340 smoking out left exhaust only

abodyfan said

It smokes the worst when idling. I know it’s cylinder 7 by looking at the plugs. When I drive and come back home it smokes a little if I let it idle after a few seconds it starts to spew smoke bad. One thing I forgot to mention is it pushing more than usual oil out of the breather on the valve cover. The breather is on the left side same as cylinder 7. It doesn’t have excessive amount of pressure in the crank case.

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Well, if it is pushing more than normal oil out of the breather, then it pretty obviously has more pressure in the crankcase. An intake seal gone would explain the the smoking, especially at idle, but not the pressure in the crankcase/under the valve cover.

The head gasket starting to fail seems to me to be the most likely explanation despite the compression numbers, and would make sense to let go when you got on it hard, and would explain both the smoking at idle and the extra oil out of the breather; IMHO, it is those 2 things together that point to the chamber seal failing, and not the intake seal. Otherwise, rings.

Have you done a leak down with 80 psi pressure in the cylinder? (Not the 15 psi that a Harbor Freight leakdown tester does....)