I put LE2 heads and a custom grind on the motor, started it up and it ran fine. I drove the car for a day and noticed a slight knock from the passenger's side. I can't hear the knock from inside the car at all, or even from the driver's side outside the car. I can only hear the noise when the hood is up and when standing on the passenger's side. I've readjusted rockers, checked plugs, replaced header gasket, etc. and the noise is still there. Using a stethescope, the noise is pretty prominent if I hold it on the pan on the passenger's side, and it's pretty quiet on the driver's side of the pan. The knock goes up with RPMs if I rev the motor, and it doesn't seem to get louder or quieter...stays steady in volume.

The strange thing is, I can only hear the noise on the passenger's side. Even with the hood up, standing on the driver's side, I can't hear the noise. Maybe this is because it hasn't had a chance to progress, but all the spun bearings I've heard, you could hear from all sides, inside the car while driving, etc.

I tried disconnecting the plug wires on the passenger's side one at a time with no change in the sound. Is it normal to only hear a rod knock on one side of the motor? It would seem that since the bottom end is reciprocating that you would hear it on both sides. Next step is to pull the oil filter and look for metal shavings.

The bottom end is a forged Nutek 396 with ~ 1500 miles on it. I'm afraid it's a spun rod bearing, but wanted to get some opinions before pulling the motor.

 

^^^

 

change the oil and see if you can see anyhting? how is the oil pressure? sure the headers are ticking or tapping the k member? possibly post up a video so we can hear it if possible

 

The header is clearing the k-member and the oil pressure is 80 psi at cold start up and holds ~ 50 at idle once warmed up.

 

Pick up a mechanic's stethoscope and listen for it. If it's coming from the bottom of the oil pan then it may be what you think. Else, you could pin-point the noise to vavle train, exhuast leak, etc.

 

You might try reading the thread again. I used a stethoscope and the noise gets louder when I put the stethoscope on the pan. Also, I readjusted the rockers on the passenger's side and replaced the header gasket.

 

how old is your belt tensioner?????

I know it sounds funny but i thought my stock motor was toast till i got under the car and started looking around. I noticed the tensioner moving up and down. Easy way to tell is to take the belt off and see if it still makes the noise. Mine was starting to push the metal seal on the back of it out. It sounded just like a rod since it was clicking on the metal access. bracket.

Just something else to think about.

 

Was the cam ground on a small base circle ? If not, you could have a lobe hitting a rod. Depending on the lobe lift, it would need to be on a 1.050" or smaller base circle to clear most rods on a 3.875" stroke.

 

Any more ideas? The cam wasn't ground on a small base circle, but I don't think it needs to be for a 396 and .600" lift. Maybe Bret will chime in.

 

Well, I pulled the oil filter off today and cut it open. Not one trace of metal shavings. Is it possible/likely to spn a bearing and have no metal shavings in the oil? No metal shavings in the oil filter and 80 psi of oil pressure at anything above idle. I'm starting to wonder if the noise isn't a bearing.

 

If you're having bearing issues, it will show up in the filter.

Back to my previous post.... With a 3.875" stroke, the cam must be on a small base circle or rods will hit the cam.

If you've eliminated all sources of external noise, and the cam was the only internal part that was changed, it's reasonable to suspect the cam.

 

I would have to agree with the previous post, you need a .950" base circle cam (I am pretty sure that is the right size, could be wrong) to clearance the rods on the larger crank like the previous poster stated. Sorry to be bearer of bad news. You CAN clearance the rods to clear your cam, but this weakens the rods (not what you want to do).

 

Actually, I found what was causing the noise, and it wasn't the rods coming in contact with the cam.

http://web.camaross.com/forums/showthread.php?t=470534