Rod knock.

[CieraSL92]

My buddy has a 88 Ciera with the 2.8. It has 201k miles on it and has developed a deep, very deep knock. It is not coming from the top, it's slightly louder near the oil pan though. It seems to be concentrated to the center of the engine block. It always knocks, but is the loudest on light acceleration and deceleration. Oil pressure was checked and is 30 PSI hot idle.

He asked me how long he had left with it, and I said not very long at all. Am I right? The engine runs okay, and doesn't overheat. I did tell him that now would be the time to start babying it since one good dose of hard acceleration could end it's life.

How long in theory could you go with bad rod bearings?

[Burgundy Ciera]

Could die any second but could last up to a few months or so it's hard to say. But 201k miles on a 2.8 is a feat in iteslf.

[Slacker]

Just some perhaps interesting information I found while doing some research on rod knock...



Re: How many things "Sound" like a rod knock, but arn't!
Mechanical fuel pump, loose Harmonic balancer, loose torque converter and the aforementioned cracked flex plate have been some that I have experienced. Pull one plug wire at a time while its running, and if one cylinder has a knock, it will stop or change tone when you pull the plug on the effected cylinder. Good luck! - Mike


I'd say try pulling the plugs out to make sure it's the cylinder that's knocking.

[85_Ciera_Rebuild]

2.8. It has 201k miles...developed a deep, very deep knock.

How long in theory could you go with bad rod bearings?

Rod bearings do go out...but usually, your engine goes Kaput shortly.

>Oil pressure was checked and is 30 PSI hot idle.

That's decent Oil pressure....and within 2.8 specs for vehicle running about 30 mph (1500+ RPM).

I'd have to hear it knock...apparently, he's going to run it in the ground...if he could pull the pan, he could get to the bottom of it.

[CieraSL92]

Just an update, the engine siezed while he was in New Hampshire yesterday.

[notsoslimshady76]

that stinks. But I guess it had a good run right?

[CieraSL92]

Yeah it did. The trans had been shifting hard for the past year or so. So that would have probably gone soon anyway.

[85_Ciera_Rebuild]

Just an update, the engine siezed while he was in New Hampshire yesterday.

Bummer....he could have saved it....

[85_Ciera_Rebuild]

Oil pressure was checked and is 30 PSI hot idle.


His gauge must be off...my 2.8 has about 12 p.s.i at hot idle...until I change oil pump shortly.

That pressure is what you expect at some 30 to 45 mph, which is around 2,000 rpm at 45 mph or so.

[CieraSL92]

He actually only has a light for it; I used my guage. I kinda thought it might be off a little bit since it sometimes sticks (12-14 year old gauge) but I assumed it was a ballpark figure.

What's the factory spec? 12psi seems way too low.

[85_Ciera_Rebuild]

What's the factory spec? 12psi seems way too low.

Chilton Says: Engine 2.8 W - 50-65p.s.i.@2400

With 10-40 oil...somewhere around 40 ( I never really tested it at 2400)

OEM Oil Pump was set at 70 p.s.i....vehicle has electronic dash with bar-graph...but after checking electronic oil sensor via injecting shop air into it at 30 & 60 psi...this vehicle when cold does not hit 60 psi.

Currently, I have pulled the pan off tonight...removed the oil pump...and am thinking about putting in new standard sized Rods/Mains with new stock oil pump.

Motor has 150,000 miles on it...runs great with good fuel economy...no real oil burn detected after 1,000 miles driven...just a valve cover and crank seals needing replaced.

[LordDurock]

yea my B&G v twin 14hp does 40 hot and 65 cold :)

[85_Ciera_Rebuild]

What's the factory spec? 12psi seems way too low.

I know of another person who runs 14 psi at hot idle...which is somewhere around 600 RPM.


Btw, here's a tune for your friend: Queen-Another one bites the dust (http://www.youtube.com/watch?v=hMenB9Ywh2Q)

[85_Ciera_Rebuild]

What's the factory spec? 12psi seems way too low.

It's not an unusual pressure when your Oil Pump is By-Passing...

I pulled Rod/Main Caps...and they looked excellent for 150,000 mile motor...still has GM Rod/Main bearings.

So, later I checked the oil pump more in detail; pump gears/housing look fine....but when I used shop air set at 50 psi on pump's bypass circuit...it leak out air.

Btw, after checking some more sources...this I think is valid oil pressure hot:

Oil Pressure (Engine @ Normal Operating Temp)
30-55psi @ 2000rpm (205-38OkPa @
2000rpm)
(http://users.spec.net/home/emxjc/)

PS: Watch out on torque specs...for Rods/Mains...I've seen three different values listed for Mains torque...60...70...80 ft. lbs...on 2.8 W motor...GM Shop Manual says 80.