So in the last offseason I pulled my motor out, and had the heads re-done essentially doing a top end rebuild. It seemed to run pretty good after I got the boat running again. Earlier this month I was running pretty close to wide open for a little bit across a bigger inland lake when the motor lost a lot of power. I backed off the throttle immediately and shut the motor down. I cranked the motor back over and it started right up. I noticed there was no oil pressure so I again shut it down. We towed it in and I check the oil pressure with a manual gauge. Again no pressure. We pulled the motor, and I pulled the heads. To my much disappointment there is a nice hole in number 4 piston. I haven’t had time to pull the pan yet. The cylinder to my surprise doesn’t look damaged at all. I am going to have that head checked to make sure the valves or seats were no damaged when the piston came apart. I understand the whole motor needs to get torn down, however my question is what caused number 4 to burn up? And is my oil pressure situation a coincidence, or is it related? I just want to make sure I have some background info as I get into this situation. When I did the top end rebuild I did have the distributor out, and a couple engine guys I have talked to said timing could have cause my issue. Any help from you Mark IV guys would be greatly appreciated. Thank You!

You detonated the motor to death, that's what burned the hole in the piston. Most of the time it'll get one of the center cylinders first, 3,5,4, or 6. You have no oil pressure because the detonation hammered the bearings all to hell and now the clearances are beyond excessive so the oil pushes right past, that equals no OP. Probably either high timing or not enough fuel is what got you.

Is this a carbureted engine?

This is the quadrajet carb'd motor. My future plans were to ditch the stock intake manifold and get a nice holley carb. Right now my main goal is to get the motor back up and running for now.

That motor came with the Q-jet so unless you have some serious carb issues that probably isn't the problem. The usual culprits are lean fuel mixture, high timing and to a lesser degree low octane fuel, extremely high ambient temps, excessive exhaust backpressure, or anything that could cause pre ignition. I did the same thing to an identical motor two years ago and never did get the cause nailed down. The motor right beside it was fine. Both were tuned the same. Happened on a hard pull that lasted about 3-4 minutes at the most. Once it starts it only takes a few seconds to destroy the engine.

If you think the hole in the piston is ugly wait until you take the rods off and unstrap the crankshaft.

I had a similar problem years ago, the motor backfired at season start up and blew one of the rubber plugs off the carb base plate ports. made it less than a mile at 3k rpm and blowtorched a perfect hole through #2 piston. took months to figure out what happened. Bob Madera made the right call based on the pics I posted. Insisted it was an air leak somewhere. I never looked at the carb until it was time to go to the dyno with the rebuilt motor. [ATTACH=CONFIG]526949[/ATTACH]

Loose and or wrong heat range plugs can go on the list. High water and or oil temp 2...

This is all great info and appreciate everyones input. I know there is a special procedure in setting the timing on these thunderbolt motors, and Im not sure if that was followed by the guy who helped me do it. I run the cross referenced autolite racing plugs. I was running 87 octane in the boat seeing that these things are lower compression. This may seem silly but the boat was very very low on fuel as well. I am now terrified to pull the pan off of this thing. Coming from a long backround of stock car racing I was hoping boating would be a little cheaper. Apparently I was wrong...... I am just hoping the internals including the block are saveable. With this being a bow tie block motor I really do not want to buy another block.

I'm sure your block will be fine. You won't like what you see when you get the bottom apart. There's a good chance the crankshaft will be cracked. Those GM forged cranks aren't the best pieces. Please post your findings when you get it all apart.