Greetings all from Canada.
I had the heads on my 312 done June 6 because of a bad misfire on #5. When the heads were done the machine shop stated that the valve were all in good shape. He put in hardened valve seats on the exhaust side, cleaned & rebuilt the valve train. The car ran great for about 4-5 weeks, very smooth, no carbon tracks out of the tail pipes and the exhaust smell was low. Last week I noticed black oil dripping out of the downdraft tube. I smelled a strong trace of fuel in the oil. I suspect it is wash down. I pulled the plugs, and found the 4 rear spark plugs vary a bit but are all clean dry and slight degrees of a tan colour. The front 4 plugs generally are a bit darker than the back, but #5 and #2 are very black, fouled & misfiring. There is a stronger smell of exhaust & some carbon tracking out of the tail pipes. There is no oil residue on any of the plugs. The car does not smoke. When the plugs are clean it runs very smooth without a hitch and has good power. It pulls about 18.5 inches of vacuum with a steady needle on the gauge. The valve lash was just recently checked and are spot on. I have tried swapping clean plugs from the back cylinders to #5 & #2 but they fouled within 5 minutes. I have put about 1000 miles on the car since the heads were done. All plugs, rotor cap & wires are all new. I am running Pertronix ignitor 1 and the MSD Blaster coil. One thing I noticed when the heads were off was how little carbon build up there was on the piston tops especially on #5. I hope I did not do any damage with the wash down.
Does this sound like piston rings are gone? Any ball park price on an engine rebuild?
Thanks all

Nat;
Have you done a compression test?
Rono

  Ron Lane,  Meridian, ID

Nat.  I’ll suggest performing both a cranking compression test and a leak down test on all the cylinders.  When doing the cranking compression test, do it with the throttle wide open and then you are looking for all the cylinders to be within 10% of each other in their readings.  If there is a low reading, then add oil to the low cylinder(s) and if the reading is higher on the recheck, then the rings are suspect.  A leak down test will be more definitive but it will also include head gasket and valve seating sealing so if you get a ‘high leakage’ reading with that test, then you’ll have to determine if the leakage is at a point other than the rings.

Lorena, Texas (South of Waco)

Just did a compression test on all 8 cylinders lowest was 149 lbs - highest 155 lbs all other 6 were 150 lbs.
They all held their pressure did not leak down.
We found the new coil wire carbon was NOT folded over the jacket and secured and crimped under the brass sleeve.
The carbon filament was standing straight up about 1/8" long and was arcing across the inside of the brass sleeve. It is all white.
I have trimmed back the jacket

If fuel fowling:

2 or 4 barrel?  With 4 barrel, the front 4 cylinders get most fuel from the primaries and the rear 4 cylinders get most from the secondaries.  Of course, if it is vacuum secondaries, this may not apply so much on the street.  I think #2 and #5 also draw fuel from the same plane, suggesting a greater problem with that particular barrel.

If 2 barrel or vacuum secondary 4 barrel, then maybe it is simply too rich and there is a vacuum leak common to the rear 4 cylinders (possibly the hole on the back, driver side is not plugged) causing it to lean out enough to look good yet not enough of a leak to cause a significant drop in vacuum.



Lawrenceville, GA

It is a holley 4160 (465 CFM)
we also found the front float a smidge high we lowered it.
keep you posted