1996 3.1 oil pressure problem

[Gearnut]

Hi, I'm a engine builder with 30 yrs experience but I can't quite put
my finger on this. A dealership down the street has a 1996 Grand am
3.1 with a rod knock. Engine was quiet except the rod would sound-off
if you reved it. Their mechanic (Joe) pulled the engine, put in a reground
crank and new rod and main bearings and 1 reconditioned rod. He only
had 1 head off the engine. Following this, the lifters are noisy and they have never quieted down.

They put in new lifters, no change. (would have been my guess)

The gage on the dash shows 60 psi and varies with rpms so we are
"assuming" the oil pressure is good. I told them to do a live test which they
will do... but for now I'm just passing on what info I know. I was there when
he had the dist drive out and spun the drive shaft and oil was pouring
out of the hole in the block indicating the pump is for sure working.

My question is, if he installed the earlier main bearings, would it block oil to the
top of the engine ? He never had the cam out. There is zero oil flowing out
of the push rods. I tried finding a oil circuit diagram for the engine but
am unsucessful.

I know Joe did NOT mic the crank
so he could have a undersize crank (happened to me once), and there
are a number of other possibilities... but I am wondering about these main
bearings.

Clevite shows a main bearing change starting in 1990 they went to MS-1897 P, before that it was MS-1631 P and I remember something about the holes being different... just a hunch if he had the wrong mains in the engine could that block oil flow .

Thanks in advance for any help, you can also contact me at gearhead4you@yahoo.com Mark

[bszopi]

Maybe these will help....

[Gearnut]

Ok thanks. I can see it can't be a main brg problem with the exception of too much clearance causing low oil pressure. I told them to do a live test. Thanks for the cutaways. Mark

[PCGUY112887]

60psi at what, idle? I only get 35psi with my 3500...

[bszopi]

My engine is usually between 45-60psi at idle (02 3400).

[geoffinbc]

I'm betting on a blocked lifter galley or severely restricted one. The oil flow on a 3X00 motor is just just like a small block. The center main above the cam feeds the cam bearings which sit in a seat with an annular groove around it. This groove allows oil to flow around the back of the cam bearing where a vertical hole just below the cam bearing feeds oil down to the crank.

There is 2 more main oil galleries on either side of the center gallery which feeds the lifters, the lifters in turn send oil up through the pushrod. Restricted oil to one or both of these galleries will cause lifter tick and lack of top end oiling.

[cleanz]

You wouldn't by chance have the cutaway for the 2.8 ?
Thanks

[bszopi]

Unfortunately no. Sorry... Someone else might have access to it though, as you can usually find the cutaways like above in the Factory Service Manuals.

[cleanz]

Thanks.
I'll try the dealer tomorrow.

[geoffinbc]

The older engines are the same in most respects. The only difference being the left gallery above the cam does 2 jobs. It feeds the lifters and the cam and then oil passes around the cam bearings and down to the crank just the same as the 3X00 motors or a smallblock. The Gen I and II motors use the same oiling as the 4.3L V6.

[Gearnut]

Thanks for all your help guys. It was a "hung" oil pressure relief valve. Turns out the oil pressure was less than 15 psi at 2000 + rpms when they did a live test. The mechanic assured me the oil pressure gauge on the dash was showing 60 psi and varied with idle, but he had the intake manifold off when I first seen the car so there was no way for me to verify it. He may have a defective gauge or sending unit also the way it sounds.

Once again, I appreciate your input.

Mark