[cadillac_al]

Since these engines weren't meant for unleaded fuel, the heads and valves supposedly erode and don't last very long. I personally haven't driven any old engines that far for that to happen. It sounds like that's what may have happened to your engine though If that is the case it really should have at least one cylinder with low compression. I'm surprised the machine shop that worked on your heads didn't try to sell you on a good valve job with hardened valve seats to make it unleaded compatible. He missed a marketing opportunity there. The car would probably sell for a better price if it had a valve job with hardened seats. I think I would have a hard time pulling the heads off unless I definitely had a dead cylinder but it is just a matter of time anyway.