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I did a rebuild on the 77 900ss, but got a tank full of what seemed to be a mix of gas and deisel (500 miles into the run in), needless to say the rings didnt seat. I have rebuilt the top end(honed new rings), but I still have a smokey front cylnder, the plug isnt fowling, the cylnder looks clean, and it doesnt smoke straight away. It takes about a minute befor it starts, and then it smokes for a while then stops.

My guess is oil is leaking into the exhaust, and doesnt cause smoke till its hot, which would mean the exhaust valve O ring?.

Anybody like to second guess my guess?

My guess is valve stem seals or guide wear. On a vertical cylinder this will normally show on start up, as the oil can leak down the valve stem after the engine is stopped. In this case, a horizontal cylinder, if it blows smoke after idling or running around 2000 rpm for a while the intake manifold suction could be sucking the oil through the inlet valve stem and seal assembly.

Thanks Colin, guess I'll be taking the head of yet again.