Ford 460 low compression and rough idle
I just got a F350 with a 460 with 160,000 miles. I'm told by the PO that it has low compression in two cylinders (# 1 and #5). It's not drivable, but it starts. I let it idle for about 10 minutes and I saw lots of gray smoke from the tail pipe and none from the oil fill hole.
This makes me think that the piston rings are bad, but the heads are good, is this a correct assumption?
Second; the rough idle could be a stretched timing chain, correct???
Also, can the timing chain be the cause and cure for low compression?