big cam cummins

my air compressor is loud also, but builds air no worries so im not touching it unttil i have too. as for the rod having play that could cause a loud knocking noise like bigend bearing noise

 

Carbon buildup in the compressor lines can cause excessive noise, might be worth inspecting your lines and outlet 1st before you spend any $

 

Did anything happen unusual right before the knock started?

 

several ways to ck the cylinders, one easy way is with a crayon... Warm the engine up and mark on each exhaust port on the manifold, the coldest cylinder will melt the crayon the least. That will help narrow it down a lil bit. I've got lots of other tricks too if that helps.

 

sounds like fuel knock from a bad injector, once you have an idea of which head its comin from you can use the handle end of a hammer and push on rocker arms while engine is runnin to find the dead injector.

 

OK I would first check and see if the blow by is suddenly more than it was before the knock started, if you scored a liner it will knock and miss and also have a lot of blow by, the other thing is maybe pull the valve covers and make sure it didnt bend either a valve or injector pushrod. Also check all the crossheads on the valves. Does the jake brake still work ok? You can probably find the miss if you start it cold just keep feeling along the exhaust manifold while it warms up, the cylinder thats missing will still be cool while the cylinders firing will get warm. You might have lost the tip off an injector, that could explain the miss and the knock. If thats the case the oil might have fuel in it too. Take a long screwdriver or a broom handle and stick it up against your ear and use it to listen all around the engine where the knock is, you might be able to isolate it that way, kind of like a the way a doctor listens to you breathe through his steathascope.