously that's also the hardest to check. I would check everything else you can think of or others suggest first.

"The Master Cylinder"

Enjoying life at the beach in SOCAL

How was the oil pressure before it was rebuilt?


Lawrenceville, GA

The block was a certified Ford rebuilt short block still in the original crate when I got it from an old Lincoln friend last year. I think it was built back in the late 60's so it had been sitting in the crate for many many years. I tore it back down and built it up with heads I already had. I had the crank polished and 2 cylinder sleeves were required. The pistons, rods, and cam were all reused but I did have the cam bearings replaced. Unfortunately I did not get the exact specs noted on cam bearing clearances from the machine shop. My thinking is that if it was common to have cam bearing journals machined back when the short block was assembled, and the new cam bearings the machine shop put in were standard then there is a chance the clearance is far beyond limits. However, I am told that there is only one set of cam bearings available for that engine.

It sounds like you have a clooged oil passage.  Maybe the cam bearing were installed improperly.  Try this.  Pull the valve covers and the dizzy.  Use a drill to spin the oil pump and see if your getting oil at the top of the engine.  Spin the hell out of it and see if you can get the oil pressure up and the oil to flow. 

Let us know what happens and we can go from there.

Greg

It was common for the Ford rebuilders to grind the bearing journals down around .015" and use undersize cam bearings. This could easily be your problem.

You might be able to remove the fuel pump and check for vertical movement on the cam. .015" clearance should be obvious.

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

Oddly enough I'm having the identical problem with a 292. Complete rebuild and balanced. Oil pressure at initial startup was 60+. Now it starts cold at 40 but idles at 3-5 lbs when warm. Comes up nicely with rpm but just isn't right. I havn't had a chance to troubleshoot it as yet. Other than possible improperly installed cam bearings it was also suggested to check the rubber seal where the pickup tube goes into the oil pump. Seems they can suck air if the seal is bad. If I run across any other ideas I'll post them. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Yet another WAG: side clearance on the rods.  At least it is easily verifiable.  Also, I hope you are not using a Fram PH 8 A.  As of late, they are junk IMO.  Motorcraft, Wix, or Hastings are all preferable.

I was wondering (read hoping) that the problem could be in the oil filter pressure relief. Another thing to check. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

All - *PROGRESS*! Many many thanks for all of the posts and ideas. You guys are great. I spent the evening in the garage and the possible good news is I think I found the root cause. The bad news is that if I am right, then the root cause is my own stupid fault . As a test I decided to drive the oil pump with oil pan off and the engine inverted so I could see anything out of the ordinary. I rigged up a feed pipe to the oil pump from a jug of oil and had someone else drive the oil pump with the electric drill. **And yes ... I made an enormous mess** But, I found a large gush of oil coming through the hole in the block where the oil pump drive shaft connects to the oil pump. Definitely not correct! I removed the oil pump and found that I put the d@$? gasket on 180 degrees off. Stupid, I know. With it incorrectly installed 180 degrees off, it fits, but then there is no gasket material between the pressure port and hole in the block where the oil pump drive shaft connects with the oil pump. Hence, I lose most of the pressure right at the pressure port of the oil pump! I reversed the gasket, bolted the pump back on and I could tell a difference as soon as I tried to drive the oil pump with the drill. The drill labored much much more and no more oil coming from places it shouldn't. I am kicking myself, for being that stupid ... but I never stop learning from my mistakes.



I need to reassemble everything, put it back on my engine run stand and then crank it up again, but I am convinced that was the problem. The gap at the oil pump was not big enough to drop the oil pressure when cold, but when hot at idle it just dropped to nothing. *MoonShadow - Check your oil pump gasket.



I am unable to run it this weekend, but I will post back next weekend with the final results. Thanks again for all of the help and hopefully this post can be referenced by others and save them some time.