A while back I tore down my rebuilt 390 because of a misfiring and tapping noise. Also the oil pressure dropped really low. I checked everything. The cam and lifters were in great shape. The rod bearings were good. A couple had light scoring from some junk that bypassed the filter but nothing you could feel with your fingernail. The bores looked fine with no grooves. The low oil pressure ended up being from a clogged oil filter. Tapping noise I think was from misadjusted lifters.

Engine is back in the truck. I added adjustable roller rockers, a new harmonic damper, and a new fan/clutch in place of the fixed fan. I put a holley jet in the rocker hole. My oil pressure is now 80psi cold at 3000rpm. Hot oil pressure is around 50psi at 2000rpm and 35psi around 1500 and 20psi or so at idle. After setting lifter preload the valve noise went away.

Now my newest problems are:

-Engine has a vibration that goes with rpm. I took off the belts and the vibration was much better.

-Engine started to go above 220 and I shut it down. I put a spacer to move the fan clutch closer to the radiator and it fixed it.

-Drivers side exhaust is burning oil fairly bad. Maybe an intake leak? The valve cover was leaking and running down too. Could it get pulled in to the exhaust if it's not completely tight?


Compression 1-8

1-158
2-155
3-155
4-160
5-145
6-160
7-160
8-155

Cylinders 4 and 8 had visible oil on top of the piston.

All spark plugs looked the same. They were all black and sooty. Which is to be expected cause until the choke comes off my AFR gauge reads 10:1 then goes to 13:1 when it warms up. Initial timing is 10 degrees.


Any suggestions would be helpful. Thanks.

 

Oil filters don't just plug, it takes an OMG amount of something in a new engine to plug a filter. that alone is a hair on fire red flag.

What plugged the filter ? nothing else matters until you figure that out. I would be amazed if you weren't having problems.

 

It was like a thick sludge. I still had like 5psi at 800rpm and more if it revved up. I dont know why. There's no oil in the coolant. I also decked the heads since last time and put new head gaskets.

 

It has been my experience that that FE motors will fluctuate oil pressures. If it drops below 15psi then I would be worried. Don't trust the factory gauge or sender to be accurate. If the oil light comes on then be worried.

 

Oil outside of the motor 98% of the time is coming from the valve covers and good luck sealing them.

 

There shouldn't be any sludge in a new engine that's strange enough, but what's real important is was the sludge metallic ? if so you are not out of the woods you have a problem that you missed.

As far as the other problems go,

was the rotating assembly balanced ?

It's possible if you decked the block and milled the heads the angle on your intake and the angle on your heads aren't matching and it could pull in oil around the port. not as likely if this was the only time it had been done but if it's the 2nd or 3rd time it's possible.

What condition are the guides in and what seals do you have ? most likely this is where your oil is getting in.

 

I think it was water from when it rained. It didn't seem metallic. The engine was not balanced but like I said the vibration seems to go away when the belts are removed. The valve seals are new but the guides are old. The block was not decked but the heads were.

 

Unless you're sure the engine had never been worked on you'd have to measure it to know for sure what all has been done to it. but if your guides are worn that's very likely where your oil burning is coming from not the intake gasket. new seals can only do so much.

If you're sure the belts are driving your vibration then it's probably either a bearing going out of something or a fan or something out of balance. unless it's bad I'd worry about that after everything else is taken care of.

You should check your timing curve to make sure it's in line.

 

I did plastigage everything when it was rebuilt and took measurements

 

Then you should know your deck height and cc's and that will give you an indication of whether it's been machined enough to be an issue. I've only had to mill one intake before but it can happen.

The guides are it most likely and they'll only get worse. depending on that type of seals you put on some help a little more than others.