An odd knock

[gone huntin]

A few weeks ago I started hearing a slight knock in my engine. It ONLY does it when the engine is at operating temperature, not cold and it's not a bearing noise. It only does it between 2000 and 3000 rpm and it goes away when #1 plug is disconnected. This noise has the same sound as detonation, but it's rhytmatic with engine speed. I was thinking piston skirt, but someone mentioned a bad lobe/lifter. Any ideas or opinions? This engine has 221k on it and still runs very well and has a constant 30psi of oil pressure @ idle.

 

[Hogback Fabrication]

Have you checked the plugs, timing (and firing order), etc.?

It could be something in the valvetrain too but I would agree with the piston issue (of course all the other stuff is easier to check)

 

[gone huntin]

Yeah, I replaced the plugs Tuesday and didn't see any odd fouling or deposits on the old ones. The engine runs great, no missing or anything, just the slight knock after it warms up. Somedays I don't hear it until I've driven 8 miles to work. I had thought about carbon and I ran a can of Seafoam through it but it didn't change anything.

 

[NewUser]

sounds like a wristpin to me