Fresh 235 rebuild. White grey smoke. Grey oil. Decided to pull the head to see if it had any damage/defect. Head gasket was in good condition, here is the but. #5 cylinder is black and #4 doesn't look like it has been fired at all. The 4 other cylinders look appropriate for the amount it has run. Head and block were planed by shop. My questions are: 1 why the grey oil? Coolant/ oil mix? From where? 2 what's up with #5 being black? 3 what's up with #4? Sounds electrical? Any other suggestions are welcome.
Sounds like water in the oil, all right. Check for head bolts not threading in far enough. Just screw them in with the head off and measure. Then recheck the gasket, head, and block surface very carefully.
You didn't run a compression check before taking it apart, did you? or check valve action/adjustment, look at the plugs, etc?
The plugs all looks pretty dirty with the exception of cylinder 4 which looked pretty clean. I did not run a pressure check. I figured I had diagnosed the problem with the color of the oil. Should have though. The only thing I can think of is a cracked head at #4 allowing coolant in. But that doesn't explain #5 being so black. Or does it?
Are you sure you have the firing order correct? Sounds dumb - but its a simple mistake we have all made at one point or another. Water mixed with oil usually results in a chocolately-brown color, not gray.
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