Lower Oil pressure

[83Blzr62]

On my newly built engine, I have had low oil pressure. It was at around 8 psi at idle untill I found out that I left the oil cooler bypass valve out. Now it idles at 12psi when warm and 40 psi when cold. Is there another plug I could have left out. I got the two for the lifter galleys, the two valves and plug under the oil filter, but is there any more?
I checked my bearing clearence before I built it and it was on the high side but still within the limits. Could it cause it to be this low?

[john8662]

Bearing clearance is pretty crucial.

Cam bearing clearance is probably really one of the more important yet usually unchecked things during the assembly.

re-using a cam isn't a bad thing, especially if it's a roller cam (like ours are). But, the bearing journal diameter should be checked and assured it's in spec even after the polish that the machine shop will do to verify it's size.

Oil pressure comparisons..

'86 6.2.

Rod clearance .002"
Main Clearance .003"
New Clevite Cam, spot on size.

Cold Oil Pressure 70Psi (fac gauge, verified close) 2k RPM
Cold Oil Pressure 60Psi Idle

Hot Oil Pressure 55Psi 2K RPM
Hot Oil Pressure 35Psi Idle

Stock Melling HS55 Oil Pump for a 6.2L


'95 6.5.

Rod clearance .002"
Main clearance .002"
Re-used cam on the low side (best out of the bunch I had)

Cold Oil Pressure 65Psi (fac gauge, verified close) 2k RPM
Cold Oil Pressure 60Psi Idle

Hot Oil Pressure 55Psi 2K RPM
Hot Oil Pressure 30si Idle

GM High-Volume Oil Pump for 97+ 6.5 in a non-oil spray block.


There are some obvious differences.

What I've figured out is that the Cam clearance is pretty important, since it was the only part of the equation that's not "tight" if i had to do it again I'd buy a new cam, with big journals again.

The difference that's also important here is that the 6.5 has the high-volume oil pump and the 6.2 doesn't, yet the 6.2 is making the better pressure.

And one more wrench for the works. A larger oil cooler (HB7) is on the 6.5, so that may contribute as well.

So, to answer the question, is 40Psi oil pressure directly related to having .004" bearing clearance? I'd venture to say that it may.

You're in spec though.

Good that you found the missing bypass valve (for the oil cooler). I'm sure glad that my machine shop always installs those ahead of time, so I don't forget.

J

[Robyn]

One thing to remember, the 6.2/6.5 family are what's known as top oilers.
The oil flows from the oil pump though the filter and then to the two oil galleries that feed the lifters and the cam journals.
There is a grove behind each cam bearing to direct the oil to the passage that drops to the mains.

From the mains which has the groove the oil flows through the passage in the cranks to the rods.

Unless you have a cross drilled crank which the 6.2/6.5's dont the rods get oiled while the oil passage is aligned with the top main groove only and while the passage is on the lower bearing shell the rods dont get oil.

Moot point for a low RPM engine but that the jist of it.

Loose cam = low oil pressure as has been said.
Another thing to be sure of is that your gauge is good. Hook up a manual gauge of known condition and check things.

Many GM dash gauges suck.

[More Power]

The oil flow schematic says oil flows from the oil pump to the oil cooler first, then from the oil cooler to the filter, then to the lifters/cam/mains/turbo.

I've only had two of these engines rebuilt, but the cams were re-used in both. Both had about 45-psi highway cruising speed oil pressure.

I've sorta changed my mind about engine machine shops and their use of equipment for polishing crankshaft journals or camshaft journals. Essentially, the equipment is a large belt sander equipped with a narrow (main bearing width) 400 grit belt. The dry belt will ride the journal as the crankshaft is being turned in a lathe. The light touch and skill of the operator affects the quality of the finish. As such... there is considerable opportunity to remove too much material and/or produce an out-of-round journal.

A Youtube search for crankshaft polishing will show you what I'm talking about.

Jim

[DieselDavy]

Jim,
I'm guessing you're looking into this because of your current project?
You didn't have to let them touch either the crank or the cam did you?
Dave

[More Power]

Jim,
I'm guessing you're looking into this because of your current project?
You didn't have to let them touch either the crank or the cam did you?
Dave

The crankshaft I'll be using was purchased from Jerry's Custom Engine, a local rebuild shop near me that had rebuilt a couple of engines for me in the past. The crankshaft had not been polished or reground. It was also very nearly brand new. The ultra fine factory crosshatching was still visible on the journals and the rear main seal surface had almost no wear. Dr. Lee (he visited us after the eclipse) and I looked at it very carefully, and pronounced it to be a genuine GM crankshaft, though neither of us could explain why it had so little wear.

We compared the crank to two others I have laying around. The cast parting lines, casting numbers and time stamp markings are all there and match the style and placement as those found on the GM cranks. Don't see how it could be a Chinese knock-off. I have seen a couple Chinese crankshafts, that could be easily identified as such.

The cam I have won't be ground, though it will likely get a quick polish here using 1000 grit wet/dry and WD-40.

[Robyn]

Sounds great.

Are you using new lifters ??


Is this 6.5 for the 2 door Tahoe ??

Spray block or earlier ??

Getting good oil pressure in the late spray blocks can be a challenge to say the least.

The AMG block I built for the Dahoooooley (Now with the Son in law) ended up with about 10-15 psi HOT IDLE

Road speed psi is about 35-45

I told the kid to bump up to the diesel rated 20-50 oil and that helped a bunch.

If I could do it over I would have plugged off the oil squirts to 1 2 3 4


The rear cyls are the hot ones.

Just way too many LEAKS in these engines.

Good luck on the build