Hi, sharing something that has really been driving me nuts, 4-5 weeks, huge clouds of smoke on starting then calms down with driving , but same thing happens next time. Heads done, new valve seals, guides good. (not by me, prior owner ) .To make a very long painful dance very very short, the drains in the block are about a 5.5” long 5/16 hole . They were clogged solid the whole 5” with hardened crud; crud so hard we needed a drill to remove. On this particular motor , block drain hole is not aligned with head drain hole there is a sideways 5/16 hole in head about 1.5” long with an external Welch plug where drilled. We thought that “dogleg” was the obvious clog location , after figuring this out, (issue is NOT obvious) cleaned it and head, but still no go. Even 150 psi air with solvent soak did nothing, from head hole or at block deck. Drilled passage in head crosses over the locating dowel hole too, a too long dowel could stop it.
What it does, is valve cover fills with oil , apparently until it reaches exhaust guide top height, while running, then even more oil comes in until it finally runs down a push rod hole . Then after you stop engine it runs down exhaust stem, mostly into the back 2 cylinder , due to tilt, but I think pressure in exhaust valve stem space keeps it out till you stop motor , so runs ok. ; one symptom was oil wet , soaked heat riser valve, wet with the oil which had run inside exhaust manifold via exhaust valve and cylinder space while parked. And oil drips were on rear exhaust studs. (what?) First crank of engine pushes it out into manifolds, wets stuff. . Baffling thing at first---- easy to say “obvious “ now. Lots of theories at first, (“exhaust studs not sealed” (into water not oil) “cracks” (will go into water) , broken valve guide, loose valve guide; all wrong. In fact someone before me had pulled same head , put umbrella seals on exhaust valves , which are not supposed to be sealed .Sorry, that thinking was all wrong.
So bottom line, if working on an engine, manually clear these rear drain holes end to end with a long 5/16 drill. Possibly can get at them from pan, but easy if head off This engine was a poly head but block and drain is identical setup on hemi , possibly hemi drains are in line through head , I did not check, ---but that does not matter, as this must have stopped up at first in lower block. . Do not put paint in that space in head where valve springs are..we think paint peelings started / aggravated this , as well as lack of oil maintenance, crankcase venting, old oil technology back then . . That gooey tar like “junk” you find in an old pan is solid in these holes—and apparently hardens like black cement with engine heat. .
At least we know why…..now.
Same “coronary blockage” syndrome must apply to all 65 year old engine head oil drains ; I really do not think the hot tank would have got at this stuff--- 2.5” in …and really hard.
Posted by: "John Grady" <jkg@xxxxxxxxxxxxxxxxx>
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