oil pressure drops from 50 to 0 when warm.

Yep, I think you have a spun bearing. Happened to me. Same symptoms.
 
You said you had a knock at some point - I don't like to hear that. OEM specs are pretty liberal, oil lights come on @ as low as 6lbs, they suggest 10lbs @ 1000rpm, 20lbs @ 2000rpm etc. I don't like to see oil press any lower that 25lbs at hot idle. And never a knock. And with your oil guage swingin' around like a tach I still think you have a bearing problem. Maybe drop the pan and pull the pump to have a look, maybe change it, they're cheap, fill it up with 20-50 and a new filter of course. Get it hot and see what happens.
 
No I have not heard a knock. That is what has me stumped. The motor runs smooth. It is a solid lifter motor with sidepipes so it is loud but when you put your ear near the motor you don't hear anything abnormal.

Thanks
Wade
 
If I have to tear down the engine what type of machine work would I need to have done. Keep in mind that this is a 500 mile motor now with what was a new SCAT crank, resized rods, new pistons.

Polish\turn crank?
Anything need to be done to the rods?
Block?
Rings still ok to re use?
 
So many different opinions I am sooooooo confused........ Several people on the Chevytalk forum have mentioned that GM spec for a BB at idle is #8. If I am running 20-25 at idle now with the conventional oil and I am not hearing any knocking or grinding I can't decide what to do, pull the motor or drive the thing.

If my clearences are on the loose side then they have been all along. One thing I have learned is to stop making wholesale changes and instead do one at a time. At this point I realy don't remember where my OP was pre adapter issue and RP synthetic. I can tell you that synthetic oil will not be going back in this motor ever. I am sure that there are a lot of fans out there that would disagree but I have found a wealth of info supporting what I saw with synthetic oil dropping OP dramatically on old technology engines and parts. I will stick to dead dino.......


I am going to drive the car around a lot this weekend. If OP stays consistent I am going to make myself stop starring at the guage. If it drops into single digits again then the motor is coming out.
 
Wade, hit a parts house for the stethoscope if you don't have one, you can't hear shit over a loud exhaust may as well converse with your chick under the end of the runways with 747's taking off.....

gotta listen to that block, and the valve covers, and whatEVER to hear any knocking.....

:clobbered:
 
Just a thought--

What lifters are you using? GM has 2 different styles- one is what I'd call a full flow- the oil hole in the lifter is in the groove around the center of the lifter body and the other one has the oil hole just above it, called "edge orfice". It only picks up oil when the lifter is all the way down in the bore.
 
TimAT said:
Just a thought--

What lifters are you using? GM has 2 different styles- one is what I'd call a full flow- the oil hole in the lifter is in the groove around the center of the lifter body and the other one has the oil hole just above it, called "edge orfice". It only picks up oil when the lifter is all the way down in the bore.
Click to expand...

Tim,

They are isky solid lifters with an oil hole on the face.

I took the car for a 1 hour drive today. OP was 5 constant at cruise and 20-25 constant at idle. I wish it were higher but at least it isn't 0. I think the plan is just to drive it and see what happens. Come winter time pull it out and rebuild the bottom end.

Wade
 
mrvette said:
This brings back mammories of my '61 Catalina with a full 'race' engine in it....built super loose, enough clearances to rattle ....

I held it together for some 60k miles on the street....at one point I ran two cans of STP goo in there.....

so the inevitable happened of course, got interested in some chick, forgot about the car....and obviously some damn cold front came through...went to zero or below for a week solid....I was walking, the starter could NOT budge that engine.....I even tried lighting a fire under the oil pan...serious....

life was crazy 40+ years ago, and ain't no better NOW, come think of it....

:eek::devil::surrender:
Click to expand...

Damn. Shoulda drained the pan, fired it and poured it back in while it was running.

Not that that's unsafe or anything. :sos::devil:
 
After it was resting in the garage for a few weeks I finally got the 79 out and had a little fun yesterday.... this thread got me curious so I paid a little more attention than usual to my oil pressure gauge.

Melling HV pump (55HV ??) and 10W-40 Mobil clean 5000 mineral oil:

oil cold, idle 1000rpm: >50psi
oil cold cruise... 2500rpm: 70psi

oil hot - idle 1000rpm 25psi
oil hot cruise 2500 rpm: roughly 50psi

When the engine is hot and my idle speed drops below 1000rpm to around 750/800 rpm the oil pressure drops to 10psi.

Yesterday afternoon I adjusted my cold idle to 1100rpm so hot idle is around 900.... btw, I have a manual trans...

Do you have a auto trans and is your idle speed 750/800 rpm ???
 
Same thing happened to mine, not as soon after the build but a few years later (about 60k miles) I drove it like that for two years (another 40k miles) and raced it quite often...

It was just fine, until the other day...

Now I have a bottom-end knock and am awaiting my new short block so I can get back on the road...:suicide:
 
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