1984 Oldsmobile Cutlass Supreme mileage: rebuilt. I re-gasketed a previously owned engine and put it in my car. I was traveling roughly at 65-70 mph when the car lacked all power and gave the car behind me a blue smoke bath. I pulled over at that time and checked the #4 spark plug and it was coated with oil. At that moment I thought my valve seals were shot. I towed the car home, opened the subject up, and found that along with valve seals the #1 exhaust valve had a pie slice hole in it. In addition, the #4 piston had a hole in the top of it. I am not a certified mechanic but I think though I may be wrong that the spark plugs that I was using were at the wrong heat range. I was using AC Delco's rapid-fire. If you would tell me why there was a hole in the piston and why there was a hole in the valve, I would be very grateful to your service.
The problems with the exhaust valve and the failed piston are probably due to that cylinder running lean. Check the injector for that cylinder and also look for vacuum leaks that would affect that cylinder. We do not think the wrong heat range of spark plugs would cause the problem you describe.