I've been living with a smoking 390 for a while, but have begun to dig into it more after new developments. I purchased my 66 Galaxie back in 2014 with a smoke issue; I got a good deal on it because of the issue. I got it home and did some research. I put restrictors in the oil passage for the rockers (64 jet), replaced the umbrella seals on the intake valves (my dumbass didn't do the exhaust), and replaced the intake gaskets using ultra black sealant on the gaskets and in place of the end corks. It cleared up most of the smoke for quite a while, but it began to develop again. The plugs always looked good, but recently I pulled plugs after noticing it pretty much constantly smokes out the passenger bank--#3 was oil fouled. I replaced the plug and drove it no more than 10 miles, brought it home and rechecked the plug, it was already oil soaked. Leakdown on the cylinder was about 17-18% and leaking out valve cover filler cap. I didn't do a compression check.
I pulled the intake tonight thinkinking it is sucking oil, but I don't see any clear evidence. Could worn valve guides cause a plug to foul this quickly? Could it be a broken ring with that leakdown result? It didn't seem an excessive leakdown, given what I've read.
I'm not certain how to proceed. Thoughts and opinions please....