I just got my new engine swap (1989 5.0 TPI with 20,000 miles rebuilt) running. I noticed something very distressing... The engine seems to be knocking. However, the sound COMPLETELY disappears if I open the oil cap or remove the passenger side PCV.

Oil pressure is about 40 psi idling at 700 rpm.
It has been making the sound since I first started it. Disconnecting spark advance has no effect.
Total run time, about 30 minutes, on and off since last week. Up until today I thought it was the severed A.I.R tubes making the noise, but I test capped them and the noise remained. I then opened the oil cap to see how much oil was making it to the rockers and the noise vanished...

HELP
Brendan

 

you do have a breather in the other cover dont you?

 

It actually looks like 2 pcv valves. One is connected to the lower intake under the plenum.(the driver side one) The passenger side one has a pcv valve in it and is connected (now) to the no vacuum port on the TB. I'll go check to see if the other is also a pcv valve.

 

no you have it right it looks like a pcv but it is just a vent should be on passanger valve cover at the back

 

It IS two pcd valves. It was like that when I got it, I assumed the passenger side was just a breather....
Can having two pcv valves installed cause that sound?
Did it damage anything?
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They are at the center of the valve covers.. I took them both off, and they are both pcv valves... I tried blowing through them to be sure.

 

sure could if you remove the oil cap and the noise stopped

 

I suppose that's true....
I really want to understand WHY the noise happened, and what i was. I understand that the crankcase pressure was all out of whack due to the lack of a breather.... I really just want to make sure that it didnt hurt anything.

 

The PCV valve in the breather side would have kept fresh air from entering the crankcase, so the PCV valve on the other side would have been putting the crankcase under vacuum. Opening the oil cap or removing the breather would have allowed air in to equalize the pressure.

 

i could tell you but it would only be a guess and it wouldnt be good... but for only 30 minutes i dont think it could have caused any damage

 

I think the pressure pulsations maybe were causing the oil pan to
"oil-drum" (sheet metal popping in and out). It shouldn't have hurt anything since the crankcase would have had negative pressure on it.
I had one engine we had built knock loud as hell when we put it back in only to find we had dented the pan very slightly and the crank counterweight was hitting it. It sounded like one rod had no bearings in it at all .

 

dont laugh but i had put valve covers on upside down on wrong side once and lifter hit covers ,they are taperd slightly on one side.

 

yeah those lifters shooting out of the bores are a menace...

 

I figured out what the noise was. It is the oil pan hitting the crank slightly. The vacuum forced the pan upward and made it more pronounced. It still does it sometimes... I crawled under and I can feel it hitting on the pan.

 

Damn, that sounds familiar...

 

, you called it!
I should have changed the pan while it was still easy!