Question from Joseph:
I had a problem with fouling plugs also, turns out the valve stem umbrellas (seals) were gone from years of heat they turn hard and crumble off the valves. The new seals cost about $25 for the good ones with wire reinforcing. A good Mopar mechanic can replace the seals by charging each cylinder with compressed air and releasing the valve spring keepers to expose the seals and replace them without removing the heads. Worked wonders on my car.
Reply from Frank:
When an engine sits idle for a while (not used at all) the valve seals almost always dry out and crack up. Engine oil then can run down the valve stems and burn in the combustion chamber. The piston rings can also seize in place, either: by rusting to the cylinder wall so that their sealing edges, when broken free by starting, don't seal anymore; or by the rings seizing in place in their piston grooves so that they don't expand outward to seal. When this happens to the lowest ring, the oil control ring, the engine will burn oil. Ring problems require a bottom end job.
Assuming that the compression is good you can replace the valve seals yourself. You don't have to take the car to a mechanic to do this job. I've done it, most recently on a '76 New Yorker. Get the best quality seals that you're auto parts guy has. (Shop around to get a quality name brand.) Tools required: Compression tester, cylinder leakage tester or spark plug adapter fitting (something that you can use to put compressed air into the cylinder); air compressor; torque wrench; valve spring compressor; common 3/8 ratchet set. You don't need a monster air compressor, the volume of air flow is quite low, but the pressure is pretty high.
I used my own valve spring compressor which was nothing more than a U shaped rod, bent to fit under a dowel bolted in place of the rocker arm. The U-rod hooked under the dowel and I could press down on the closed part of the U while removing the spring keepers. Worked better than the commercial tool, which I thought was a pain in the butt to use. (For a small guy, I have large fingers and this tool gave more room to work than the tool I bought. If I can find it again I'll scan a photo of it, and post the JPEG.)
1) Pull rocker arm covers. Remove old gasket material.
2) Remove rocker arm. Mark the front/back end of the arm and the locations of each bolt.
3) Remove and mark each push rod. They must go back into their original positions. Mark also Top & Bottom
4) Remove spark plugs
5) Thread the fitting into a plug hole, connect the air line and pressurize to about 100 PSI
6) Using the spring compressor press down on the washer above the spring. You may need to use a small screw driver to remove the keeper from the top of the valve stem. (The keeper looks like a cone cut in half along its longitudinal axis.)
7) Remove the spring assembly.
8) Remove the old seal. It may be broken, remove all the pieces you can.
9) Install the new seal. The intake and exhaust valve seals are different!
10) Replace spring assembly
11) Compress spring with tool and re-install keeper.
12) Repeat 6-11 for the other valve on the cylinder
13) Release air pressure from the cylinder and remove air fitting
14) Repeat 5-13 for each of the other 7 cylinders
15) Reinstall push rods - observe original positions
16) Reinstall rocker arm - observe original positions
17) Reinstall valve covers with new gaskets. Don't use sealer since it can break off and migrate through the engine. Tighten carefully to just snug down the cover against the gasket. Over-tightening ensures leaks!
18) Reinstall plugs. (Since they're out and cheap, might as well put in new ones.)
If you are a belt-and-suspenders kind of guy, you can turn the engine so that the piston of the cylinder you are working on is at TDC, preventing the valve from falling into the engine. I don't think that this is necessary since these engines have BIG valves, about 2" in diameter, which at 100 PSI of pressure means that there is about 300 pounds of force holding the valve closed. If you need to put anywhere near that much force into doing this, you're doing something wrong. [ Closing force (pounds) = Pi * r ^ 2 * PSI ]
First time I did this it took probably about 3-4 hours. Now about half of that.
Excellent advice on replacing valve seals. I've found having a magnetic stick at my side was a great help....those pesky "keeper cones" that are split in half have a habit of going off in the wrong direction. I use the magnet to take out the halves once they are loose and placing them back in place at jobs end.