Got a customer that had a 3304 CAT engine, in a rubber tired loader, that had a slight top end knock. After changing injector nozzles, getting the fuel supply lines unblocked (new filters, cleaning nearly plugged line out of the tank, etc), putting in an air filter that wasn't clogged up nearly level full on the pleats, and removing the loose parts shaking around inside what was left of the muffler, I had 99.9999999% of the knock out of it. The remaing knock I simply attributed to a normal diesel knock, as that sounded like what it was.
Got done working on the machine and got in to move it. Put it in gear, reved it up to back it out of it's parking spot, and the engine decided to rev even more on it's own. All I heard was RRRRRRRRRRR...BLAM. When I saw oil all over the tire I knew there was a problem.
Went inside and told the customer I had good news and bad news, which did he want first? He said the good, so I told him I had all of the knock out of the engine. He than asked what the 'bad' was.....So, I told him that it had taken a hole in the side of the block about 'yea' big to finally get the last of it out.
Thankfully he knew the machine was on it's last leg anyway so he wasn't really that upset, and simply told me to go ahead and transfer all the new parts to the other machine so it woul maybe run a little longer.