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« on: April 16, 2020, 01:15:43 AM »
I had something similar in my 67 F250 with 390 & NP435. Taking off, wouldnt smoke, shifted below 2500-3000 it wouldnt smoke either, but higher and it would. Thought maybe too much oil up top sucking it out the pvc, so I restricted the oil coming up top. That wasnt it. Thought valve guide seals, they were a bit hard, but still pliable and all 16 were whole, still replaced with alex's parts positive seal (the ones for factory sized guides). Same problem. Just kept driving the truck as it was my only means, so I would just short shift. Then it started to get worse, it would start to smoke on shifts no matter the RPM, but it was erratic. Then once in a while, it would throw a bunch of smoke out of the exhaust when I would take off from a stop, I could tell it was going to do it as it would just slightly start to run rough right before it did it. It was embarrassing to me as it would leave this huge smoke ball that would just linger. Finally took the valve covers off and it was the intake gasket. The #3 & #6 intake gasket separated near the top. Weirdest thing I ever saw. Fixed it, still smoked a bit, but after a couple months, no smoke. Like they said before, some residual oil I figure in the exhaust. In the one picture, you can see the #6 gasket sticking up slightly.
This truck has C6AE-U heads and CJ intake.
Keith