Rebuilt Engine - black spark plug at #8

[bheston]

Hello,

I got my engine fully rebuilt and I have about 200 mile on it.  SBC 350 bored 0.030, alum heads, alum intake, Holley 650 vacuum secondary carb.  After about 50 miles, I changed the oil/filter.  I also put in new spark plugs.  I noticed #8 (right side rear plug) was black compared to the other plugs.  Even #6 looked darker than the others but not as dark as #8.  I thought I must have a bad plug wire.  Put on a new set of plug wires and new spark plugs.  Drove it another 50 miles and still #8 was black.  Checked the compression: 180psi in all cylinders including the suspect cylinder.  Put in a new Pertronix distributor thinking it might be the points.  No change.  Put in a new MSD distributor; no change.  I replaced the exhaust with a new one that I had been expecting to arrive for the last few weeks.  I drove around for a few hours today.  I noticed right away that my drivers side tailpipe is clean as new.  My passengers side tailpipe is sooty back (true dual, no x/h pipe).

I need the experts to give me some advice.  It seems to run fine.  No miss or hesitation.  If I wasn't watching the plugs/exhaust, I wouldn't know anything was odd.  I'm at a loss.  The engine builder has 30+ years experience with these engines.  He personally came to my house to see if he can spot the issues.  We found nothing.  He even drove it and could not detect an issue.

Do I have a valve adjustment issue?  Do I need to pull the head (gulp)?  Any advice would be much appreciated!


   

[bheston]

Exhaust pipes - Driver side clean, pass side looks sooty:

[ko-lek-tor]

#8 is using oil. Since compression is good and it is running well,  I would not suspect a blown head gasket. Oil can enter the combustion chamber 3 ways. 1) through the rings, 2) through the valves, 3)through a blown head gasket. Ruling out #3, either of the other 2 are possible. With only 250 miles, the engine may still be “breaking in” of the ring sealing. I would drive it more (few thousand miles)to fully break in the engine and for now, I would pull the spring off the intake valve of #8 (can be done on the engine in the car with care). I would grab that valve stem of the removed spring valve and see if it has excessive play. If movement can be felt, the guide is bad and the head will have to come off. If there are valve seals, other than the stock O ring, I would look for damage of the seal on that same intake valve stem or seal looseness on the guide, it may have popped off the top of the guide if it is the spring clamp Teflon type seal. While the valve cover is off, check head bolt torque and retorque as needed. Oil can also be introduced through the valve by a faulty intake gasket (check & retorque) and lastly, oil could be being sucked into the intake from an auto trans defective modulator valve and since #8 is the port that most vacuum is accessed, I would definitely rule that out and only if it is an automatic.

[RonA]

Oil also could be getting sucked in thru the rocker stud if there isn't sealer on the threads as the stud hole extends into the intake runner. If the manifold is not fitting the head 100% it can suck oil past the gasket.

[bheston]

I had a leakdown test performed on cylinder 8.  Getting 97% on the black plug cylinder - I think that is great for a engine still in the break-in period (maybe I'm wrong).  I tested #2 cylinder and I'm getting 96%.  Does that rule-out piston, rings, valves and head gasket?  Maybe bad valve seal is still a potential root cause?

[bheston]

The entire leak down test is complete:
Cylinder 1 - 3%
Cylinder 2 - 4%
Cylinder 3 - 4%
Cylinder 4 - 4%
Cylinder 5 - 2%
Cylinder 6 - 3%
Cylinder 7 - 3%
Cylinder 8 - 3%

Those numbers seem good. All leakage was coming from valve cover breather/pcv (crankcase). I did not hear anything in the exhaust or carb.

Oh, this is a 4-speed car.

#8 has the brake booster attached for vacuum. I wonder if a faulty brake booster check valve would cause issues? The brakes seem fine.

[Kelley W King]

While I agree with the above, a few thoughts. I assume you have a dual plane intake? Kind of makes the pics showing one side of the motor with darker plugs rule out a few things.  What heads? rebuilt original done at the same time? aftermarket? two that were not a pair? I think several valves on one side are leaking oil. I would start with all the seals on that side with the head on checking for excessive clearance while doing it. Worse case you can pull that head with the intake on. Just bolts, exhaust, ect. I frowned on doing that until we had a completely show detailed engine with a gasket leaking water in one cylinder. It was fairly easy and a little touch up on the head paint and ready to go. If you have an AC car I would drive it like it is.

[bheston]

Running a brand new ZZ4 GM Performance dual plane aluminum intake manifold 10185063.
Running brand new Trick Flow DHC 175 Aluminum Heads TFS-30210006.

I contacted Trick Flow and asked their opinion but I have not yet received a reply.  I was going to start by replacing the valve seals.  Out-of-box defects exists, but it *should* be less probable, right? 

Here is the engine FWIW.  I wanted the cast iron look:

[Kelley W King]

There is a utube video of a guy a guy checking out of the box aluminum heads mainly for valve angle cuts and leakage. It shows some really surprising things good and not so good. I think you brand was one of the brands. Valve seals would be my first place to look. I might would contact them and tell them you are doing that.

[z28z11]

If you are running a stock exhaust system, do you have the stock warm-up valve installed ? Operable ? Also, look closely at the oil drain passage at the end of the head, make sure you're not damming up oil around the valve when the engine is running. High volume pumps have a tendency to put a lot of oil where you don't really want it to accumulate.

Regards,
Steve

[Opium Motors]

Seeing that it is a fresh rebuild, important question, did you break in the cam? I.E. 2,500 RPM 20 minutes initial run time.

[bheston]

Great feedback! Thank you. 

- Running the stock exhaust manifolds. 
- The heat-riser valve replaced with a straight-through adapter.
- Standard volume/standard pressure oil pump because I'm running a stock 5qt oil pan.
- Engine was carefully broken-in by the engine builder himself running the car at 2000-2500RPM for 20-30 minutes using SAE 30 dinosaur break-in oil.

I watched the YouTube videos of the poor quality out-of-the-box fully assembled heads.  Seems like most issues are poor valve seats.  With the good leak down results, the valves seem to be sealing as expected for me.  I don't get any smoke on start-up, so I'm not sure the valve seal are an issue but reasonably easy to replace.  Of course, the guides could be an issue.  Good feedback on the oil accumulation.  I will take a peek at the drainage passages.     

[Kelley W King]

I think you have it narrowed down now. Some HP valve springs are thicker and have been known to pull up the umbrella type seals. Even if they look like they fit they will touch at full lift. Just a thought.

[Stingr69]

Intake manifold port gasket leak is very common on fresh builds.

[bheston]

Good point on intake gasket.  I will re-torque to be certain.