68 Z/28 Engine Smoking - Any Ideas?

[Lynn]

If you have already torn into the engine then disregard this. However, I would approach it this way.

First, I doubt it is valve seals based on this statement: “What it is doing is smoking occasionally, sometimes really badly. This seems to happen only at idle speeds.” Normally, an engine with bad valve seals will smoke on initial startup when cold.

Because it only seems to smoke at idle, I would suspect the carb is “loading up” a bit. Depending on how high the idle speed is set, it might not actually stumble before smoking. Could be a power valve, needle and seat, float. Eric can help you diagnose the carb. There is no one better with a Holley.


If you want to eliminate rings, valve guides and valve seals without tearing into it, take it for a spin, get it up to operation temp, lightly accelerate in second gear up to 5000 RPM, and let off the gas, but don’t hit the brake at all. Let the engine brake. If it has poor ring seal, bad valve seals etc. (or even a leak at the intake underneath so that it can draw in oil into an intake port, as someone has suggested) then it will billow gray smoke, guaranteed. If it doesn’t, you know it is not internal to the engine, and save a lot of tear down time chasing rabbits that aren’t there.

Hope this helps.