I have a 2007 trailblazer with a 4.2L. I was changing spark plugs and didn't notice until after I had cracked the porcilin on one plug and it had fallen into the cylinder. When i started the engine there was a bad knock and i shut it down when I saw what had happened to the spark plug I had it towed to the garage. they said damaged piston and probable hole in valve. recommended a used engine. Last time I changed a engine or tore one down It was a 350 and I had room to work. How bad is it to do on this truck or should i attempt to rebuild the current engine?

 

How many miles are on the engine? Does it run good? Does it need to be rebuilt anyway? Pull the head and see how bad the cylinder wall is damaged. If it is only the valve and the piston and the engine is in good shape otherwise, I would repair it.