Vintage Circa 1970 B20 smoke from valve cover oil cap

Seeking best suggestions for smoke coming from oil cap in valve cover. Engine starts and seems to run relatively fine - do need to sync and tune SU carbs. Just replaced older PCV system as the car is a 64 with transplant B20. Replaced PCV system as a result of last fall engine suddenly coming to semi-abrupt poor running condition. First I thought it was starved for fuel from clogged fuel filter. Then found there was oil pushing out from many places and a leak. Replaced about a quart over a month and attempted drives and fixes. Thought issue was clogged PCV system which looked good overall - hoses, etc. not clogged, but could not see in slim sandwich adaptor used between front carb and manifold, so thought this may be issue. Now thinking it may not have been clogged at all. Now think I may have caused carbon breakup using some modern semi-synthetic oil since last spring, which has caused a stuck piston ring or other. Last week, it started and ran for a 10 minute drive, but then smoke coming from oil cap filter. Reverted last fall back to natural 10w-30, still looks golden brown without sign of metal. Was told it may be gas getting into oil from flooding with out of tune carbs (choke open and pumping or holding to start when cold - ambient 50 F.). Or, if stuck piston ring may be able to drain some oil and add quart of Marvel Mystery OIl or a decarboniszer to loosen the piston ring. Have to do compression test, but still cold outside. Any insights greatly appreciated!!

Need to do compression & leakdown tests to determine your next course of action. Those two (not compression alone) will absolutely tell you if you have blowby causing the crankcase pressure.

Go here for a discussion of PCV arrangements for the B18 and B20.

https://www.sw-em.com/pcv_diagrams_and_notes.htm

Make sure that your PCV system is correctly set up. I have seen a lot of creativity applied to the B18 / 20 PCV systems which has not been good creativity. What is the sandwich adapter? Synthetic or semi synthetic oils are generally more immune to the formation of deposits that conventional oils.

If the PCV system is correctly set up, then do the compression test. If the compression numbers are bad the leakdown test can help diagnose where the problem is - or just get an adapter to pressurize the cylinder through the spark plug hole and listen for where the air is leaking from

Yeah, a considerable change in theory between the B18 (started off with an open dump tube) and the B20 (had a little orifice to actively pull fumes in at idle, then an open dump tube to the carb to anything other than idle).

But in general, unless you've got it hosed up really wrong (small pun?) like the only breather hose going to the fitting with the tiny orifice, then it should probably be able to handle a normal amount of blow-by. And if you have waaay too much blow-by, it's not really a crankcase ventilation problem.

Feel free to try to revive it with various snake-oils (Marvel oil, seafoam, atf in the gas, whatever people do) but I'd plan on a proper diagnosis to verify compression is leaking past the rings into the crankcase, and then plan on pulling it and taking it apart to see why that is happening.

everyhumanvovo said:

Have to do compression test

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JohnMc said:

a proper diagnosis to verify compression

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Absolutely.
I'm surprised how often this simple (cheap) test on old engines is ignored.

Admittedly, in my youth, I didn't do them either and would just throw parts .